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DISCUSSION PAPER WATER GLOBAL PRACTICE Physical Impacts of Climate Change on Water Resources Fernando Miralles-Wilhelm, Leon Clarke, Mohamad Hejazi, Sonny Kim, Kelly Gustafson, Raul Muñoz-Castillo, and Neal Graham Water, Poverty, and the Economy Public Disclosure Authorized Public Disclosure Authorized Public Disclosure Authorized Public Disclosure Authorized

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Page 1: Physical Impacts of Climate Change on Water Resources€¦ · uses of water resources, and projecting river basins under water scarcity. The results of these simulations can also

D i s c u s s i o n P a P e rW a t e r G l o b a l P r a c t i c e

Physical Impacts of Climate Change on Water ResourcesFernando Miralles-Wilhelm, Leon Clarke, Mohamad Hejazi, Sonny Kim, Kelly Gustafson, Raul Muñoz-Castillo, and Neal Graham

Water, Poverty, and the Economy

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3 Introducing Commercial Finance into the Water Sector in Developing Countries

About the Water Global PracticeLaunched in 2014, the Word Bank Group's Water Global Practice brings together financing, knowledge, and implementation in one platform. By combining the Bank's global knowledge with country investments, this model generates more firepower for transformational solutions to help countries grow sustainably.

Please visit us at www.worldbank.org/water or follow us on Twitter at @WorldBankWater.

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Physical Impacts of Climate Change on Water ResourcesFernando Miralles-Wilhelm, Leon Clarke, Mohamad Hejazi, Sonny Kim, Kelly Gustafson, Raul Muñoz-Castillo, and Neal Graham

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© 2017 International Bank for Reconstruction and Development / The World Bank

1818 H Street NW, Washington, DC 20433Telephone: 202-473-1000; Internet: www.worldbank.org

This work is a product of the staff of The World Bank with external contributions. The findings, interpretations, and conclusions expressed in this work do not necessarily reflect the views of The World Bank, its Board of Executive Directors, or the governments they represent.

The World Bank does not guarantee the accuracy of the data included in this work. The boundaries, colors, denominations, and other information shown on any map in this work do not imply any judgment on the part of The World Bank concerning the legal status of any territory or the endorsement or acceptance of such boundaries.

Rights and Permissions

The material in this work is subject to copyright. Because The World Bank encourages dissemination of its knowledge, this work may be reproduced, in whole or in part, for noncommercial purposes as long as full attribution to this work is given.

Please cite the work as follows: Miralles-Wilhelm, Fernando, Leon Clarke, Mohamad Hejazi, Sonny Kim, Kelly Gustafson, Raul Muñoz-Castillo, and Neal Graham. 2017. “Physical Impacts of Climate Change on Water Resources.” Discussion Paper. World Bank, Washington, DC.

Any queries on rights and licenses, including subsidiary rights, should be addressed to World Bank Publications, The World Bank Group, 1818 H Street NW, Washington, DC 20433, USA; fax: 202-522-2625; e-mail: [email protected].

Cover design: Jean Franz, Franz & Company, Inc.

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iiiPhysical Impacts of Climate Change on Water Resources

Contents

Introduction 1Research Methods 3Results and Discussion 8Projected Volumetric Inflow 12Projected Water Scarcity 14The Socioeconomic Impacts of Future Development Scenarios on Water Scarcity 14Projected Effects of Mitigation Policies 18Conclusion 22Notes 23References 24

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1Physical Impacts of Climate Change on Water Resources

Abstract

T his paper documents an initial study focused on understanding the physical impacts of climate change on water resources throughout the world. The research performed in this study is based on the application of an Integrated Assessment Model to quantify these impacts for a wide range of scenarios of socioeconomic devel-

opment that offer a mix of possible futures for the availability, use, and management of water resources. Through this research and analysis, this study provides an integrated qualitative and quantitative understanding of the implications of several selected issues, including climate change and mitigation, and socioeconomic and technological develop-ments, on water scarcity and water-energy-food interactions in a global context. The understanding gained through this analysis is expected to contribute to the ongoing dialogue on the sustainability of multiple human activities and their trajectories toward global development pathways.

Introduction

Despite the well-recognized role of water in transmit-ting climate impacts to some of the growth drivers of the economy, the water sector has been largely ignored in climate change deliberations. The impacts are pro-jected to vary by region, and are likely to include changes in average hydroclimate patterns (precipita-tion, surface runoff, and stream flow), as well as increases in the probability of extreme events. Climate shocks are likely to impose higher costs than gradual changes in climate averages. Prudent management of water resources will be pivotal in addressing the cli-mate challenge—both for adapting to the effects of cli-mate change and for meeting global goals to mitigate greenhouse gases (GHG).

The precise consequences of climate change on the hydrological cycle are uncertain, which makes adaptation especially challenging. Uncertainty regarding impacts is partly a consequence of the limitations of climate models. Despite improvements in climate science, the Global Circulation Models (GCMs) developed to project climate futures generate a wide range of projections that often disagree on both the direction and magnitude of precip-itation changes. Furthermore, GCMs have not been designed to predict  changes in the hydrological cycle and lack the  precision required for planning and manag-ing water resources. These errors are compounded when projections are “downscaled” from regional to the finer spatial scales necessary for planning and the design of infrastructure. In addition, changes in the hydrological cycle imply that future water systems may not resemble the past (nonstationarity), so historic trends—as used in engineering designs—no longer serve as a reliable guide for assessing and managing future risks.

