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Exploring alternative futures of the World Water System.
Building a second generation of World Water Scenarios
Driving force: Water Resources and Ecosystems
Martina Bertsch 2010
Prepared for the United Nations World Water Assessment Programme UN WWAP
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Table of contents 1. Introduction2. Current assessment of the driver 2.1. Ecosystem services 2.2. Water resources 2.3. Floods and droughts 2.4. Biodiversity and invasive species 2.5. Deforestation 2.6. Water availability, use and productivity 2.7. Water quality 3. Possible future developments in the domain of the driver 3.1. Ecosystem services 3.2. Water resources 3.3. Floods and droughts 3.4. Biodiversity and invasive species 3.5. Deforestation 3.6. Water availability, use and productivity 3.7. Water quality Acknowledgements Bibliography
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1. Introduction This report examines global ecosystems as a driving force impacting the water resources.
The report begins with a description of the current state of global ecosystems and water resources, depicted through a series of key elements and their complex interactions and interdependencies. It identifies major impacts on the current state. It then extracts major trends and projections for future states from available global scenarios. The table of possible developments is provided, detailing events, time factors, positive and negative impacts on water resources, low probability developments and principal sources of information. Causal links are established between this driver and the other nine water drivers. Lastly, critical uncertainties and future research needs are identified. Driver elements analyzed in this report include: 1) Value of ecosystem services; 2) Freshwater resources (e.g., wetlands); 3) Extreme climate/water‐related events (floods and droughts); 4) Biodiversity and invasive alien species; 5) Changes in land use (deforestation); 6) Changes in water availability, use and productivity, including groundwater overdraft; 7) Changes in water quality (e.g., eutrophication).
2. Current assessment of the driver
2.1. ECOSYSTEM SERVICES An ecosystem is a dynamic complex of plant, animal and microorganism communities and
the nonliving environment interacting as a functional unit. Humans are an integral part of ecosystems. The Millennium Ecosystem Assessment (MA, 2005) defines ecosystem services as benefits provided to people, comprising: 1) Provisioning services, i.e., the products obtained from ecosystems, including fresh water, food, fuel, fiber, biochemical and genetic resources. 2) Regulating services, i.e., the benefits obtained from the regulation of ecosystem processes, including climate regulation, air quality maintenance, regulation of hydrological flows, water purification, human disease and pest control, pollination, coastal protection, flood and erosion control. 3) Cultural services, i.e., the nonmaterial benefits obtained from ecosystems through spiritual enrichment, cognitive development, reflection, recreation and aesthetic experiences. 4) Supporting services, necessary for the production of other services, e.g., oxygen production, soil formation, nutrient storage, recycling, processing and acquisition.1
1 Provision and regulation of water by aquatic ecosystems is essential for numerous biochemical and
geochemical processes. Another important service attributed to aquatic ecosystems is provisioning of fish and seafood. Fish are an important source of proteins, micronutrients, minerals and essential fatty acids, and significantly contribute to the diets of many communities. Globally, 1 billion people rely on fish as their main source of animal proteins, and some small island nations depend on fish almost exclusively. According to FAO (1999), 79% of fish products are harvested from marine sources.
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The ability of any particular aquatic ecosystem to supply the range of services listed above depends upon a variety of factors, e.g., the type of ecosystem, the presence of key species, management interventions, the location of human communities, the surrounding climate and topography. Few sites have the capacity to provide all of the above services. Generally, the more biologically diverse an ecosystem is, the greater the range of services that can be derived from it (MA, 2005).
Current decision‐making processes often ignore or underestimate the value of ecosystem services. There are two paradigms of value:
1) The anthropocentric (utilitarian) concept is based on the principle of humans’ preference satisfaction (welfare). Ecosystem services have value to societies because people directly or indirectly derive utility from their use (use values). Value is often ascribed to knowing that a resource exists even if people never use that resource directly (non‐use or existence values), e.g., the deeply held historical, national, ethical, religious and spiritual values ascribed to ecosystems.
2) The non‐utilitarian paradigm holds that an ecosystem can have intrinsic value irrespective of its contribution to human well‐being. Intrinsic value may complement or counterbalance considerations of utilitarian value (Alcamo et al., 2005).
Well‐documented impacts of human activities on ecosystem services at a variety of scales include changes in the number and distribution of species (Chapin et al., 2000; Higgins et al., 2002; Sala et al., 2000), and the quality and quantity of fresh water (Brinson and Malvarez, 2002).
For certain ecosystem services, monetary values are estimated.2 Conversely, ecological
degradation results in economic losses. Coastal erosion from altered currents and sediment loads can be caused by changes in coastal and upstream land use. The beaches largely disappear in areas where new ports are built, resulting in substantial tourism income losses. Societal consequences of altered biodiversity are also measured.3
MA (2005) reports that the degradation of lakes, rivers, marshes and groundwater systems
is more rapid than that of other ecosystems. The status of freshwater species is deteriorating faster than those of other ecosystems. Direct drivers of degradation of freshwater ecosystem services include: infrastructure development, land conversion, water withdrawal, eutrophication, pollution, overexploitation and the introduction of exotic species (Mayers et al., 2009). UNEP (2009a) provides a review of water security and ecosystem services case studies and lessons learned about habitat rehabilitation, pollution control and integrated watershed management.
2 Direct use values of water buffering (e.g., flood prevention) are estimated at US $350 billion at 1994 prices, and recreational values at US $304 billion (Costanza et al., 1997). It is estimated that reef habitats provide human beings with living resources (e.g., fish), and services (e.g., tourism returns and coastal protection), worth about US $375 billion each year (Costanza et al., 1997). 3 In the U.S., total annual damage associated with aquatic invasive species is estimated at $73 billion (the Nature Conservancy, 2010). Marginal water losses to the invasive star thistle in the Sacramento River valley, U.S., are valued at US $16-56 million per year. In South Africa's Cape region, the presence of rapidly transpiring exotic pines raises the unit cost of water procurement by nearly 30%. Increased evapotranspiration due to the invasion of Tamarix in the U.S. costs an estimated US $65-180 million per year in reduced municipal and agricultural water supplies. The presence of sediment-trapping Tamarix also narrows river channels and obstructed over-bank flows, increasing annual flood damages by $50 million (as cited by Chapin et al., 2000).
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2.2. WATER RESOURCES
Less than 3% of the global total water resources is represented by freshwater and less than 1% of that (less than 0.01% of total water) occurs in the Earth’s liquid surface freshwater. The remainder represents ice‐caps or groundwater. The small fraction of liquid surface freshwater hosts an extraordinary level of biodiversity supported through a range of freshwater ecosystem types: 1) running waters, 2) standing waters and 3) areas of transient water availability. Freshwater ecosystems include: permanent and temporary rivers and streams; permanent lakes, reservoirs; seasonal lakes, marshes and swamps, including floodplains; forested, alpine and tundra wetlands; springs and oases; groundwater systems and geothermal wetlands (Mayers et al., 2009).
The volume of water in rivers and streams is only a fraction of the water in the entire hydrosphere, but often this water constitutes the most accessible and important water resource (WWDR3, 2003). Uneven global distribution of precipitation and runoff influence the distribution of river networks. Asia and Latin America each contribute approximately 30% of the world freshwater discharged into the ocean, North America contributes 17, Africa 10, Europe 7, and Australasia 2% (Fekete et al., 1999). There are several published inventories of rivers, listing the major river systems with their drainage area, length and average runoff (e.g., Shiklomanov, 1997). The variability between estimates can be explained by different definitions regarding the extent of a river system and different time periods or locations for the measurement.
There are 5‐15 million lakes across the globe (WWDR3, 2003) and approximately 10,000
lakes have a surface area over 1 km2. Only about 15‐20 existing lakes in the world are older than 1 million years (LakeNet, 2003). A disproportional share of large lakes, with a surface area over 500 km2, is found in North America, where glacial scouring created many depressions in which lakes have formed. The International Lake Environment Committee (ILEC) maintains a database of over 500 lakes worldwide, with some physiographic, biological and socioeconomic information.
The definition of inland wetlands adopted by the Convention on Wetlands (Ramsar, Iran,
1971) covers all wetland types, including artificial wetlands, and encompasses permanent and temporary riverine, lacustrine and palustrine systems, above ground and underground systems (karst and cave), freshwater, brackish and saline systems (Ramsar Classification System for Wetland Type in the Annex to Resolution VII.11). A Global Review of Wetland Resources and Priorities for Wetland Inventory (GRoWI, Finlayson & Spiers, 1999) estimated the global extent of wetlands including coastal wetlands in some countries, at 1,276‐1,279 million hectares (ha).4 Revenga and Kura (2003) offer some reasons for the incompleteness of global wetland inventories, notably inconsistent interpretations of definitions, difficulty defining the boundaries, limitation of maps and remote sensing products.
4 Compared with previous estimates of inland waters of 530-970 million ha. These estimates include 530 million ha for natural freshwater wetlands. A substantial portion of the inland water resource is known to be peatland. The Global Peatland Initiative estimates coverage of 324 million ha, or 25-46% of the total area of inland waters from different sources. Cultivated rice paddies also form a significant area of the inland resource, covering at least 130 million ha (Aselmann and Crutzen, 1989).
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During the past hundred years, the groundwater portion of the water cycle was subjected to massive changes, as humans learned to dig or drill wells and abstract groundwater using pumps. Groundwater serves as a water shortage buffer during short‐term climate variations and is important to adaptation strategies. Groundwater mining from fossil aquifers is often the only reliable means of obtaining water.
These groundwater resources are increasingly being used for agricultural, industrial and
domestic water supplies, although they are almost never recharged. Changing land use and water infrastructure also greatly modify groundwater regimes, with groundwater pumping from deep aquifers now a worldwide phenomenon. In many instances, groundwater is pumped with no understanding of its source or its annual recharge, and therefore of how much may be used sustainably. Heavy groundwater pumping has led to unsustainable conditions. Stresses result in: 1) Falling water levels; 2) Degraded groundwater aquifers; 3) Increased salinization; 4) Chemical and microbiological pollution; 5) Desiccated wetlands; 6) Dewatered rock sequences; 7) Land subsidence. Use of groundwater for irrigated agriculture increased enormously in the past 50 years. Some 70% of global groundwater abstraction is now estimated to be used in irrigation. Pollution of shallow aquifers became widespread four or five decades ago and triggered water quality protection measures in many countries. Groundwater abstractions also contributed to the development of rural economies.
2.3. FLOODS AND DROUGHTS
Extreme climate/water‐related events can have positive and negative impacts on ecosystems and their services. They recharge natural ecosystems, providing more abundant water for food production, health and sanitation. But extreme water‐related events also destroy lives and property. Adikari and Yoshitani (2009) analyze water‐related disaster events between 1980 and 2006.5 The factors that lead to increased water‐related disasters include: natural pressures, e.g., climate variability; management pressures, e.g., lack of appropriate organizational systems and inappropriate land management; and social pressures, e.g., escalation of population and settlements in high‐risk areas (particularly for poor people).
Flooding is broadly defined to include both excess water caused by rainstorms that subsequently leads rivers to flood (spill over their banks), and severe coastal storms or cyclones that can lead to excess water through largely tidal surges (Cosgrove and Rijsberman, 2000). The moisture‐holding capacity of the atmosphere has been increasing at a rate of about 7% per 1°C of warming, creating the potential for heavier precipitation. There have likely been increases in the number of heavy precipitation events in many land regions, consistent with a warming climate and
5 Numbers of floods and windstorms increase drastically from 1997 to 2006 (factor of 2 and 1.5, respectively), but other types of disasters do not increase significantly in this period. Drought is severe at the beginning of the 1980’s and gains momentum again during the late 1990’s and afterwards. The numbers of landslides and waterborne epidemics are highest during 1998–2000 and then decrease. Waves and surges increase between 1980 and 2006. In general, water-related disaster fatalities follow a decreasing trend, but the fatalities record has occasional peaks: droughts, during the period 1983–1985; windstorms, 1989–1991; waves and surges, 2004–2006. Global estimates of water-related economic losses show an increasing trend, the main contributors in descending order being windstorms, floods and droughts; the rest of the water-related disasters are insignificant, but underestimated (Adikari and Yoshitani, 2009).
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the observed increase in atmospheric water vapor, even where total precipitation has declined. Some people rely on floods for irrigation and natural fertilization, but disruption, devastation of human lives and infrastructure are common. Among the regions devastated by floods in the period 2001‐2010 were Southern China, Haiti, India, Indonesia, U.S., Mexico, South Eastern Europe and most recently Portugal. In developing countries extreme floods can result in many deaths, while in developed countries extreme floods cause material damage in the billions and tens of billions of dollars.
Van Lanen et al. (2007) define drought as a sustained and regionally extensive occurrence of below average natural water availability. The main causes are low precipitation and high evaporation rates. In regions with a cold climate, temperatures below zero can also give rise to a winter drought. Drought is characterized as a deviation from normal climate and hydrology, which is reflected in precipitation, soil water, groundwater and streamflow. Droughts have a substantial impact on the ecosystem and agriculture of the affected region. Climate change is expected to influence precipitation, temperature and potential evapotranspiration and to influence occurrence and severity of droughts. But it is difficult to disentangle the impacts of climate change from those of other human influences, e.g., engineered effects, land use changes and multidecadal climate variability. More intense droughts, affecting more people and linked to higher temperatures and decreased precipitation have been observed in the 21st century (Zhang et al., 2007). Burke et al. (2006) assess meteorological drought in the Hadley Centre global climate model using the Palmer Drought Severity Index (PDSI). On average, the limiting PDSI values for extreme, severe and moderate drought are −4.3, −3.3, and −2.0, respectively. The land surface in drought increased by the beginning of the 21st century for all three types of drought, from 1% to 3% for the extreme droughts, from 5% to 10% for the severe droughts, and from 20% to 28% for the moderate droughts.
2.4. BIODIVERSITY AND INVASIVE SPECIES Biodiversity is the variability among living organisms from all sources, including terrestrial,
marine and freshwater ecosystems. It is a composite measure of the number of species, i.e., species richness, and the number of individuals of different species, i.e., relative abundance (MA, 2005). It includes diversity within and between species and diversity of ecosystems. Freshwater biodiversity is high relative to the limited portion of the Earth’s surface covered by freshwater. Freshwater fish make up 40% of all fish, and freshwater molluscs make up 25% of all molluscs. Freshwater biodiversity tends to be greatest in tropical regions, with a large number of species in northern South America, central Africa, and Southeast Asia. Worldwide, the number of freshwater species is estimated to be between 9,000 and 25,000 (Cosgrove and Rijsberman, 2000). Revenga and Kura (2003) review inland water species richness, distribution and conservation status. Ecological indicators are catalogued by Olli and Tamminen (2006): inherently univariate indices; complex indices; marine benthic indices; entropy indices; river indices; and physiological indices.6
6 1) Inherently univariate indicators are simple to measure and interpret, e.g., sea surface temperature, secchi depth, concentration and percentage of dissolved oxygen, biological and chemical oxygen demand, bulk measurements of dissolved and particulate nutrients. They are included in routine monitoring programs and long time series are available; 2) Complex indices are various arithmetic combinations of univariate parameters; 3) Marine benthic indices rely on the paradigm stating that benthic communities respond to improvements in habitat quality in three steps: the abundance
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Changes in ecosystem biodiversity can influence the services they provide. In addition, the diversity of living species has intrinsic value independent of any human concern (Alcamo et al., 2005). A growing number of species and habitats are disappearing. According to the 2004 IUCN Red List of Threatened Species, a total of 15,589 species of plants and animals are threatened, facing a high risk of extinction in the near future, in almost all cases as a result of human activities. Since the beginning of the century, 50% of wetlands have disappeared. The loss of freshwater biodiversity is poorly monitored except for some larger, commercial species.7 The most important causes of biodiversity loss in freshwater systems are: 1) Habitat loss and degradation; 2) Water quality, not discussed in detail because of the lack of comprehensive data at global scale (Revenga and Kura, 2003); 3) Intentional and unintentional introduction of exotic or invasive alien species, IAS (Hill et al., 1997).
In some lake ecosystems, IAS are considered by some to be the primary cause of biodiversity loss (Ciruna et al., 2004). IAS can become established in an ecosystem as a result of political, demographic, cultural, socio‐economic or ecological factors. The rich endemic ichthyofauna of Lake Victoria in Africa have been reduced by predatory Nile perch, overfishing and eutrophication (McAllister et al., 1997). Today’s global spread of IAS is mainly driven by aquaculture, shipping and global commerce (Welcomme, 1988). Intentional introductions comprise exotic flora and fauna in gardens or waterways, or government‐sanctioned releases of organisms for propagation or harvest. Unintentional introductions occur as a result of the escape of aquaculture operations or the accidental transport of organisms attached to boats, structures, garbage or in ballast water. There is some correlation between levels of human activity, trade, ecological integrity and the resistance of ecosystems to invasion from introduced species (Ciruna et al., 2004). Degradation of ecosystem functions generally results in a greater susceptibility to invasions. In modern environmental management, a two‐phase solution is recommended to address aquatic IAS: 1) Prevention of their spread through education, partnership and policy; 2) Management of invasions and restoration of freshwater habitats.
IAS affect native species through predation, competition, disruption of food webs, alteration of water quality and the introduction of diseases. The species introduced include a
increases; species diversity increases; and dominant species change from pollution-tolerant to pollution-sensitive species; 4) Entropy indices are based on information theory; 5) River indices are incorporated into governmental monitoring programs and specific to one region or country. Many use specific indicator species, applicable to a restricted region or context. An important concept is the integration time of the environmental signal by the organisms. Unicellular phytoplankton or benthic diatoms respond rapidly to fluctuations in the environment, while sessile benthic fauna integrates over several years; 6) Physiological indices are usually expressed as ratios of physiological rates, e.g., the ratio of primary production to community respiration indicates the degree of heterotrophy of the system. Some physiological indices are very specialized and often use modern molecular techniques, e.g., evaluation of the total antioxidant status in algal tissue extracts to assess the stress response of algae to environmental impacts in urban aquatic habitats. 7 Over 37% of wetland dependant mammals, nearly one third of amphibian species and 50% of turtles are threatened with extinction; 41% of waterbird populations are in decline. Data suggest that 20–35% of freshwater fish are vulnerable or endangered, mostly because of habitat alteration. Other factors include pollution, non-native species and overharvesting.
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variety of taxa from fish (e.g., Asian carp8), higher plants (e.g., water hyacinth9) to invertebrates and microscopic plants (e.g., dinoflagellates10). Worldwide, two thirds of the freshwater species introduced into the tropics and more than 50% of those introduced to temperate regions become established (Welcomme, 1988). In aquaculture, exotic fish are usually introduced to enhance food production and recreational fisheries, or to control pests, e.g., mosquitoes and aquatic weeds. Introduced fish account for 96.2% of fish production in South America and 84.7% in Oceania (Garibaldi and Bartley, 1998). In Europe, North America, Australia and New Zealand, in 77% of cases native fish populations are reduced or eliminated following the introduction of exotic fish.
2.5. DEFORESTATION
Deforestation is the clearance of naturally occurring forests by logging and burning.11 Disregard or ignorance of intrinsic value, lack of ascribed value, lax forest management and deficient environmental law are some of the factors that allow deforestation to occur on a large scale. In many countries, deforestation is an ongoing issue that is causing extinction, changes to climatic conditions, desertification and displacement of indigenous people (FAO, 2005). Deforestation also significantly impacts the water cycle:
1) It reduces the content of water in the soil, groundwater and atmospheric moisture. Trees extract groundwater through their roots and release it into the atmosphere. When part of a forest is removed, the trees no longer evaporate away this water, resulting in a much drier climate.
2) It reduces soil cohesion, which results in erosion, flooding and landslides. Vegetation litter, stems and trunks slow down runoff. Roots create macropores in the soil that increase infiltration of water. 8 Asian carp have been found in the Illinois River, which connects the Mississippi River to Lake Michigan (USA). Two species of Asian carp (the bighead and silver carp) were imported by catfish farmers in the 1970’s to remove algae and suspended matter out of their ponds. During large floods in the early 1990’s, catfish farm ponds overflowed their banks, and the Asian carp were released into local waterways in the Mississippi River basin. They can weigh up to 100 pounds, and can grow to a length of more than four feet. They are well-suited to the climate of the Great Lakes region, which is similar to their native Asian habitats. Due to their large size and rapid rate of reproduction, these fish can disrupt the food chain that supports the native fish and pose a significant risk to the Great Lakes Ecosystem. Additionally, silver carp can leap several feet out of the water when disturbed by boat propellers, possibly causing damage to boats and injuries to boat operators and fishermen. To prevent the carp from entering the Great Lakes, USEPA and other authorities are working to install and maintain a permanent electric barrier between the fish and Lake Michigan (USEPA, 2004a). 9 Water hyacinth (Eichhornia crassipes) became invasive in many tropical and sub-tropical inland waters. Indigenous to the upper Amazon basin, it was spread throughout much of the planet for use as an ornamental plant beginning in the mid-19th century. By 1900, it spread to every continent except Europe. Today, the plant has a pan-tropical distribution. It quickly extends its range throughout rivers and lakes in the tropics, clogging waterways and infrastructure, reducing light and oxygen in freshwater systems, and causing changes in water chemistry and species assemblages (Hill et al., 1997). 10 Dinoflagellates are protists, mostly marine plankton, which sometimes bloom in concentrations of more than a million cells per milliliter. Certain species produce neurotoxins (e.g., saxitoxin, a powerful paralytic), which kill fish and accumulate in filter feeders, e.g., shellfish, which in turn cause poisoning in people. Their rapid and copious reproduction due to the abundant nutrients in the water can result in the red tide phenomenon. 11 Trees or derived charcoal are used or sold for fuel or as a commodity. Cleared land is used as pasture for livestock, plantations of commodities and settlements. The removal of trees without sufficient reforestation results in damage to habitat, biodiversity loss and aridity. Deforestation has adverse impacts on biosequestration of atmospheric carbon dioxide.