Identifying and analyzing the consequences of climate change in water resources requires integrated model-ing that allows proper incorporation of the potential impacts of climate in the hydrological cycle into all major sectors that use water, such as the urban, envi-ronment, agriculture, and energy sectors. It also

This discussion paper was authored by Fernando Miralles-Wilhelm, Earth System Science Interdisciplinary Center, University of Maryland; Leon Clarke, Joint Global Change Research Institute, Pacific Northwest National Laboratory and University of Maryland; Mohamad Hejazi, Joint Global Change Research Institute, Pacific Northwest National Laboratory and University of Maryland; Sonny Kim, Joint Global Change Research Institute, Pacific Northwest National Laboratory and University of Maryland; Kelly Gustafson, Department of Geographical Sciences, University of Maryland; Raul Muñoz-Castillo, Department of Geographical Sciences, University of Maryland; and Neal Graham, Department of Atmospheric and Oceanic Science, University of Maryland.

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2 Physical Impacts of Climate Change on Water Resources

requires the use of economic tools to determine the eco-nomic costs and benefits of dif-ferent adaptation strategies.

The use of Integrated Assessment Models (IAMs) to identify the physical impacts of climate change on water

resources has advanced greatly in the past decade. IAMs use a set of different assumptions and interre-lated factors simultaneously and include both physi-cal and social science models that consider demographic, political, and economic variables that affect greenhouse gas emission scenarios. IAMs allow researchers to explore interactions between sectors and to understand the potential ramifications of climate actions. Figure 1 illustrates a typical IAM.

FiguRe 1. A Typical integrated Assessment Model (iAM)

Human Earth Systems

Health

Transport

Managedecosystems

Technology

Food

Science

ENERGY

Security

Settlements

Population

Economy

Biogeophysical Earth Systems

CarbonCycle

Ecosystems

CoastalZones

Hydrology

Sea Ice

Oceans

AtmosphericChemistry

Earthsystemmodels

This paper aims to investigate the impacts of climate change on water resources throughout the world, and specific effects on water-dependent sectors of the economy, such as urban, energy, and agriculture sectors.

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3Physical Impacts of Climate Change on Water Resources

Research Methods

The analysis in this paper is conducted utilizing an IAM called the Global Change Assessment Model (GCAM) as the main analytical tool.1 The analysis involves setting up and running multiple GCAM sim-ulation scenarios to shed light on three important questions:

1. What are the physical impacts of climate change on  water scarcity around the world, and particu-larly on surface runoff?

2. What are the impacts of future development scenar-ios under consideration on water scarcity?

3. What are the impacts of implementing climate change mitigation on water scarcity?

To investigate the physical impacts of climate change on water scarcity, the results from multiple GCMs are used as inputs into GCAM, to assess the level of uncer-tainty propagating from climate models and their impli-cations on water scarcity conditions at the scale of individual countries. Three GCMs that span the range of uncertainty (wet, dry, and normal) are selected to drive the GCAM simulations, with and without accounting for the impacts of climate change on water availability. The results allow for a comparison between the uncertain-ties surrounding climate models and the corresponding distribution of water scarcity around the world.

Next, several Shared Socioeconomic Pathway scenar-ios (SSPs) are simulated, using hydrologic inputs from the GCMs, to show how socioeconomic and techno-logical development might affect water demands, and consequently water scarcity in different basins. SSPs describe potential future pathways for the evo-lution of key aspects of society that would affect our abilities to mitigate, and adapt to, climate change. Five SSPs were selected for this study that reflect a broad range of possibilities. The analysis focuses on quantifying regional water demands for different uses of water resources, and projecting river basins under water scarcity. The results of these simulations

can also be used to compare the relative effects of socioeconomic and technological changes to the effects of climate change.

Finally, the study examines the implications of limited water resources on energy and agricultural decisions. Simulations are carried out with and without con-straining water resources as a limited resource in water-using sectors (such as domestic water supply, energy, and agriculture). The results shed light on any changes in water demands by sector due to changes in water availability in the coming decades.

Using the Global Change Assessment Model (GCAM) to Quantify Impacts of Climate ChangeThe research questions posed in this paper are focused on quantifying the impacts of climate change, future development scenarios, and intervention policies on water resources throughout the world. This research also lays the groundwork for an analytical tool that can be used to support decisions not only in the scenarios documented in this paper, but other policy and interven-tion options that may be considered moving forward.

The methodological procedure used in this investi-gation can be summarized by the following major steps:

• A given climate model is selected as input, providing

spatial and temporal distributions of climate vari-

ables such as temperature and precipitation.

• These climate variables are used in GCAM to run its

water supply (hydrology) submodel (Hejazi et al.

2013, 2014a, 2014b).

• The GCAM numerical solution procedure is based on

a partial-equilibrium economics approach that is

documented in references such as Edmonds and

Reilly (1983), Brenkert et al. (2003), Kim et al. (2006),

and Clarke et al. (2007).

• GCAM outputs include water withdrawal

(demands) for each of the major water-using

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4 Physical Impacts of Climate Change on Water Resources

economic sectors (such as food production, energy

generation, and municipal supply); these outputs are

also used to calculate a water scarcity indicator (WSI).

• These outputs are generated for each one of the

modeling scenarios simulated in GCAM (including

the reference scenario, SSPs, mitigation scenario,

as discussed later in this paper).

A Brief Description of GCAMThe Global Change Assessment Model (GCAM) is an Integrated Assessment Model (IAM) for exploring consequences and responses to global change.2 Climate change is a global issue that impacts all regions of the world and all sectors of the global economy. Thus, any responses to the threat of cli-mate change, such as policies or international agree-ments to limit greenhouse gas emissions, can have wide-ranging consequences throughout the energy system, as well as on water resources, energy genera-tion, food production, land use, and land cover. IAMs endeavor to represent all world regions and all sec-tors of the economy in an economic framework in order to explore interactions between sectors and understand the potential ramifications of climate change mitigation actions.