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3) It lessens the landscape’s capacity to intercept, retain and transpire precipitation. Instead of trapping precipitation, which then percolates to groundwater systems, deforested areas become sources of surface water runoff, which moves much faster than subsurface flows. That quicker transport of surface water can translate into flash flooding and more localized floods than would occur with the forest cover.
4) It contributes to decreased evapotranspiration, which lessens atmospheric moisture which can affect precipitation levels downwind from the deforested area, as water is not recycled to downwind forests, but is lost in runoff and returns directly to the oceans.
According to the FAO Global Forest Resource Assessment (FRA 2005), forests cover 30% of the total land area. The total forest area in 2005 is just under 4 billion ha, corresponding to an average of 0.62 ha per capita. But the area of forest is unevenly distributed: 64 countries with a combined population of 2 billion have less than 0.1 ha of forest per capita. The ten most forest‐rich countries account for two‐thirds of the total forest area. Seven countries or territories have no forest at all, and an additional 57 have forest on less than 10% of their total land area.
2.6. WATER AVAILABILITY, USE AND PRODUCTIVITY Water availability is critical for the maintenance of flora, fauna, freshwater systems and
human activities. Water is needed for forests and wetlands, which in turn recharge aquifers, store runoff and regulate pollution by processing organic waste (Johnson et al., 2001). Sufficient in‐stream water availability can help temper water pollution through the dilution of contaminants in the watercourse. Extreme changes in ecosystems may occur if water available for environmental uses falls below a certain threshold. There is a growing interest in understanding environmental demands for water. Environmental flows refer to the quality, quantity and timing of water flows required to protect an ecosystem, enable ecologically sustainable development and water resource utilization. The Nature Conservancy developed the following tools for environmental flow management: 1) Ecological Limits of Hydrologic Alteration12 (ELOHA); 2) Ecologically Sustainable Water Management13 (ESWM); and 3) Indicators of Hydrologic Alteration14 (IHA). The possible trade off between water for nature and water for food production can be a contentious issue, as demonstrated during the 2nd World Water Forum in The Hague (2000). Participants in the “Water for Food” theme stressed the need for slow growth in water consumption in agriculture, while the “Water for Nature” theme called for significant reallocation of water from agriculture to environmental uses.
12 ELOHA is a scientifically robust and flexible framework for assessing environmental flow needs across large regions (states, provinces, major river basins or entire countries), aimed at understanding the ecological ramifications of human-induced alterations in river flows. Information gathered through ELOHA allows water managers and stakeholders to develop environmental flow targets for rivers without requiring detailed, site-specific hydrologic or biological information for each river. 13 ESWM is a six step framework that determines how to meet human water needs by storing, diverting and releasing water in a manner that either sustains or restores a river’s ecological integrity. 14 IHA is a free software program developed by Nature Conservancy, which provides information for developing environmental flow recommendations and understanding the impacts of human activities on water flows. IHA displays statistical information about water flow changes and trends in multiple formats, e.g., comparing the flow in a particular river between pre-dam and post-dam periods.
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The total rainfall on the Earth’s land surfaces amounts to 110,000 cubic kilometers (km3). Rain replenishes blue water sources, i.e., rivers, lakes, etc, and green water, i.e., soil moisture. About 39% of rain contributes to blue water, supporting biodiversity, fisheries and aquatic ecosystems; 56% of green water is evapotranspired by landscape uses that support bioenergy, forest products, livestock grazing lands and biodiversity; 4.5% is evapotranspired by rainfed agriculture supporting crops and livestock; total evapotranspiration by irrigated agriculture is 2% of rain, of which 30% is directly from rain (green water) and the remainder from irrigation (blue water). Blue water withdrawals for irrigation, industry and municipal use represent 9% of total blue water. Cities and industries return more than 90% of their withdrawals to blue water, but the return flows are often of lower quality (Molden, 2007). Only a small fraction of the total available water is accessible by humans. Therefore, it is more useful to consider total water withdrawn for human use. Groundwater/Surface‐Water Maximum Allowable Water Withdrawals (G/S MAWW) are actual water withdrawals, which are constrained by allowable water withdrawal for surface water and groundwater. MAWW are limited by infrastructure constraints, e.g., physical diversion structures and pumping capacities, and policy constraints, e.g., the amount of water which must be left in‐stream for environmental purposes. Of the total water withdrawn for human uses, withdrawals for agriculture represent 70%, those for industry 20%, and for municipal use about 10%. Shiklomanov (1999) presents tables of the dynamics of water use by continents and by economic sectors. Between 1950 and 1995, agricultural uses for water more than doubled (Cosgrove and Rijsberman, 2000; Shiklomanov, 1999). Sixty years ago, the world population was smaller, less wealthy, consumed fewer calories, ate less meat and required less water to produce their food. When agricultural activities change the quality, quantity and timing of water flows to support food provision, the ecosystems’ capacity to provide other services is reduced. Regulating services are primarily affected: pollination, biological pest control, flood retention capacity, changes in microclimate regulation, the loss of biodiversity and habitats (Molden, 2007). The development of dams and irrigation systems has significant environmental and human resettlement costs, e.g., 48 million people were displaced by dam projects. In addition, agricultural expansion caused an estimated 56‐65% of the available wetlands in Europe and North America to disappear. Globally, wetland loss is 26%, and still intensifying in many regions. Agricultural water withdrawal is largely attributed to irrigation. The key environmental issues for rivers related to unsustainable agriculture are: excessive water depletion, water quality reduction, waterlogging (60–80 million ha of irrigated lands are affected), salinization (20–30 million ha irrigated lands severely affected) and loss of ecosystem services (FAO, 1996). River downstream effects are temperature changes, depleted fish stock, effects on wetland, reduction in silt and water quality. The upstream effects are siltation, salinization and deforestation. Many countries and basins currently exploit their groundwater reserves at a rate substantially exceeding recharge. Overdraft occurs when pumping rates exceed the rate of natural recharge. Unsustainable groundwater use is often associated with irrigation, and can lead to both
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water scarcity and water quality problems. Postel (1999) draws on several sources to estimate total annual global groundwater overdraft at 163 km3. The threshold at which localized groundwater overdraft occurs at the whole‐basin level can be set at 0.55. The key impacts which result from overdraft are: increasing lifts and costs from the lowered water table, subsiding land (sometimes irreversibly damaging the aquifer) and degrading water quality (including saline intrusion and arsenic).
Water productivity is largely determined by crop yield in the agricultural sector, which dominates water use. Relatively small gains can be achieved by trending towards more beneficial water consumption. The greatest benefit comes from having a stable climate with adequate rainfall. Water productivity increased by at least 100% between 1961 and 2001, mainly due to increases in crop yields. Irrigated rice yields doubled and rainfed wheat yields rose by 160%. Globally, FAO (2003) estimated that water needs for food per capita halved between 1961 and 2001. A 10% increase in water productivity equals current domestic water consumption, therefore investing in agricultural water management is an attractive strategy for freeing water for other purposes. The water productivity of rice is significantly lower than that of other cereals, ranging from 0.15‐0.60 kilograms per cubic meter (kg/m3), while that of other cereals ranges from 0.20‐2.40 kg/m3. The average water productivity of other cereals in the developed world is 1.0 kg/m3, while in the developing world it is 0.56 kg/m3 (Rosegrant et al., 2002).
In many developing countries, industrial production and hence the sectoral use of water grow fast, putting increasing pressure on scarce water resources. The relationship between industrial water withdrawal and industrial growth is not linear, as technological advances lead to water savings and water reuse in industry. Hence industrial water withdrawals in many developed countries have flattened off, while industrial water consumption (which is only a fraction of the total water withdrawal) continues to grow. In terms of domestic water use, delivery of safe water and sanitation are critical. Withdrawals for domestic and industrial uses grew four‐fold between 1950 and 1995 (Cosgrove and Rijsberman, 2000; Shiklomanov, 1999). There is much promise in the ongoing developments for desalination technology, but today it contributes only 0.02% of global water withdrawals and perhaps 1% of drinking water (Martindale and Gleick, 2001). It is mostly limited to coastal regions. Three key issues are: high energy costs, concentrate disposal and high capital costs. Poverty is directly associated with lack of access to safe drinking water, sanitation and water‐related disease. Global sanitation coverage rose from 49% in 1990 to 58% in 2002 (WHO, 2004).15
15 Many people still access water and sanitation the same way their ancestors did thousands of years ago: 1 billion people lack access to improved water supply and 2.6 billion lack access to improved sanitation, resulting in water-related disease. There are four classes of water-related disease: 1) Waterborne, for which water is the agent of transmission, caused by pathogens transmitted from excreta to water to humans, e.g., cholera, hepatitis A and E; 2) Water-based, from hosts that either live in water or require water for part of their life cycle, e.g., schistosomiasis spreads in regions where irrigation and dam projects produce habitats that favor the host snails; 3) Water-washed, caused by water scarcity where people cannot wash themselves, their clothes or homes regularly, e.g., trachoma; and 4) Water-related insect vectors, e.g., malaria, onchocerciasis (UNEP, 2010). Water, sanitation and hygiene risk factors contribute annually to over 2 million deaths from diarrhea (cholera, typhoid) and over 1 million deaths from malaria.