A key advantage of GCAM over some other IAMs is that it is a Representative Concentration Pathway (RCP)-class model. This means it can be used to simulate sce-narios, policies, and emission targets from various sources, including the Intergovernmental Panel on Climate Change (IPCC).

GCAM is formulated in a dynamic-recursive modeling approach, with technology-rich representations of the economy, energy sector, land use, and water resources linked to climate models that can be used to explore climate change mitigation policies including carbon taxes, carbon trading, regulations, and accelerated deployment of energy technology (map  1). Regional population and labor productivity growth assumptions drive the energy and land-use systems, employing

numerous technology options to produce, transform, and provide energy services as well as to produce agri-culture and forest products, and to determine land use and land cover. Outputs of GCAM include projections of future energy supply and demand and the resulting greenhouse gas emissions; and radiative forcing and  climate effects of 16 greenhouse gases, aerosols, and short-lived species at 0.5×0.5 degree resolution— contingent on assumptions about future population, economy, technology, and climate mitigation policy. On the water side, six  major water use sectors are considered: agricultural irrigation, municipal water supply, primary resource extraction (energy/mining), livestock production, electricity generation, and indus-trial manufacturing.

Representative Concentration Pathways (RCPs)Representative concentration pathways are used to make assumptions about climate change mitigation levels. RCPs are four greenhouse gas concentration (not  emissions) trajectories adopted by the IPCC for its fifth Assessment Report (AR5) in 2014 (Moss et al. 2008). They describe four possible climate futures, all

MAP 1. gCAM Links economic, energy, Land-use, Water, and Climate Systems

32 energyregions

283 landregions

233 waterbasins

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5Physical Impacts of Climate Change on Water Resources

of which are considered possible depending on how much greenhouse gases are emitted in the years to come. The four RCPs—RCP2.6, RCP4.5, RCP6.0, and RCP8.5—are named after a possible range of radiative forcing values in the year 2100 relative to preindustrial values (increases of +2.6, +4.5, +6.0, and +8.5 W/m2, respectively) (Weyant et al. 2009).

The RCPs are consistent with a wide range of possi-ble  changes in future anthropogenic (man-made) GHG emissions. RCP2.6 assumes that global annual GHG emissions (measured in CO2-equivalents) peak between 2010 and 2020, with emissions declining substantially thereafter. Emissions in RCP4.5 peak around 2040, then decline. In RCP6.0, emissions peak around 2080, then decline. In RCP8.5, emis-sions continue to rise throughout the twenty-first century.

For the purposes of this study, a “no climate policy” reference scenario has been implemented in GCAM to reflect “reference” or baseline efforts toward climate mitigation. RCP4.5 is used as a “climate policy” sce-nario to reflect the implementation of climate mitiga-tion policies in GCAM simulations.

Water Scarcity IndexThe Water Scarcity Index (WSI) for a given GCAM sim-ulated scenario is determined as follows:

• Water demands (total water withdrawals) are simu-

lated in GCAM; these results are downscaled to the

grid scale and mapped up to country scale.

• The hydrology (water supply) module in GCAM is

used to generate runoff estimates using climate

information from the three GCMs—CCSM, GISS, and

FIO-ESM—at the basin level.3

• The surface runoff generated is mapped up to the

country scale.

• The total inflow into each country is calculated as

the sum of available surface runoff and groundwater

resources; groundwater data are obtained from the

FAO’s Aquastat database.4

• Runoff and inflow data are aggregated from monthly

to average annual estimates.

• The WSI for each country is calculated (annually) as:

WSI Demands

Runoff Inflow=

+

A water scarcity index value of 0.4 or higher (WSI ≥ 0.4) is used in this study to denote severe scarcity; (0.2 ≤ WSI < 0.4) denotes moderate scarcity; (0.1 ≤ WSI < 0.2) denotes low scarcity; and (WSI<0.1) denotes no scar-city, or abundant water resource availability in a coun-try as compared with water demands.

Global Climate Models (GCMs)For this study, three different Global Climate Models (GCMs) are selected to represent different climate model assumption and formulations, in an effort to provide a robust envelope of impacts of climate change on water resources and the corresponding analysis of results.

CCSM. The Community Climate System Model5 is a GCM  developed by the University Corporation for Atmospheric Research (UCAR). The coupled compo-nents include an atmospheric model (Community Atmosphere Model), a land-surface model (Community Land Model), an ocean model (Parallel Ocean Program), and a sea ice model (Community Sea Ice Model) (Hoffman 2006).

GISS. The Goddard Institute for Space Studies6 GCM is primarily aimed at the development of coupled atmo-sphere-ocean models for simulating Earth’s climate system. Primary emphasis is placed on investigation of climate sensitivity globally and regionally, including the climate system’s response to diverse forcings such as solar variability, volcanoes, anthropogenic and nat-ural emissions of greenhouse gases and aerosols, and paleoclimate changes. A major focus of GISS GCM

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6 Physical Impacts of Climate Change on Water Resources

simulations is to study the human impact on the cli-mate, as well as the effects of a changing climate on society and the environment.

FIO-ESM. The FIO Earth System Model7 is a GCM devel-oped by the First Institute of Oceanography in China. It includes an ocean surface wave model in addition to atmosphere, ocean, land, and ice components, and is coupled with a simulation model of the fully global car-bon cycle process and its interactions with the climate system. The historical simulation of the global carbon cycle follows the design of the CMIP5 (Climate Model Inter-comparison Project Phase 5) long-term simula-tion experiments.8 The simulation results are used to evaluate the performance of the model, including the atmosphere, ocean, land surface, and biogeochemical process of the ocean and terrestrial ecosystems.