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2.7. WATER QUALITY Water quality is affected by chemical, microbiological and thermal pollution (Mayers et al., 2009; UNEP, 2010): 1) Chemical contamination can occur as a result of excess nutrients, acidification16, salinity17, heavy metals and other trace elements18, persistent organic pollutants19 and changes in sediment loads. Anthropogenic substances can enter the environment through intentional, measured releases; as regulated or unregulated industrial and agricultural by‐products; through accidental spills or leaks during the manufacturing and storage of these chemicals; or as household waste. 2) Microbiological contaminants, bacteria, viruses and protozoa in water pose one of the leading global human health hazards. The greatest risk of microbial contamination comes from consuming water contaminated with pathogens from human or animal
16 Acidity of aquatic ecosystems (expressed as the pH value) determines their health and biological characteristics, disproportionately affecting young organisms. Most surface waters have a pH between 6 and 8.5; values below 6 can be hazardous to aquatic life. Lower pH can also mobilize metals from natural soils, e.g., aluminum, leading to additional stresses. Extensive acidification occurs downwind of power plants emitting nitrogen and sulfur dioxides, or downstream of mines releasing contaminated groundwater. Mining and power production can cause localized acidification of freshwater systems. Acid rain, a product of the interaction of emissions from fossil fuel combustion and atmospheric processes, can affect large regions (UNEP, 2010). 17 Freshwater plant and animal species typically do not tolerate high salinity, because it negatively impacts their metabolic function and oxygen saturation levels. Rising salinity can also alter riparian and emergent vegetation, affect the characteristics of natural wetlands and marshes, decrease habitat for some aquatic species, and reduce agricultural productivity and crop yields (Carr and Neary, 2008). Actions that can cause salinization include agricultural drainage from high-salt soils, groundwater discharge from oil and gas drilling or other pumping operations, industrial activities and certain municipal water-treatment operations. The chemical nature of the salts introduced by human activities may differ from those occurring naturally. 18 Trace elements, e.g., zinc, copper, arsenic and selenium, are naturally found in many waters. High natural concentrations of arsenic in groundwater are found in parts of Bangladesh and adjacent parts of India. Mining, industry and agriculture can lead to an increase in the mobilization of the trace elements out of soils or waste products into fresh waters. Even at extremely low concentrations, these materials can be toxic to aquatic organisms, impair growth, reproductive and other functions (UNEP, 2010). Heavy metals can accumulate in the tissues of humans and other organisms. Mercury and lead from industrial activities, landfills, commercial and artisanal mining also threaten human and ecosystem health in some areas. Emissions from coal-fired power plants are a major source of the mercury accumulating in the tissues of fish at the top of fish trophic levels (UNEP, 2008). Heavy metals also affect food quality, e.g., the preferential accumulation of cadmium in rice grain when effluent from zinc mines is used for irrigation. The United Nations Economic Commission for Europe finds that mining activities have severe impacts on water and the environment in eastern and South Eastern Europe, the Caucasus and central Asia. In some river basins, tailing dams for mining wastes also present substantial risks. 19 Diverse organic substances enter surface and groundwater through human activities, including pesticide use, industrial processes, and as degradation products of other chemicals (Carr and Neary, 2008). Numerous organic contaminants are persistent, bioaccumulative and toxic (PBT), are used globally and can be transported long ranges to regions where they have never been produced (UNEP, 2009b). For some compounds, non-lethal doses may be ingested by invertebrates and stored in their tissues. As larger organisms consume these prey species, PBT substances bioaccumulate, eventually to toxic levels. Certain pollutants break down over time, but degradation products may also be toxic. Pesticides leach into groundwater from agricultural runoff and urban landscapes. Insecticide DDT is banned in many countries, but still used for malaria control in Africa, Asia and Latin America (Jaga and Dharmani, 2003). It persists in the environment and resists complete microbial degradation. Even in countries where DDT is banned, it is still found in sediments, waterways and groundwater. Other PBT compounds are byproducts of industrial processes, e.g., dioxins, furans, and polychlorinated biphenyls (PCBs), which enter the environment through their use and disposal (UNEP, 1998). Oil and grease cause contact poisoning in aquatic organisms, coating and asphyxiation, behavioral changes, carcinogenic and mutagenic effects, e.g., petroleum products. Incomplete combustion of materials during manufacturing, incineration of waste or accidental fires produce polycyclic aromatic hydrocarbons and other mutagens and carcinogens which can leach into water (UNEP, 2008).
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feces.20 3) Altering natural water temperature cycles can impair biological functions, e.g., spawning, growth patterns, migration, and affect metabolic rates in aquatic organisms, leading to long‐term population declines. Warmer water dissolves less oxygen, impairing metabolic function and reducing fitness. Thermal impacts are severe downstream of thermal or nuclear power generation facilities or industrial activities (Carr and Neary, 2008). Multiple contaminants often combine synergistically to cause amplified, or different, impacts than the cumulative effects of pollutants considered separately (UNEP, 2010). Continued input of contaminants can ultimately exceed an ecosystem’s resilience, leading to dramatic and irreversible losses. The level of anthropogenic pollution is a function of the structure of a country’s economy and its institutional and legal capacity to address it. Groundwater systems are particularly vulnerable freshwater resources: once contaminated, they are difficult and costly to clean. Based on data availability and relevance to trends in biodiversity and human well‐being, the following three parameters of water quality are considered to be particularly useful: nitrate concentrations, biological oxygen demand and sediment loads in rivers/turbidity (UNEP, 2005). These three parameters are discussed in more detail below.
Eutrophication is a result of high‐nutrient loads (mainly phosphorus and nitrogen), which substantially impairs beneficial uses of water. Major nutrient sources include agricultural runoff, domestic sewage, industrial effluents and atmospheric inputs from fossil fuel burning and bush fires. Lakes and reservoirs are particularly susceptible to the negative impacts of eutrophication because of their complex dynamics, relatively longer water residence times and their role as an integrating sink for pollutants from their drainage basins (ILEC, 2005; Lääne et al., 2005). Eutrophic lakes frequently experience noxious algal blooms, increased aquatic plant growth and oxygen depletion, leading to degradation of their ecological, economic and aesthetic value by restricting use for fisheries, drinking water, industry and recreation (National Research Council, 1992). Nitrogen concentrations exceeding 5mg/L of water may indicate pollution from human and animal waste or fertilizer runoff from agricultural areas. Three macronutrients (nitrogen, phosphorus and potassium, NPK) and numerous micronutrients are required for plant growth. Crop production often requires NPK supplementation. N and P can travel beyond the field to which they are applied, potentially affecting ecosystems offsite. In addition, P in detergents and output from sewer systems contributes to aquatic plant growth near global population centers. Here, the focus is on N and P as drivers of ecosystem changes; K is not discussed, because it is relatively immobile and benign offsite. Consequences of increased emissions of NOx, NH3 and dissolved organic N compounds include: decreased drinking water quality (Spalding and Exner, 1993), eutrophication of freshwater ecosystems (McIsaac et al., 2001), hypoxia in coastal marine ecosystems (Rabalais, 2002). The potential health effects of nitrates in humans are numerous: methemoglobinemia (blue baby
20 Moreover, a number of pathogens are free-living in certain areas or represent IAS capable of colonizing a new environment, e.g., Vibrio bacteria and a few types of amoebas, which can cause major health problems: intestinal infections, amoebic encephalitis, amoebic meningitis (WHO, 2008); viruses and protozoa, including Cryptosporidium and Giardia, Guinea worm, etc (UNEP, 2010).
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syndrome), cancers, thyroid disruptions and birth defects (Carr and Neary, 2008). P compounds are the primary cause of most freshwater eutrophication and a component of estuarine eutrophication. In marine systems, excess P input causes harmful algal blooms21; growth of attached algae and macrophytes that damage benthic habitats, including coral reefs; deoxygenation and foul odors; fish mortality; and economic losses associated with increased costs of water purification and impairment of water supply for agriculture, industry and municipal consumption. Global warming may further exacerbate toxic blooms of cyanobacteria, because at higher temperatures they have a competitive advantage over other algae (Bates et al., 2008).
Organic materials from domestic wastewater treatment plants, food processing discharges and algal blooms, are decomposed by oxygen‐consuming microorganisms in water bodies, as measured by biochemical oxygen demand (BOD). Thermal stratification in nutrient‐enriched lakes with high BOD levels can produce conditions that allow nutrients and heavy metals in lake bottom sediments to re‐enter the water column. The eastern and southern coasts of North America, the southern coasts of China and Japan and large areas around Europe have undergone oxygen depletion. One of the world’s largest hypoxic or dead zones has appeared off the mouth of the Mississippi River in the Gulf of Mexico, attributed to excessive N loads from the river, with harmful impacts on biodiversity and fisheries (Rabalais et al., 2002). Projected food production needs and increasing wastewater effluents associated with an increasing population over the next three decades suggest a 10‐15% increase in the river input of N loads into coastal ecosystems, continuing the trend observed during 1970‐95 (MA, 2005). Human sewage and wastewater treatment are also significant sources of methane and N2O, potent greenhouse gases.
There are two primary drivers causing changes in the sediment loads of the rivers: 1) Catchment disturbance, which results in increased sediment loads. It is linked to unsustainable land use practices, e.g., deforestation, land clearance for agriculture, mining, mineral exploitation, construction and infrastructural development; 2) Dam construction, which results in sediment trapping and reduced sediment loads (Walling, 2009). Climate change may also affect sediment loads, but the distinction between climatic and other anthropogenic contributors is not always straightforward. Excessive sediment loads in rivers disturb the life‐cycle of fish, through interfering with breathing and impacting spawning areas. Deposited sediments can smother benthic organisms. Sediments also disturb nutrient cycles in wetlands, especially estuaries. Fine sediments adsorb nutrients and toxins, e.g., P, lead and pesticides, altering water chemistry (Carr and Neary, 2008). Significant reductions in natural loads are equally harmful by reducing nutrient availability downstream (UNEP, 2005). From the standpoint of ecosystem services, increased sediment loads also have implications for navigation and flood control. Reduced sediment input to a delta results in shoreline retreat, loss of land and increased coastal flooding (Walling, 2009).
3. Possible future developments in the domain of the driver
21 Cyanobacteria, also known as blue-green algae, have increased in freshwater and coastal systems, e.g., the East China Sea. The toxins produced by the excessive algal blooms are concentrated by filter-feeding bivalves, fish and other marine organisms. In humans, they can cause acute poisoning, skin irritation and gastrointestinal illnesses (e.g., shellfish poisoning).
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3.1. ECOSYSTEM SERVICES
Simulations by Alcamo et al. (2005) utilize the four MA scenarios (Global Orchestration, Order from Strength, Adapting Mosaic and TechnoGarden22) to estimate future worldwide ecosystem services. Results indicate that if agricultural practices are intensified, the side effects, e.g., contamination of groundwater or N transport to coastal zones, can limit the ecosystem services provided by groundwater, surface waters and the coastal zone, e.g., fishery, recreation. The scenarios project a much higher delivery of freshwater services to households and industry, especially in developing countries. The development of water infrastructure and delivery of clean water to households in developing countries can significantly reduce water‐related diseases. However, increased withdrawals can lead to large increases in wastewater, especially in Latin America (factor of 2 to 4) and Sub‐Saharan Africa (factor of 3.6 to 5.6) between 1995 and 2050. If wastewater is discharged untreated into surface waters and groundwater, it will pose a risk of contamination for society and reduce the habitat suitable for freshwater fish and other organisms.
Higher income makes it possible to deliver freshwater services to many more households
and industries in the future, but a consequence of increasing water withdrawals is a significant intensification of water stress throughout the developing world. Authors also point out that the global demand for fish grows, but it is questionable whether marine fisheries can keep up with this demand, even with an increase in aquaculture‐produced fish. Ecological limits make an increase in production unlikely in two out of the three important marine fisheries. Overall, these simulations raise a question about the reliability of future ecosystem services. They do not indicate the likelihood that thresholds or breaking points will be reached.
Within the MA scenarios, the highest per capita demand levels for food fish (17.3 kilograms) and production of 128 million tons by 2020 occur under Global Orchestration, due to rapid increases in urbanization and income growth. Under Order from Strength, rapid population growth combined with slower economic progress result in the lowest production increases, at 117 millions tons in 2020, corresponding to depressed per capita demand of 14.8 kilograms. The values for the other MA scenarios fall between these two extremes.
An improved understanding of the relationships between ecosystems and human well‐being is needed to facilitate sustainability. Further research is needed to better understand the connections among the production of multiple ecosystem services, the local and global impact of
22 Millennium Assessment considers the following four scenarios: 1) Global Orchestration, describing a globally connected society that focuses on global trade and economic liberalization. This society takes a reactive approach to ecosystem problems, but also takes strong steps to reduce poverty and inequality and to invest in public goods, e.g., infrastructure and education. 2) Order from Strength depicts a regionalized and fragmented world, concerned with security and protection, which emphasizes regional markets, paying little attention to public goods, and takes a reactive approach to ecosystem problems. 3) Adapting Mosaic chooses regional watershed-scale ecosystems as the focus of political and economic activity. Local institutions are strengthened and local ecosystem management strategies are common. Societies develop a strongly proactive approach to the management of ecosystems. 4) TechnoGarden is a globally connected world relying strongly on environmentally sound technology. This world uses highly managed, often engineered ecosystems to deliver ecosystem services, and takes a proactive approach to the management of ecosystems in an effort to avoid problems (Alcamo et al., 2005).
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ecological processes, and the determinants of ecological resilience (Alcamo et al., 2005). Our current lack of knowledge concerning the resilience of ecosystem services makes it difficult to assess the degree of concern. If ecosystems are relatively robust, it is possible that current trends may not greatly alter the provision of the more vital ecosystem services. By contrast, if ecosystems are relatively fragile and if the relationship between ecological impacts and ecosystem services is nonlinear, cumulative human impacts will some day push ecosystems over one or more thresholds, resulting in the collapse of a bundle of ecosystem services (Peterson et al., 2003). The true state probably lies between these two extremes and will differ for different ecosystem services. There are high levels of uncertainty concerning the relative magnitude of human impacts on ecosystems. Rates of habitat destruction and species extinctions are higher than they have ever been in the history of humanity (McNeill, 2000). Ecosystem services may be intricately linked to one another in surprising or unforeseen ways, e.g., deforestation can lead to the unexpected rise of a saline water table, severely affecting food production (Keating et al., 2002).
The type of ecosystem change that is of greatest concern involves regime shifts, which
occur when an entire system flips into an alternative stable state (Scheffer et al., 2001). These changes are a strongly nonlinear (accelerating, abrupt and/or irreversible) response to gradual changes in the variables that define a system’s stable state. Regime shifts in ecosystems cause rapid, substantial changes in ecosystem services. Ecological surprises are unexpected regime shifts, e.g. degradation of fisheries, coral reefs, quality of freshwater, emergence of disease and spread of nuisance species. Carpenter (2006) offers a reading list of ecological and socio‐ecological case studies of eco‐surprises. Increasing pressure on ecosystems will increase the frequency of regime shifts that affect ecosystem services and human well‐being. Ecological feedbacks may accentuate anthropogenic modifications of ecosystems. Changes in ecological functioning produced by unintended ecological feedbacks from human actions appear likely to amplify climate change, decrease agricultural productivity, reduce human health, and increase the vulnerability of ecosystems to IAS (MA, 2005). Research needs in the domain of ecological surprises include: data‐based risk analysis for thresholds that can be quantified, e.g., freshwater eutrophication, drought persistence in drylands; assessment of leading indicators that are grounded in empirical observation; practical, empirically confirmed guidelines for building resilience in sensible day‐to‐day decision‐making (Carpenter, 2006).
3.2. WATER RESOURCES
The primary direct drivers of degradation and loss of rivers, lakes, freshwater marshes and other inland wetlands include infrastructure development (e.g., dams), land conversion (e.g., deforestation), water withdrawal (e.g., irrigation), pollution (e.g., excess nutrients), overexploitation (e.g., overfishing, overgrazing) and the introduction of IAS. The primary indirect drivers of degradation and loss are population growth and increasing economic development. The primary direct driver of the loss and degradation of coastal wetlands, including saltwater marshes, mangroves, seagrass meadows and coral reefs is conversion to other land uses. Other direct drivers affecting coastal wetlands include diversion of freshwater flows, N loading, overharvesting, siltation, changes in water temperature and IAS. The primary indirect drivers of change are the population growth in coastal areas coupled with growing economic activity (MA, 2005).
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Most river‐related scenarios and projections for water use and water scarcity are obtained from global models that utilize a combination of climate and elevation data. These models do not supply the level of detail required to establish management options, assess threats or evaluate tradeoffs. More reliable information on actual stream and river discharge, and the amount of water withdrawn and consumed at the river basin level, would increase our ability to manage inland water ecosystems more efficiently, evaluate tradeoffs between different uses, and set conservation measures.
Lakes undergo seasonal changes and are continually modified through tectonic events or volcanic activity, landslides, erosion or wind. Understanding of lake water movement and potential productivity requires calculations of the lake depth and water volume. Estimates are often used, because the calculations require detailed knowledge of the lake bottom. Revenga and Kura (2003) specify the most common threats affecting lake ecosystems: toxic pollution, eutrophication, IAS, water level change and siltation.
Wetland ecosystem processes are driven by the complex coupling of climatic, soil and
biotic factors, which change quickly over space and time. Interactions between these processes promote the persistence of rare indigenous species and the maintenance of critical ecosystem functions that would disappear with the loss of the ephemeral and seasonal wetlands (Revenga and Kura, 2003). Sea level rise may affect a range of freshwater wetlands in low‐lying regions. In tropical regions, low lying floodplains and swamps may be displaced by salt water habitats due to the combined actions of sea level rise, more intense monsoonal rains and larger tidal/storm surges (Bayliss et al., 1997). This may dislocate or displace wetland flora and fauna. Flora not tolerant to increased salinity or inundation may be eliminated. Salt‐tolerant mangrove species could expand from nearby coastal habitats. Migratory and resident fauna, e.g., birds and fish, may lose resting, feeding and breeding grounds. Fish migrations may be affected by both temperature and flow patterns. The most apparent faunal changes may occur with migratory and nomadic bird species that use wetland habitats across or within continents (Walther et al., 2002). Changed rainfall and flooding patterns across arid land may adversely affect bird species that rely on a network of wetlands and lakes that are alternately or episodically wet and fresh or dry and saline (Roshier et al., 2001). The wetland carbon sink may also be affected by climate change, although the direction of the effect is uncertain due to the number of climate factors and possible responses.
Under the MA scenarios Order from Strength and Adapting Mosaic, wetland loss is
relatively slow in the short term, for different reasons. Reduction in international trade and direct investments limits new large‐scale water schemes. Within Adapting Mosaic, small‐scale and integrated water management projects are developed, which releases some pressure on wetlands. This is not the case in Global Orchestration. In TechnoGarden, technical improvements are expected. Some wetlands are allowed to decline, because their ecosystem services are provided by technological alternatives. For the second half of the period until 2050, in both Order from Strength and Global Orchestration, there is a long‐term increase of conversion to agricultural land use. For TechnoGarden and Adapting Mosaic, the technology and ecosystem management skills induce a restoration of wetlands. Climate change may put further pressure on wetlands in all scenarios. Sea level rise is expected to lead to loss of coastal wetlands, e.g., estuaries and deltas.
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This effect is most pronounced in Global Orchestration, Order from Strength, and Adapting Mosaic, where it may overcompensate for the effects of learning.
Based on the IPCC scenarios modified in Ramsar COP8‐Doc.11, by 2025 coastal wetlands
will experience loss due to sea level rise. Erosion of shorelines increases. The loss of wetlands and shore erosion is more extensive by 2100.
3.3. FLOODS AND DROUGHTS
Examination of evidence for the intensification of the global water cycle by Huntington (2006) reveals upward trends for the following variables: precipitation, runoff, tropospheric water vapor, soil moisture, glacier mass balance, evapotranspiration, growing season length and droughts, but no change in cloudiness, floods, tropical storm frequency and intensity. Substantial uncertainty regarding trends in hydro‐climatic variables remains because of differences in responses among variables and regions and major spatial and temporal limitations in data. There are large gaps in spatial coverage for some hydrologic indicators; therefore, trends in these areas are unknown.
Van Lanen et al. (2009) stress the importance of processes underlying the generation of
hydrological extremes for computations of flood and drought characteristics and trend prediction. Floods can be generated through intense and long‐lasting rainfall, snowmelt or flow obstruction, e.g., ice jam or landslide. Droughts can be caused either by low precipitation often combined with high evaporation losses, or result from precipitation being stored as snow. The authors also review the physical indices for large scale floods and for soil moisture, groundwater and streamflow droughts (Van Lanen et al., 2009). Climate change is expected to primarily affect precipitation, temperature and potential evapotranspiration, and is likely to affect the occurrence and severity of meteorological droughts. Changes in meteorological drought affect soil water drought and hydrological drought, i.e., groundwater and streamflow drought. Soil water drought is relevant for agriculture, terrestrial ecosystems, and health through the occurrence of heat waves. Hydrological drought impacts water resources, namely agriculture, domestic and industrial water use, aquatic ecosystems, power generation and navigation (Van Lanen et al., 2007).
Documented trends in floods show no evidence for a globally widespread change, despite increased media coverage, flood costs and flood risks. One study identified an apparent increase in the frequency of large floods (exceeding 100‐year return period levels) in 16 large basins across much of the globe during the 20th century (Milly et al., 2002). A global change detection study does not support the hypothesis of a global increase of annual maximum river flows23 (Kundzewicz et al., 2005).
23 The study finds increases in 27 cases, decreases in 31 cases and no trend in the remaining 137 cases of the
195 catchments examined worldwide. However, the overall maxima for the period (1961-2000) occur more frequently (46 times) in the later subperiod, 1981-2000, than in the earlier subperiod (24 times), 1961-80. Evidence is stronger for changes in the timing of floods, with increasing late fall and winter floods.
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Summaries of observed and predicted impacts of climate change on hydrologic droughts are available (Huntington, 2006; Van Lanen et al., 2007; Zhang et al., 2007). In the past three decades, droughts have become more widespread, more intense and more persistent due to decreased precipitation over land and rising temperatures, resulting in enhanced evapotranspiration and drying. The occurrence of droughts is determined largely by changes in sea surface temperatures, especially in the tropics, through changes in atmospheric circulation and precipitation. In the western United States, diminishing snow pack and resultant reductions in soil moisture also appear to be factors. In Australia and Europe, the extremely high temperatures and heat waves accompanying recent droughts imply direct links to global warming (Bates et al., 2008).
The IPCC scenarios modified in Ramsar COP8‐Doc.11 predict an increase in flood damage
by 2025 due to more intense precipitation events. By 2100, the flood damage becomes several times higher than in a “no climate change” scenario. Increased drought frequency is predicted for the period up to 2025, followed by further increase in drought events and their impacts by 2100.