Shared Socioeconomic Pathways (SSPs)Long-term scenarios play an important role in research on global environmental change. The climate change research community is developing new scenarios inte-grating future changes in climate and society to

investigate climate impacts as well as options for miti-gation and adaptation. One component of these new scenarios is a set of alternative futures of societal devel-opment known as the shared socioeconomic pathways (SSPs). The conceptual framework for the design and use of the SSPs calls for the development of global path-ways describing the future evolution of key aspects of society that would together imply a range of challenges for mitigating and adapting to climate change.

O’Neill et al. (2015) present the “SSP narratives,” a set of five qualitative descriptions of future changes in demo-graphics, human development, economy and lifestyle, policies and institutions, technology, and environment and natural resources. Development of the narratives drew on expert opinion to identify key determinants of these challenges that were essential to incorporate in the narratives, and combine these elements in the nar-ratives in a manner consistent with their interrelation-ships. The narratives are intended as a description of plausible future conditions at the level of large world regions that can serve as a basis for integrated scenar-ios of emissions and land use, as well as analyses of climate impact, adaptation, and vulnerability.

Within the conceptual framework for integrated sce-narios, the SSPs are designed to span a relevant range of uncertainty in societal futures. Unlike most global scenario exercises, the relevant uncertainty space that the SSPs are intended to span is defined primarily by the nature of the outcomes, rather than the inputs or elements that lead to these outcomes. Therefore, the SSP outcomes are specific combinations of socioeco-nomic challenges to mitigation and socioeconomic challenges to adaptation. That is, the SSPs are intended to describe worlds in which societal trends result in making mitigation of, or adaptation to, climate change harder or easier, without explicitly considering climate change itself. The SSPs used for this study are illus-trated in figure 2.

Figure 3 shows key assumptions made by the five SSPs of future global population, GDP, and GDP per capita, Source: adapted from O’Neill et al. 2015.

FiguRe 2. Shared Socioeconomic Pathways (SSPs) Representing Different Combinations of Challenges to Mitigation and Adaptation

Fossil-fueledDevelopment

Taking the Highway

(Mit. Challenges Dominate)SSP 5:

Regional RivalryA Rocky Road

(High Challenges)SSP 3:

Middle of the Road(Intermediate Challenges)

SSP 2:

SustainabilityTaking the Green Road

(Low Challenges)SSP 1:

InequalityA Road Divided

(Adapt. Challenges Dominate)SSP 4:

Socioeconomic challengesfor adaptation

Soci

oeco

nom

icch

alle

nges

for m

itiga

tion

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7Physical Impacts of Climate Change on Water Resources

FiguRe 3. global Population, gDP, and gDP per capita Made by each of the Five SSPs

14,000,000

a. Global population

Thou

sand

s

12,000,000

10,000,000

8,000,000

6,000,000

4,000,000

2,000,000

20052010

20152020

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20552060

20652070

20752080

20852090

2095210

00

RefSSP3

SSP1SSP4

SSP2SSP5

Figure continues next page

b. Global GDP

Mill

ion

1990

US$

500,000,000

450,000,000

400,000,000

350,000,000

300,000,000

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0

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2095210

0

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8 Physical Impacts of Climate Change on Water Resources

which were used as inputs for the GCAM simulations. Table 1 summarizes socioeconomic data assumed by the SSPs.

Results and Discussion

Estimates of total annual run-off volume for the three GCMs used in this study are shown in figure 4. This is the sum of the runoff generated for the 233 water basins around the world in GCAM. The figure shows that the three different climate models agree that

there is not a significant trend (upward or down-ward) of the total runoff volume generated; this

suggests that the amount of surface water globally will remain practically fixed throughout the coming decades.

These results underscore a main message that fresh-water is a finite resource with multiple uses, and thus requires careful management with due consideration of issues of water quality and efficiency.

While the total global runoff volume, an indicator of overall water availability may not vary significantly over the next decades, there are some variations worth noting among regions and countries.

Map 2 displays estimated runoff depth around the world, as predicted by the three GCMs for the year 2050 (maps showing changes to 2100 were generated,

FiguRe 3. continued

Note: Ref = reference scenario; SSP = Shared Socioeconomic Pathway.

c. Global GDP per capita

Thou

sand

s 199

0US$

/per

0

10,000

20,000

30,000

40,000

50,000

60,000

70,000

20052010

20152020

20252030

20352040

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2095210

0

RefSSP3

SSP1SSP4

SSP2SSP5

globally, total runoff volume is confidently estimated to remain relatively constant throughout the 21st century. However, runoff is likely to decline substantially in some countries and regions, including Russia, Central Asia, Central Africa, and the Middle east.

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9Physical Impacts of Climate Change on Water Resources

TAbLe 1. Shared Socioeconomic Pathways as implemented in gCAM

SSP1 SSP2 SSP3SSP4

SSP5High-income Medium-

income Low-income

Socioeconomics Population in 2100 6.9 billion 9 billion 12.7 billion 0.9 billion 2.0 billion 6.4 billion 7.4 billion

GDP per capita in 2100 $46,306 $33,307 $12,092 $123,244 $30,937 $7,388 $83,496

Fossil resources (technological change/acceptance)

Coal Med/Low Med/Med High/High Med/Low Med/Med Med/High High/High

Conventional gas and oil Med/Med Med/Med Med/Med High/Low High/Low High/Low High/High

Unconventional oil Low/Med Med/Med Med/Med Med/Low Med/Low Med/Low High/High

Electricity (technology cost)

Nuclear High Med High Low Low Low Med

Renewables Low Med High Low Low Low Med

CCS High Med Med Low Low Low Low

Fuel preference Renewables High Med Med High High High Med

Traditional biomass Low Low High Low Low High Low

Energy demand (service demands)