Future projections of drought in the 21st century made using the Special Report on
Emissions Scenarios (SRES, Arnell, 2004) A2 emission scenario show regions of strong wetting and drying with a net overall global drying trend. This increase continues throughout the 21st century and by the 2090s the percentage of the land area in drought increases to 30%, 40% and 50% for extreme, severe and moderate drought, respectively. In all cases, as the severity of drought increases, the number of drought events and the duration of each decreases. In the future, the number of extreme and severe drought events is projected to double; for moderate drought, the number of events remains stable. There is a significant increase in the mean event duration for all forms of drought. The spatial distribution of changes in the PDSI over the 21st century was also explored. The model predicts drying over Amazonia, the United States, northern Africa, southern Europe and western Eurasia, and wetting over central Africa, eastern Asia and high northern latitudes (Burke et al., 2006).
EU Water and Global Change (WATCH) Integrated Project Work Block titled “Likely
Frequency, Severity and Scale of Future Extremes” will provide an analysis of droughts and large‐scale floods based on the global and regional scenarios for the 21st century as compared with the simulations for the 20th century. The Work Block report was not available by the deadline for this report.
The author of this report has found no global scenarios specifically addressing impacts of
floods and droughts on aquatic ecosystems and their services. It is possible to develop them by considering flood and drought characteristics relevant for the provision of services. Elements of flood and drought profiles that affect ecosystem services include: season/period; frequency; duration; flood depth and flood water quality. Ecosystem services that are likely to be impacted by flooding and droughts are: biodiversity maintenance; hydrological functioning; carbon sequestration and nutrient cycling. For drought conditions, Huxman et al. (2004) propose an evaluation of the ecosystem water use efficiency. Surprisingly, the low‐precipitation regions, e.g., deserts, are much more sensitive to changes in precipitation than expected. Moreover, during drought, total plant growth per unit of precipitation for tropical ecosystems approaches that of the
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most arid areas. For any ecosystem, the authors’ model predicts substantial reductions in productivity when rain falls below historical minimums.
3.4. BIODIVERSITY AND INVASIVE SPECIES Future extinction rates are projected to be five times higher for freshwater animals than
for terrestrial species (Ricciardi and Rasmussen, 1999). In addition to habitat loss, water quality and IAS, the following major threats to the biodiversity of freshwater ecosystems are identified by Revenga and Kura (2003): modification of river systems24, water scarcity25, the condition of inland water fisheries26 and climate change.27
MA (2005) offers scorecards for biodiversity developments until 2050, considering N‐S deposition, climate, IAS and land use. TechnoGarden and Adapting Mosaic scenarios are likely to see a decrease in the rate of biodiversity loss. In TechnoGarden, this is due to a significant reduction in land use change. In Adapting Mosaic, it is due to a reduction in IAS. Movements of IAS between countries also are reduced in Order from Strength, but the number of outbreaks within poorer countries is higher and the overall chance of IAS reaching richer countries is high. In the longer term, TechnoGarden bears the risk of significant technological failures that can lead to outbreaks of new pests and diseases. The worst‐case curve shows a peak in biodiversity loss midway through the period, which flattens out and declines after appropriate countermeasures are developed. In Adapting Mosaic, failed experiments and climate change might also increase the
24 Modifications of river systems aim to improve transportation, provide flood control, hydropower, more land and irrigation water, thereby boosting agriculture. Modifications include river embankments to improve navigation, drainage of wetlands for flood control and agriculture, construction of dams and irrigation channels, and the establishment of inter-basin connections and water transfers. The physical changes in the hydrological cycle disconnect rivers from their floodplains and wetlands and slow water velocity in riverine systems, converting them to a chain of connected reservoirs. This may impact the migratory patterns of fish species, alter the composition of riparian habitats, open up paths for exotic species, change coastal ecosystems and contribute to an overall loss of freshwater biodiversity (Revenga et al., 2000). Dams also affect the seasonal flow and sediment transport of rivers for an average of 160 kilometers downstream (Revenga and Kura, 2003). There are more than 45,000 large dams and an exponentially larger number of smaller dams on the world’s rivers. 25 Widespread depletion and pollution of surface and groundwater sources is expected to contribute to the global biodiversity loss. Diversions of river flow for irrigation and agricultural runoff cause a decline in species richness and a disappearance of valuable wetland habitats (Revenga and Kura, 2003). 26 Inland fisheries from rivers, lakes and other wetlands are a major source of protein for a large part of the world’s population, particularly the poor. Globally, inland fisheries landings increased at 2% per year from 1984 to 1997. In Asia, the rate is higher: 7% per year since 1992. This increase is a result of: 1) efforts to raise production above natural levels through fisheries enhancements (e.g., stocking and aquaculture) and 2) eutrophication of inland waters (FAO, 1999). Aquaculture practices may contribute to habitat degradation, pollution, introduction of IAS and the spread of pathogens (Naylor et al., 2000). 27 Warming of rivers will affect chemical and biological processes, reduce the amount of ice cover, reduce the amount of dissolved oxygen in deep waters, alter the mixing regimes and affect the growth rates, reproduction and distribution of organisms and species (Gitay et al., 2001). Species in small rivers and lakes are thought to be more susceptible to changes in temperature and precipitation than those in large rivers and lakes. Fish species distribution is expected to move towards the poles, with cold water fish being further restricted in their range, and cool and warm water fish expanding in range. Aquatic insects are less likely to be restricted given their aerial life stages. Less mobile fish and molluscs may be at higher risk due to their presumed inability to keep pace with the rate of change in freshwater habitats (Gitay et al., 2001). Warmer weather conditions are expected to facilitate the establishment of IAS. At high latitudes, warming is expected to increase biological productivity, whereas at low latitudes the boundaries between cold and cool-water species may change and possibly lead to extinctions (IPCC, 1996).
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rate of biodiversity loss in the longer term, albeit not as abruptly. The other two scenarios present a possibility of reducing the rate of loss on longer terms, which is more pronounced in Global Orchestration than in Order from Strength, and mainly in richer countries. Climate change might counteract the optimistic outlook for both Order from Strength and Global Orchestration.
Xenopoulos et al. (2005) build global scenarios of losses of riverine fish biodiversity. They
consider the known relationships between fish species and river discharge and combine them with a global hydrological model and two scenarios from the Intergovernmental Panel for Climate Change. In rivers with reduced discharge, up to 75% of local fish biodiversity would be headed toward extinction by 2070 because of combined changes in climate and water consumption. If fish are adapted to particular combinations of discharge and other habitat features, e.g., floodplains, stream gradient, substrate, riparian vegetation, which become decoupled under various human influences, then many more species will tend toward extinction. Other anthropogenic influences are likely to increase species loss above those reflected in the species‐discharge model: industrial pollution, eutrophication, physical modifications of rivers. Freshwater taxa are especially sensitive to the hydrologic changes indirectly related to increased CO2 emissions. Fish loss falls disproportionately on poor countries. Authors predict that reductions in water consumption can prevent many of the extinctions in these scenarios.
Sala et al. (2000) suggest that relative to terrestrial biomes, freshwater taxa are likely to
suffer more from land use changes and IAS than from climate, increased CO2 emissions and N deposition. Land use is expected to have especially large effects because humans live disproportionately near waterways and extensively modify riparian zones, inputting nutrients, sediments and contaminants. Biotic exchange is important because of extensive intentional and unintentional releases of organisms. The authors build three scenarios to estimate the total change in biodiversity to 2100, assuming no interactions, antagonistic or synergistic interactions among the drivers of change. Scenarios are not applied to freshwater biomes.
3.5. DEFORESTATION
Total global forest area continues to decrease, but the rate of net loss is slowing. Deforestation continues at a rate of 13 million ha per year. Forest planting, landscape restoration and natural expansion of forests have significantly reduced the net loss of forest area. The net change in forest area in the period 2000‐2005 is estimated at ‐7.3 million ha per year, down from ‐8.9 million ha per year in the period 1990‐2000. Africa and South America continue to have the largest net loss of forests. Oceania, North and Central America also have a net loss of forests. The forest area in Europe continues to expand, although at a slower rate. Asia reports a net gain of forests in the period 2000‐2005 after a loss during 1990‐2000 (FAO, 2005).
The four MA scenarios indicate that a total of 10‐20% of current grassland and forest area (warm mixed forests, tropical woodlands and tropical forests) may be lost by 2050, mostly because of the expansion of agricultural land (Alcamo et al., 2005). The global trends are a net result of slow reforestation in the temperate zones and strong deforestation in the tropical zones. Order from Strength exhibits the fastest rate of deforestation at the beginning of the scenario period, increasing from the historic annual rate of 0.4% to 0.6%. In Global Orchestration and Adapting
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Mosaic, the rate of loss of undisturbed forests is at the historic rate, and slightly below in Techno Garden. In industrial regions, forested areas generally expand from 2000‐2050, with the most growth expected under Global Orchestration and Techno Garden. Forests in developing regions decline, with the largest loss observed under Order from Strength.28
According to Bates et al. (2008), reduced deforestation conserves water resources, reduces
runoff, controls flooding, erosion, salinity and siltation, protects fisheries and hydroelectric power facilities. Currently, there are no global scenarios exploring the relationship between the forests and water resources. However, regional scenarios are available.29 A set of scenarios for Melbourne catchments considers bushfires along with a variety of clearing and thinning schemes to 2030. The Macaque model30 expects the water yield to increase due to the natural aging of the forests as they become re‐established after bushfires, even if there are no changes to the current timber‐harvesting regime (Battad et al., 2007; DSE, 2008). Impacts of forest disturbances on water quality are examined by Feikema et al. (2005) and Poynter and Featherston (2008).31
28 Overall, rapid depletion of forest areas continues under the Order from Strength scenario, while TechnoGarden expects an increase in net forest cover. Production of biofuel, particularly under the TechnoGarden scenario, is an important category of land use, especially in former Soviet countries, OECD and Latin America. The coverage of energy crops remains small, but it has a large influence on the trends in land use. Order from Strength continues to increase agricultural areas in sub-Saharan Africa and Latin America, due to a fast population growth and a limited potential to import food. The depletion of forests continues at a rate near the historic average, and slows down after 2050, because of slowing population growth. By 2050, 67% of the central African forest present in 1995 disappear. For Asia and Latin America, these numbers are 40% and 25%, respectively. In other regions, the rate of forest loss declines. 29 Odada et al. (2009) present plausible trends in land use change and resulting changes in lake levels and contribution of fisheries in the Lake Victoria basin across four scenarios to 2025. Scenarios with a low level of regional integration are the No Development Scenario (NDS) and Worst Case Scenario (WCS). The Current Practices Scenario (CPS) and Best Case Scenario (BCS) assume a high level of regional integration, including specific social, economic and environmental policies to nurture it. Increases in agricultural and urban land uses are observed in all scenarios, accompanied by a decline in forest land in all but the BCS. Deforestation is heaviest in WCS and lowest in BCS, occurring mainly in the frontier highlands of the basin, while extensive degradation under WCS and CPS centers around marginal lands closer to the lake. Water level variation shows a negative height variation trend. The key drivers propelling the water level trends are precipitation and other climate elements, agricultural land use, industrialization along the lake and energy demands. The challenges associated with WCS, which are countered in BCS with sustainable transboundary ecosystem management include: rapid population explosion; vulnerability to local and external environmental and economic shocks; unprecedented spread of AlDS, malaria; emergence of new diseases and re-emergence of old ones; and escalating poverty. 30 The Macaque model simulates physical processes within the catchment by examining variables associated with topography, vegetation, precipitation and temperature. It describes the relationship between water yield and time since disturbance, while considering variations in forest type and forest age. 31 The best management practices to address the potential impacts of timber harvesting on water quality include measures that minimize sediment generation and flow from unsealed roads and tracks. By comparison, sediment generation and flow from the harvested area are less significant and easier to manage (Poynter and Featherston, 2008). The impact of bushfires on the water quality in rivers is examined by Feikema et al. (2005). The study constructs and parameterizes models using the E2 catchment modeling framework to represent the flow, sediment and nutrient loads for the water storages and river systems in fire-affected catchments in eastern Victoria, Australia. The fire-affected catchments are predicted to deliver on average 27 times greater total suspended sediment loads, 4.9 times greater total nitrogen, and 7.9 times the amount of total phosphorus compared to pre-fire conditions. Sediment storage, adsorbed nutrients and recovery of the fire-affected areas are not represented in the model; therefore, observed increases in loads are likely to be lower.
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3.6. WATER AVAILABILITY, USE AND PRODUCTIVITY The focus here is on water availability, use, efficiency and productivity development guided by the following indicators. Water availability indicates the volume of water theoretically exploitable. Water withdrawals indicate the volume used by society to fulfill its domestic, industrial and agricultural needs. Water productivity indicates water availability for uses other than agriculture. The criticality ratio is an indicator of water scarcity stress at the basin level and the intensity of human water use. Water stress is defined as the long‐term average annual withdrawals to availability ratio (Alcamo and Henrichs, 2002).32 The change in water stress is an indirect indicator of the ability of a freshwater ecosystem to deliver ecosystem services. Return flows roughly indicate the magnitude of wastewater discharged into the receiving water in a river basin.
Rosegrant et al. (2002) discuss three scenarios projecting the likely water and food
outcomes to 2025: the business‐as‐usual (BAU), crisis (CRI) and sustainability (SUS) scenarios.33 Under BAU, total global water withdrawal in 2025 is projected to increase 22% above 1995 levels to 4,772 km3. This is consistent with other recent projections to 2025 including: Alcamo et al. (1998) medium scenario of 4,580 cubic km3, Seckler et al. (1998) business‐as‐usual scenario of 4,569 km3 and Shiklomanov (1999) forecast of 4,966 km3 (excluding reservoir evaporation). The Global Orchestration scenario shows strong economic growth coupled with an increase in population, which leads to a worldwide increase in withdrawals of around 40% by 2050. For OECD, MENA and FSU only slight increases in withdrawals are predicted, because economic and population growth are compensated by improving water efficiency. By 2050, TechnoGarden experiences strong structural changes in the domestic and industrial sectors and improvements in the efficiency of water use in all sectors, which lead to a net decrease in water withdrawals. Adapting Mosaic and Order from Strength do not have the largest economic growth, but by 2050,
32 Water stress is severe if the ratio is greater than 0.4; medium for ratios between 0.2 and 0.4; and low for ratios below 0.2. Alcamo and Henrichs (2002) identify critical regions in which water resources have higher sensitivity to global change than other regions, using an increase in water stress as a measure of watershed sensitivity. Stress increases when water withdrawals increase or water availability decreases. The extent of computed critical regions depends upon the scenario and the set of criteria for determining critical regions. Scenarios considered are: Markets First, Policy First, Security First and Sustainability First. Certain regions appear to be critical under all scenarios, i.e., central Mexico, the Middle East, large parts of the Indian subcontinent, and the northern coast of Africa. Oki et al. (2001) derive annual water availability from annual runoff estimated by land surface models using total runoff integrating pathways. The total population under water stress estimated for 1995 is consistent with earlier estimates. This number is highly dependent upon assumptions about the volume of water from upstream of a region, which is considered “available” water within the region. Therefore, it is necessary to evaluate the upstream regional water quality and the real consumption of water resources, as well as the accessibility of water. 33 The business-as-usual scenario (BAU) projects the likely water and food outcomes for a future trajectory based on the recent past, whereby current trends for water investments, water prices, and management are broadly maintained. The water crisis scenario (CRI) projects deterioration of current trends and policies in the water sector. The sustainable water use scenario (SUS) projects improvements in a wide range of water sector policies and trends (Rosegrant et al., 2002). An analogous set of three global scenarios has been prepared for World Water Vision (Gallopín and Rijsberman, 2000). The alternative scenarios are: the Business-as-Usual (BAU), representing the future trajectory if no major policy or lifestyle changes take place; the Economics, Technology and Private Sector (TEC), which relies on the market, the involvement of the private sector and technological solutions, and predominantly national/local or basin-level action; and the Values and Lifestyles scenario (VAL), that materializes through a revival of human values, strengthened international cooperation, heavy emphasis on education, increased solidarity and changes in lifestyles and behavior.
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they do have larger withdrawals than TechnoGarden. They show slow improvement in the efficiency of water use and fast population growth. Under CRI, unregulated and illegal withdrawals increase. After 2010, key aquifers begin to fail; declining water tables make extraction costs too high for continued pumping, causing a big drop in groundwater extraction, further reducing water availability for all uses. Under SUS, withdrawals decrease, leaving more water in‐stream for environmental purposes. Investments result in improved water use efficiency. Under CRI, water withdrawals result in sharply reduced environmental committed flow in 2025, 460 km3 globally. SUS results in higher environmental committed flows, with a global increase of 1,030 km3 (Alcamo et al., 2003; Rosegrant et al., 2002).
Global Orchestration predicts 18% of the world’s river basins are in severe water stress,
with 60% of the global population residing in these regions by 2050, or 4.9 billion people compared to current 2.3 billion. Under Adapting Mosaic and Order from Strength, the population increases to 5.3 and 5.5 billion, respectively. Under BAU, the criticality ratio increases globally from 0.08 in 1995 to 0.10 in 2025. Under SUS, allowable groundwater pumping in 2025 falls to 594 km3 representing a decline of 11% from the value in 1995 and a drop from the 2025 BAU value of 23%. Criticality ratios under CRI result in significantly higher ratios in 2025 than 1995, while SUS maintains 1995 levels. The ratio is relatively low globally and for large aggregated regions because abundant water in some countries masks scarcity in others, but the ratio is far higher for individual dry regions. It is in these dry regions the impact of SUS is most beneficial (Rosegrant et al., 2002).
By 2025, total worldwide water consumption under CRI is 13% (or 261 km3) higher than
that under BAU, while under SUS it is 20% (or 408 km3) lower. This reduction in consumption frees water for environmental uses. Under SUS, industrial water demand declines compared with BAU. Technological improvements in water use and recycling and increased water prices, which induce reductions in demand, are the cause. Under CRI, with weakened incentives and regulations and lower investment in technology, industrial water demand increases compared with BAU, as more water is needed to produce a unit of output. In 2025, total worldwide industrial water demand under CRI is 80 km3 (or 33%) higher than under BAU, while it is 85 km3 (or 35%) lower under SUS. Under CRI, global industrial water use intensity is 1.2 m3 per thousand U.S. dollars higher under CRI, and 1.3 m3 per thousand U.S. dollars lower under SUS (Rosegrant et al., 2002). By 2050, most scenarios predict an increase in efficiency with a net water availability increase in nearly all regions. Notable exceptions are MENA under BAU and CRI. From the perspective of ecosystem services, these results imply an increase in services delivered by freshwater systems.
A year‐to‐year variation in agricultural water productivity from 1995–2025 is likely caused by climate variability, which affects water availability and thus water productivity. The change of water consumption per hectare is small compared with the change of crop yield, which indicates the increase of water productivity results mainly from increases in crop yield. Water productivity of irrigated crops is higher than for rainfed crops in developing countries. Water productivity for rainfed crops is higher than for irrigated crops in developed countries for both rice and other cereals, which indicates favorable rainfall conditions for crop growth (Rosegrant et al., 2002).
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By 2025, water consumption under CRI is 13% higher than under BAU, while under SUS it is 20% lower. This reduction in consumption frees water for environmental uses. Virtually all the difference in water consumption between the CRI and BAU scenarios is in the irrigation sector. Under CRI, declining water use efficiency causes higher losses through non‐beneficial water consumption and greater water withdrawals. Compared with BAU, the 2025 global water withdrawal is 10% higher under CRI, while under SUS, it is 22% lower. Under CRI, beneficial irrigation water consumption is 8% lower than BAU in the developed world and 16% lower in the developing world. Under SUS, total irrigation consumption declined, but higher basin efficiency brought irrigation consumption close to BAU levels. Beneficial irrigation consumption under SUS is 2% lower than BAU in the developed world and 9% lower in developing countries (Rosegrant et al., 2002).
Low Groundwater pumping scenario (LGW) assumes that groundwater overdraft in all countries and regions using water unsustainably is phased out over 25 years beginning in 2000 by reducing annual groundwater pumping‐to‐recharge ratios to below 0.55 at the basin or country level. Under LGW, pumping in the overdrafting countries and regions declines by 163 km3. The projected increase in pumping for areas with more plentiful groundwater resources remains about the same as under BAU. Total global groundwater pumping falls to 753 km3 in 2021–2025, a decline from the 1995 value of 817 km3 and from the 2021–2025 BAU value of 922 km3 (Rosegrant et al., 2002).
Molden (2007) summarizes emerging trends in the water sector. Global food trade and consequent flows of virtual water (embodied in food exports) offer prospects for better national food security and relieving water stress. The changing climate affects temperatures and precipitation patterns, severely impacting tropical areas of intense poverty. Irrigators dependent on snow melt are even more vulnerable to changes in river flows. Urbanization increases demand for water, generates more wastewater and alters demands for agricultural products. Higher energy prices increase the costs of pumping water, applying fertilizers and transporting products, with implications for access to water and irrigation. Hydropower generation and agriculture compete for water resources. Greater reliance on bioenergy affects the production and prices of food crops and increases the amount of water used by agriculture. The Comprehensive Assessment estimates that in 2050 evapotranspiration necessary to support increased bioenergy use will approach total current depletion by agriculture. Perceptions about water are changing, as water professionals and policymakers realize the need to optimize the use of both blue and green water. More attention is paid to environmental flows and integrated approaches to water management. Available land and water resources can satisfy future food and fiber demands in several ways: 1) Rainfed scenario: investing to increase production in rainfed agriculture. An optimistic scenario assuming significant upgrades results in an increase of yields from 2.7 metric tons per ha in 2000 to 4.5 in 2050. Risks include low adoption rates and low yield improvements; 2) Irrigation scenario: investing in irrigation. Under optimistic assumptions, 75% of the additional food demand can be met by improving water productivity on existing irrigated lands. Alternatively, expansion requires 40% more withdrawals of water for agriculture. Irrigation could contribute 55% of the total value of food supply by 2050. Risks include degradation of aquatic ecosystems and capture
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fisheries; 3) Trade scenario: conducting agricultural trade within and between countries can mitigate scarcity, but poor countries depend on their national agriculture sector, and their purchasing power is low; 4) Reducing gross food demand by influencing diets, reducing post‐harvest losses (industrial and household waste); 5) The Comprehensive Assessment scenario combines elements of different approaches. Through appropriate investments in both irrigated and rainfed agriculture, by 2050 the cropped area will increase by 9% and water withdrawals for agriculture will increase by 13%. One challenge is to minimize the adverse impacts on ecosystem services (Molden, 2007).