Buildings Low Med Low High Med Low High

Transportation Low Med Low High Med Low High

Industry Low Med Low High Med Low High

Agriculture and land use

Food demand High Med Low High Med Low High

Meat demand Low Med High Med Med Med High

Productivity growth High Med Low High Med Low High

Trade Global Global Global Regional Regional Local Global

SPA policy Afforestation Limited afforestation

No land policy

Pollutant emissions

Emissions factors Low Med High High High High Low

Note: Med = medium; SPA = [Shared Policy Assumption].

but are excluded for brevity). Runoff depth, measured as total runoff divided by total land area, provides a better means of comparing runoff trends among coun-tries than measuring runoff in water volume because it allows for large countries to be compared with smaller countries. Some trends can be summarized as follows:

• North America. There are no major variations in

runoff; the overall trend is for a small decrease in

runoff in Canada and the United States, but some

simulations (CCSM and GISS) project small increases

for the United States by 2050.

• Central America. There is a consistent trend toward

diminishing runoff across all three models. There is

significant disagreement between the models on run-

off in South America, with two of the three (CCSM and

FIO) predicting relatively stable runoff patterns

throughout the continent, but GISS predicting extreme

short falls in runoff in Brazil, Colombia, Ecuador, Peru,

and República Bolivariana de Venezuela.

• Europe and Central Asia. There is a consistent trend

toward lesser runoff in all model simulations, with

the Russian Federation showing a sharp decrease in

runoff in the second half of the century.

• East Asia. The runoff profile is relatively stable and

high (particularly in the Pacific). All simulations project

runoff decreases in China. Two (CCSM and GISS) out of

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10 Physical Impacts of Climate Change on Water Resources

FiguRe 4. estimates of global Runoff generation using the CCSM, FiO, and giSS Climate Models

Note: Global runoff generation reflects the sum for all countries. CCSM = Community Climate System Model; FIO-ESM = First Institute of Oceanography Earth System Model; GISS = Goddard Institute for Space Studies Model.

45,000

Tota

l ann

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uno�

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r)

40,000

35,000

30,000

25,000

20,000

15,000

10,000

5,000

1975 2000 2025 2050 2075 21000

CCSM GISSFIO ESM

MAP 2. Change in global Runoff by Country 2005–50mm/year

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a. CCSM (Community Climate System Model)

LegendModel: CCSM | Years: 2005–2050

> –200–200 – –100–100 – 00 – +100+100 – +200> +200

Change in Runo� (mm/yr)

Map continues next page

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11Physical Impacts of Climate Change on Water Resources

1 60°E

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LegendModel: GISS | Years: 2005–2050

< –200–200 – –100–100 – 00 – +100+100 – +200> +200

Change in Runo� (mm/yr)

b. GISS (Goddard institute for space studies) model

MAP 2. continued

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< –200–200 – –100–100 – 00 – +100+100 – +200

> +200

Change in Runo� (mm/yr)

c. FIO-ESM (First Institute of Oceanography Earth System Model)

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12 Physical Impacts of Climate Change on Water Resources

the three climate model simulations in GCAM show a

decreasing trend in runoff for Bangladesh, Cambodia,

Lao PDR, Myanmar, Thailand, and Vietnam.

• India. The results are mixed. Simulation results

for  South Asia show runoff projections for India

increasing during the second half of the century

when using the CCSM climate model as input. Using

the FIO as input results in a fairly stable runoff gen-

eration rate. Using GISS as climate model input

results in a slight decrease in runoff for India as early

as 2025 that continues in the second half of the

century.

• Middle East and North Africa. There is a consistent

trend toward decreasing runoff to the lower runoff

ranges. The Islamic Republic of Iran appears to be

somewhat of an exception; its runoff generation rate

is more or less stable (but still in the low range,

always below 200 mm/yr).

• Africa. There is a greater variation of runoff generation.

In the southern part of the continent, countries like

South Africa and Botswana show a consistent trend

toward lesser runoff. Countries in the lower latitudes

(20N to 20S) exhibit small variations in runoff

(less than +/- 100 mm/yr) in general. The GISS model

input produces larger decreases in runoff toward the

second half of the century in the Central African

Republic, the Democratic Republic of Congo, Malawi,

Mozambique, Tanzania, Zambia, and Zimbabwe.

Projected Volumetric Inflow

The rate of volumetric inflow into each country is pre-sented in map 3 for each of the climate models for the year 2050. Volumetric inflow accounts for streamflow

MAP 3. inflow Distribution by Country, 2050(km3/year)

180°160°E

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LegendModel: CCSM | Year: 2050Inflow (km3/yr)

0.00–10.0010.01–50.0050.01–100.00100.01–200.00200.01–500.00500.01–1000.001000.01–2000.00>2000

a. CCSM (Community Climate System Model)

Map continues next page

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13Physical Impacts of Climate Change on Water Resources

180°160°E

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LegendModel: GISS | Year: 2050Inflow (km3/yr)

0.00–10.0010.01–50.0050.01–100.00100.01–200.00200.01–500.00500.01–1000.001000.01–2000.00>2000

b. GISS (Goddard Institute for Space Studies) Model

MAP 3. continued

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c. FIO-ESM (First Institute of Oceanography Earth System Model)

LegendModel: FIO | Year: 2050Inflow (km3/yr)

0.00–10.0010.01–50.0050.01–100.00100.01–200.00200.01–500.00500.01–1000.001000.01–2000.00>2000.00

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14 Physical Impacts of Climate Change on Water Resources

in rivers crossing from one country to another, plus the contribution of groundwater storage within a basin (or country). Because of this, inflow is more of a hydraulic process than a hydrologic one. This means that the inflow flux is driven more by land surface fea-tures (such as soil type, land use, geology, and geo-morphology) than by climate (which has a primary influence on the rate of runoff generation through its relationship with rainfall and temperature); thus the results for inflow into countries show lesser depen-dence on the climate model used.

Projected Water Scarcity

Finally, the reference ( business-as-usual) scenario for these GCAM simulations is used to portray the current and future status of water stress/scarcity around the world without the introduction of climate mitigation

policies. Map 4 shows the sim-ulation results for the Water Scarcity Index (WSI) in the ref-erence scenario, comparing years 2005, 2025, 2050, and 2095.

These results illustrate three key trends in the WSI. First,

there is a general trend upward in water scarcity in the majority of countries of the world; this is reasonable to expect given increased pressure in water resources (increased demand) as a result of population growth, development, and other factors. Second, the WSI results appear to be fairly consistent across the three climate models used; this suggests that water scarcity is dominated by water demands rather than by the climate-influenced water availability (surface and groundwater). Finally, it appears that severe and mod-erate water scarcity around the world will increase sig-nificantly within the next few decades (between 2025 and 2050), particularly in countries such as China, India, and Mexico, and the Middle East and North Africa (MENA) region.

The Socioeconomic Impacts of Future Development Scenarios on Water Scarcity

In order to determine the socioeconomic impacts of future development scenarios on water scarcity, both the future supply and demand of water are estimated and compared, to determine regions where water scarcity may arise. Hydrologic inputs (supply) into the WSI calculation (runoff and inflows) come from the three GCMs used in the prior section, while water demands are dictated by the SSP scenarios simulated. These water demands are summarized in figure 5, broken down by water demand sector. SSP1 results in a curbing of water demand starting in the year 2050, and the decrease occurs across all demand sectors. SSP2 results show an increase in water demand fol-lowed by  a plateau toward 2070 and a very slight decrease in  water demand across all sectors toward the end of the simulation period in 2095. SSP3 results show, as  expected, a continuous increase in water demand across all sectors, with particular strong growth in irrigation water use. SSP4 results shows a water demand that plateaus starting in 2060, a similar trend to that found in SSP2. However, SSP4 stabilizes at lower  values than those in SSP2, reflecting the lesser energy generation and use of water in SSP4; increased efforts  for mitigation reduce the pressure over water resources.

This effect is further illustrated in figure 6, which displays total global water demand across the five SPs, as well as water demand for three select sectors: agriculture, electricity, and municipal use. Starting with total water use, the image shows that there is a very large plausible range of water demand by 2100, ranging from 4,500 billion km3/year for SSP1 to 6,500 billion km3/year for SSP3 and SSP5. This implies that future global demand for water is highly depen-dent on socioeconomic factors. For irrigation, the range is much tighter between the five SSPs, implying that socioeconomic factors will not play a large role in

global trends in water demand and water scarcity will be strongly affected by socioeconomic factors, with a significant majority of water going to irrigated agriculture.

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15Physical Impacts of Climate Change on Water Resources

Note: CCSM = Community Climate System Model; FIO = First Institute of Oceanography Earth System Model; GISS = Goddard Institute for Space Studies Model.

MAP 4. Water Scarcity indicator per Country

a. 2005 and 2025

CCSM

FIO

GISS

CCSM

FIO

GISS

b. 2050 and 2095

No scarcity Low scarcity Moderate scarcity Severe scarcity

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16 Physical Impacts of Climate Change on Water Resources

determining agricultural water use. Global water use for electricity generation, on the other hand, shows a  very large spread between SSP1 and SSP5, with a nearly 300 percent increase in water withdrawal predicted for the latter scenario over the former by

the year 2100. This is driven mostly by the assumption of a much larger size of the economy implicit in SSP5.

The relationship between the SSPs and the key water-us-ing sectors—energy and food—is illustrated in figure 10.

FiguRe 5. Water Demand (global Water Withdrawal) for the Five SSPs and broken Down by Major Water-using Sectorsbillion m3/year

Note: SSP = Shared Socioeconomic Pathway.

7,000

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al w

ater

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Socioeconomic challenges for adaptation

Soci

oeco

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halle

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itiga

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Municipal Primary energy Manufacturing Electricity Livestock Irrigation

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17Physical Impacts of Climate Change on Water Resources

Global generation of electricity tends to follow a similar pattern to that of the water demand for electricity shown in figure 6. The levels of energy production is signifi-cantly greater in SSP5 than in the other four scenarios, again because of the assumption of a much larger econ-omy. It is interesting to note that SSP1, SSP3, and SSP4 all predict similar levels of energy production throughout

the twenty- first century. However, as figure 6 shows, SSP1 predicts significantly less water consumption in the electricity sector than the other SSPs. Water demand for global food production tapers off and then declines in all scenarios (SSP1 and SSP5 circa 2050, SSP2 and SSP4 circa 2070) except for SSP3. This is mostly consistent with the irrigation water use trends shown in Figure 6.

FiguRe 6. Water Demand (global Water Withdrawal) across Five SSPs, by Sector

8,000

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c. Electricity d. Municipal

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18 Physical Impacts of Climate Change on Water Resources

Note: Ref = reference scenario; SSP = Shared Socioeconomic Pathway.

FiguRe 7. energy and Food Production at the global Scale for the Different SSPs

a. Global electricity generation b. Food production (crops)

EJ/y

r

Pca/

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Projected Effects of Mitigation Policies

Finally, two simulation scenar-ios are compared to determine the potential effects that miti-gation policies may have on future water scarcity. Under the “no mitigation policy” scenario (SSP1) water demand follows a trajectory that reaches 6.0 W/m2

in 2100, while water supply is calculated using climate scenario RCP6.0. Under a “mitigation policy” scenario (SSP1 with a mitigation policy), water demand follows a trajectory that reaches 4.5 W/m2 in 2100, while water supply is calculated using climate scenario RCP4.5.