Among the more comprehensive regional tools, a new computational model of the
Paraguay‐Paraná river basin (South America) is being designed to help local governments, farmers and ranchers: understand the factors that lead to water scarcity and impurity; make conservation‐friendly decisions about future land‐use projects; assess how landscape planning, water and soil conservation can improve water quality and sustain biodiversity downstream.34
3.7. WATER QUALITY With the exception of the TechnoGarden scenario, the MA scenarios show an increase in
global river N loading to coastal ecosystems ranging from 10% to 30% between 1995 and 2030. The TechoGarden scenario shows a 10% decrease because a high level of N removal from sewage is assumed and a lower level of NOx emissions and N deposition are computed for this scenario. All scenarios experience increase in the use of N and P fertilizers due to growing human population and increased food demand. Changes in nutrient use vary among the scenarios, depending on the key indirect drivers of food demand and technological change.
The four MA scenarios (2005) address eutrophication trends up to 2050. The technologies
developed in TechnoGarden are expected to reduce the risks of eutrophication, despite a rise in areas under agriculture, by reducing the impacts of agriculture, sewage and energy use. In Adapting Mosaic, better local management of agricultural runoff, fossil fuel burning and sewage will reduce the chances of eutrophication. These benefits may be offset by increasing use of fossil fuels and expansion in area under agricultural areas. Water quality in inland waterways may improve, but coastal eutrophication in densely populated areas will increase. Global Orchestration expects increases in eutrophication. Minimal population growth combined with technological advances increase energy and agriculture efficiency. However, improvements are moderate and do not address the nutrient runoff, resulting in an increase in nutrient pollution, especially in
34 The new tool is being developed by The Nature Conservancy in partnership with IBM, the University of Wisconsin’s Center for Sustainability and the Global Environment (SAGE), and Brazil's Water Agency and local institutions. Development around the Paraguay-Paraná river system is accelerating, with major agriculture and infrastructure projects planned for the near future. More than half of Brazil's extensive Cerrado grasslands have already been converted for ranching and agriculture, causing soil erosion and pollution. South America's largest city, São Paulo, is faced with the difficult task of supporting a population of 18 million with water resources threatened by upstream deforestation, sedimentation and pollution. The need to chemically treat water for São Paulo's residents rose 51% in the past five years. The modeling tool will explore questions about the relationship between changes in native vegetation and water quality; targeted native vegetation restoration to maximize improvement in water quality and flow; selection of national parks and protected areas in order to benefit river system integrity; and effects of different land uses on the integrity of each river. (The Nature Conservancy, 2010).
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poorer countries. The reactive management is too slow to address changes in soil and sediment P, setting up for eutrophication that is very difficult to reverse. Order from Strength is very vulnerable to increases in nutrient pollution, and areas of eutrophication greatly expand. There is little investment in environmental technology or management to offset substantial increases in agricultural area and fossil fuel use. In all scenarios, people have to cope with eutrophication caused by storage of P in soils and recycling of P from lake sediments.
The IPCC scenarios modified in Ramsar COP8‐Doc.11 predict lower water quality due to higher temperature by 2025, which is further altered by changes in water flow volume. By 2100, water quality effects are amplified.
Presently, it is not possible to compute global changes in water quality for the different scenarios. MA uses a concept of return flows as a surrogate variable for water quality. Return flows are the difference between withdrawals and consumption, and represent a rough estimate of the magnitude of wastewater discharged into the receiving water in a watershed. The type and concentration of water pollutants is different from different sources. For certain types of return flows, high rates of these flows may correspond to low water quality and high levels of water contamination and pressure on freshwater ecosystems. The adverse impact of return flows is greater for untreated flows. In OECD, the partial treatment of wastewater, i.e., removal of organic wastes and pathogens, is common. It is more uncertain whether agricultural return flows will be collected and treated because of the high costs of large volume collection and treatment. Wastewater treatment in poorer countries is now quite uncommon, except in cities.35 Water scarcity in rapidly expanding cities is projected to increase (Vörösmarty et al., 2000). Between 1995 and 2025, urban population doubles to 5 billion, and faces escalating water pollution and waterborne disease. Water supply and demand are driven by population growth and economic development, and to a lesser degree by climate.
An important source of uncertainty in estimating return flows is the uncertainty of the ratio
of consumption to withdrawals in different water use sectors. Also, the tools used to estimate the
35 By 2050, Global Orchestration experiences a 42% increase in global return flows, which follows an increase in water withdrawals. In OECD and the former Soviet countries population levels off and efficiency of water use improves, resulting in lower withdrawals and return flows. Furthermore, the richer societies maintain their environmental management efforts. Conversely, withdrawals and return flows substantially increase between 2000 and 2050 in sub Saharan Africa (factor of 3.7), Latin America (factor of 2), Asia (49%), and the MENA countries (24%). Under TechnoGarden, the trends up to 2050 are in the same direction as Global Orchestration. Stronger emphasis on improving water efficiency and somewhat lower economic growth rates lead to a stronger decrease in return flows up to 2050 in OECD (18%) and the former Soviet countries (43%), and to slower growth of return flows in sub-Saharan Africa (factor of 3.5), MENA (17%), and Asia (nearly 20%). The increase in Latin America is the same as for Global Orchestration (factor of two). In Adapting Mosaic, return flows decrease in the former Soviet Union because withdrawals decrease. In all other regions, return flows increase compared to Global Orchestration or TechnoGarden because of lower water use efficiency and larger population: sub-Saharan Africa (factor of 5.5), Latin America (factor of 2.6), Asia (76%), MENA (56%) and OECD (4%). Order from Strength has the largest withdrawals because of its slower improvement of the efficiency of water use and faster population growth. Return flows double worldwide between now and 2050. Increases by region are: former Soviet countries (9%), OECD (40%), Asia and MENA countries (approx. 100%), Latin America (factor of 3), and sub-Saharan Africa (factor of 4.7).
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indicators of ecosystem services of fresh water are too aggregated to include the role of local water policies and management. An emerging water quality concern is the impact of pharmaceuticals, e.g., antibiotics, painkillers, birth control pills and antidepressants, on aquatic ecosystems. Their long‐term impact on human or ecosystem health is poorly understood. Some compounds in personal care and household cleaning formulations are thought to be endocrine disruptors: they mimic natural hormones in humans and other species, e.g., nonylphenol ethoxylates36 (NPE). Endocrine disruptors may not be removed by existing wastewater treatment operations. Upon entering freshwater systems, these contaminants can feminize male fish and amphibians, cause thinning of eggshells in birds, inadequate parental behavior, cancerous growths, etc (Carr and Neary, 2008). Other pollutants which have only recently received attention include: plastics debris37; deicing fluids in tarmac runoff38; hydraulic fracturing (fracking) compositions39; aging and improperly maintained underground fuel tanks40; stormwater.41
36 Used in some detergents and industrial cleansers to lift surface dirt, NPE are believed to mimic estrogen. NPE residues are linked to hormonal disruption in fish and marine life. 37 There is a growing concern over the environmental impact of plastic debris on marine ecosystems, as well as public health risks stemming from consumption of contaminated seafood (Derraik, 2002). The deleterious effects of plastic debris on marine fauna include: entanglement in and ingestion of plastic litter, the use of plastic debris by IAS and the absorption of PCBs from ingested plastics. Bisphenol A (BPA) and other plastics additives are not chemically bound to plastics and over time leach into the environment. BPA is believed to be an endocrine disruptor. BPA is detectable in most samples of bottled and piped water. 38 During winter season, airports in snow covered regions spray large volumes of deicing chemicals onto airliners and allow the runoff to seep into nearby waterways. The two most often used compounds are ethylene glycol and propylene glycol. Deicing fluids can turn streams bright orange, lower oxygen levels in waterways and create dead zones for aquatic life. The environmental risk can be minimized by collecting and recycling the used fluid, applying the maximum dilution consistent with safety and by biological digestion, or eliminated by opting for infrared deicing. 39 One of the key environmental concerns surrounding the exploitation of coalbed methane (natural gas) is the use of chemicals in hydraulic fracturing. The process forces large volumes of water, mixed with sand and small amounts of chemicals, into the earth to break coal deposits and release gas. The chemicals used in the process may be responsible for groundwater contamination incidents in drilling areas. Investigations are impeded because the chemical compositions are proprietary trade secrets (USEPA, 2004b). 40 Gasoline is a complex contamination agent, which may originate from a variety of sources, e.g., underground fuel storage tanks in gas stations and large farms. In AlQassim region of Saudi Arabia, most of the existing gas stations are more than 25 years old. The technologies used for the construction of the stations and the underground gasoline tanks are outdated and do not meet international environmental standards. A statistical study by ElKholy et al. (2009) assesses the risks associated with soil and groundwater contamination due to gasoline leakage. Two gas stations are selected for a geoenvironmental investigation. An actual case of soil contamination due to gasoline leakage is confirmed; leaching into the groundwater resources is also possible. 41 In most countries, storm-generated runoff from agricultural and urban areas is the most important non-point pollutant source, e.g., nitrates in runoff and its accumulation in rivers. Point sources are becoming more controlled, e.g., urban sewage discharge. Non-point pollutant loads are becoming an increasing concern. USEPA (2010) notes that about 13% of U.S. rivers, 18% of lakes and 32% of estuaries are impaired by stormwater, i.e., they are rendered unsafe for swimming or fishing. In a natural system, rainwater soaks into the soil and is taken up by plants. The quick infiltration prevents the water from transporting contaminants and keeps waterways from eroding. In the urban environment, instead of soaking into the ground, rain runs across impervious surfaces, picking up contaminants along the way: metals, oil, organic waste, bacteria, etc. When the traveling stormwater hits a stream, it scours sediment, dislodges benthic invertebrates and erodes banks. Regulations need to define what is expected of developers, possibly by setting limits for stormwater volume or concentrations of contaminants. The rules may include guidelines for techniques such
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ACKNOWLEDGEMENTS
The author acknowledges UNESCO for supporting her work on this report. The author also wishes to acknowledge the valuable comments and suggestions made by William Cosgrove, Jerome Glenn and Gilberto Gallopín.
as infiltration basins, green roofs, rain barrels and rain gardens to capture runoff. Developers can also reduce impervious surfaces by constructing narrow roads and using porous pavement.
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