Figure 8 shows the estimates of total annual runoff volume for the three GCMs used in this study, under a  climate mitigation policy scenario. When these results are compared to those presented in figure 4 for the GCAM reference scenario, the global amount of runoff generated is practically the same. The differ-ence in radiative forcing between implementing a

climate change mitigation policy (6.0 W/m2) and not (4.5 W/m2) is not large enough to result in a signifi-cant difference in total water supply. As in the results for the no mitigation policy case, implementing a cli-mate policy with RCP4.5 does not result in a signifi-cant trend (upward or downward) of the total runoff volume generated, suggesting that the amount of sur-face water globally remains practically fixed through-out the coming decades. Map 5 displays the spatial distribution of runoff depth around the world under a climate mitigation policy, showing some variations worth noting among regions and countries.

When there are no constraints on water demands, the results represent a response to changes only in demand and energy from the mitigation policy put in place. Since SSP1 is a sustainable scenario—and without a cli-mate policy the radiative forcing is 6.0 W/m2, while with the policy it is 4.5 W/m2—the difference in forcing is not large enough in this scenario and the results do not show a dramatic difference in total water demand (figure 9).

Simulations show that mitigation policies that reduce greenhouse gas concentrations throughout the 21st century will have little impact on water scarcity.

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19Physical Impacts of Climate Change on Water Resources

FiguRe 8. estimates of global Runoff generation using the CCSM, FiO, and giSS Climate Models under a Climate Mitigation Policybillion m3/year

Note: The estimates include the sum for all countries. CCSM = Community Climate System Model; FIO-ESM = First Institute of Oceanography Earth System Model; GISS = Goddard Institute for Space Studies Model.

45,000

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l ann

ual r

unof

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1975 2000 2025 2050 2075 21000

CCSM GISSFIO ESM

MAP 5. Distribution of Changes in global Runoff by Country, under a Climate Mitigation Policy, Projected using Climate Models CCSM, giSS, and FiO, Year 2050,mm/year

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LegendModel: CCSM | Year: 2050Runoff (mm/yr)

0.00–50.0050.01–100.00100.01–200.00200.01–300.00300.01–500.00500.01–700.00700.01–1000.00>1000

a. CCSM (Community Climate System Model)

Map continues next page

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20 Physical Impacts of Climate Change on Water Resources

Note: CCSM = Community Climate System Model; FIO-ESM = First Institute of Oceanography Earth System Model; GISS = Goddard Institute for Space Studies Model.

180°160°E

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c. FIO-ESM (First institute of oceanography earth system model)

LegendModel: FIO | Year: 2050Runoff (mm/yr)

0.00–50.0050.01–100.00100.01–200.00200.01–300.00300.01–500.00500.01–700.00700.01–1000.00>1000

MAP 5. continued

180°160°E

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LegendModel: GISS | Year: 2050Runoff (mm/yr)

0.00–50.0050.01–100.00100.01–200.00200.01–300.00300.01–500.00500.01–700.00700.01–1000.00>1000

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21Physical Impacts of Climate Change on Water Resources

FiguRe 9. global Water Withdrawal under SSP1 in Mitigation Policy and a No Mitigation Policy Scenarios

Note: SSP = Shared Socioeconomic Pathway.

0

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USATaiwanSoutheast AsiaSouth KoreaSouth AsiaSouth America_SouthernSouth America_NorthernSouth Africa

RussiaPakistanMiddle EastMexicoJapanIndonesiaIndiaEuropean Free TradeAssociation

Europe_Non_EUEurope_EasternEU-15EU-12ColombiaChinaCentral AsiaCentral America andCaribbean

CanadaBrazilAustralia_NZArgentinaAfrica_WesternAfrica_SouthernAfrica_NorthernAfrica_Eastern

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22 Physical Impacts of Climate Change on Water Resources

Global water withdrawals actually decrease slightly with the mitigation policy implemented, but some regions of the world decrease while others increase, as is shown in figure 10. China and India see significant increases in water use as a result of the mitigation pol-icy, while the rest of South Asia (excluding India), Western Africa, much of North America (Mexico, United States), and Central America and the Caribbean see the largest decreases in water withdrawal.

Conclusion

This paper documents an initial study focused on understanding the physical impacts of climate change on water resources throughout the world. The research performed in this paper is based on the application of an IAM (GCAM) to quantify these impacts for a wide range of scenarios of socioeconomic development that offer a mix of possible futures for the availability, use,

Note: Difference = No mitigation policy (Reference) – Mitigation policy. EU = European Union.

FiguRe 10. Difference in global Water Withdrawal under SSP1 between Mitigation Policy and No Mitigation Policy Scenarios for the 32 gCAM Regions

–40

–20

0

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Di�e

renc

e in

regi

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er w

ithdr

awal

(bill

ion

m3 /

yr)

Africa_EasternAfrica_NorthernAfrica_SouthernAfrica_WesternArgentinaAustralia_NZBrazilCanadaCentral America and CaribbeanCentral AsiaChinaColombiaEU-12EU-15Europe_EasternEurope_Non_EUEuropean Free Trade AssociationIndiaIndonesiaJapanMexicoMiddle EastPakistanRussiaSouth AfricaSouth America_NorthernSouth America_SouthernSouth AsiaSouth KoreaSoutheast AsiaTaiwanUSA

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23Physical Impacts of Climate Change on Water Resources

and management of water resources. The understand-ing gained through this analysis is expected to contrib-ute to the ongoing dialogue on the sustainability of multiple human activities and their trajectories toward global development pathways.

Through this research and analysis, this study pro-vides an integrated qualitative and quantitative understanding of the implications of several selected issues, including climate change and mitigation, socioeconomic and technological developments on water scarcity, and water-energy-food interactions in a global context.

A key message that follows from these results is that, at a global scale, the rate of runoff generation will not vary significantly over this century. These results reinforce the notion that freshwater is a finite resource with multiple uses, requiring careful man-agement with due consideration of issues of water quality and efficiency. While the global runoff vol-ume may not vary significantly over the coming decades some variations are worth noting among regions and countries.

Simulation results show a general upward trend in water scarcity in the majority of the world’s countries; this is reasonable to expect given increased pressure on water resources (increased demand) as a result of population growth, development, and other factors. These Water Scarcity Index results appear to be fairly consistent among the three climate models used, sug-gesting that water scarcity is dominated by water demands rather than by the climate-influenced water availability (surface and groundwater). Severe and moderate water scarcity around the world is likely to advance significantly between 2025 and 2050, in coun-tries and regions where water is already somewhat scarce, such as China, India, Mexico, and the Middle East and North Africa.

Implementing climate change mitigation policies (emissions reduction) results in a slight decrease in

global water withdrawals, but some regions of the world decrease while others increase.

Data on future projections of water supply and demand for different climate and socioeconomic development scenarios generated through this study need to be val-idated at the regional and country levels so they can provide reliable intelligence for purposes of water resources assessment and management.

IAMs such as GCAM provide a quantitative economic framework for an integrated analysis of water supply and demand, multiple demand sectors, climate inputs, and other forcing factors such as land use change, policy interventions, and technological developments. These models provide a viable tool to explore addi-tional issues related to the water-energy-food nexus. Further research can be focused on such issues as the implications of groundwater availability and changes in pumping costs on future water supply and its effect on urban services, energy, and food security; the repercus-sions of removing existing distortions (subsidies) in water availability and distribution in the future; the economic costs of noncooperation across basins/coun-tries/regions and the potential benefits of cooperation; quantifying trade-offs in water availability and its impact on major economic sectors; defining effective adaptation strategies/investments that are necessary to mitigate the impact of climate change on water scarcity and stress; and identifying and planning key invest-ments at regional and country levels to address eco-nomic water scarcity.

Notes

1. http://www.globalchange.umd.edu/models/gcam.

2. GCAM is a publicly available, open source modeling tool, developed and  maintained by the Pacific Northwest National Laboratory, part of  the US Department of Energy. It is available at http://www . globalchange .umd.edu/models/gcam/download/. Further details about GCAM can be found on its wiki site: https://wiki.umd.edu/gcam.

3. CCSM = Community Climate System Model; FIO-ESM = First Institute of Oceanography Earth System Model; GISS = Goddard Institute for Space Studies Model.

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4. http://www.fao.org/nr/water/aquastat/main/index.stm.

5. http://www.cesm.ucar.edu/about/.

6. http://www.giss.nasa.gov/projects/gcm/.

7. http://cclics.rcec.sinica.edu.tw/xms/content/show.php?id=3429.

8. http://cmip-pcmdi.llnl.gov/cmip5/.

References

Brenkert, M., S. J. Smith, S. Kim, and H. Pitcher. 2003. “Model Documentation for the MiniCAMRep.” PacificNorthwest National Laboratory, Richland, WA.

Clarke, L., J. Lurz, M. Wise, J. Edmonds, S. Kim, H. Pitcher, and S.  J.  Smith. 2007. “Model Documentation for the MiniCAM Climate Change Science Program Stabilization ScenariosRep.” Pacific Northwest National Laboratory Richland, WA.

Edmonds, J., and J. Reilly. 1983. “A Long-term, Global, Energy-Economic Model of Carbon Dioxide Release From Fossil Fuel Use.” Energy Economics 5 (2): 74–88.

Hejazi, M., J. Edmonds, V. Chaturvedi, E. Davies, and J. Eom. 2013. ”Scenarios of Global Municipal Water-use Demand Projections over the 21st Century.” Hydrological Sciences Journal 58 (3): 1–20.

Hejazi, M. I., J. Edmonds, L. Clarke, P. Kyle, E. Davies, V. Chaturvedi, M. Wise, P. Patel, J. Eom, and K. Calvin. 2014a. “Integrated Assessment of Global Water Scarcity over the 21st Century under Multiple Climate Change Mitigation Policies.” Hydrology and Earth System Sciences 18: 2859–83. doi:10.5194/hess-18-2859-.

Hejazi, M., J. Edmonds, L. Clarke, P. Kyle, E. Davies, V. Chaturvedi, M. Wise, P. Patel, J. Eom, K. Calvin, R. Moss, and S. Kim. 2014b. “Long-term Global

Water Projections using Six Socioeconomic Scenarios in an Integrated Assessment Modeling Framework.” Technological Forecasting and Social Change 81 (January): 205–26. http://dx.doi.org/10.1016/j.techfore .2013.05.006.

Hoffman, F. 2006. “Terrestrial Biogeochemistry in the Community Climate System Model (CCSM).” Journal of Physics: Conference Series 46 (2006): 363–69.

Kim, S., J. Edmonds, J. Lurz, S. Smith, and M. Wise. 2006., “The Object-oriented Energy Climate Technology Systems (ObjECTS) Framework and Hybrid Modeling of Transportation in the MiniCAM Long-term, Global Integrated Assessment Model,” Energy Journal 27  (Special Issue, Hybrid Modeling of Energy-Environment Policies): 63–92.

Moss, R., M. Babiker, S. Brinkman, E. Calvo, T. Carter, J. Edmonds, I. Elgizouli, S. Emori, L. Erda, K. Hibbard, R. Jones, M. Kainuma, J. Kelleher, J. Lamarque, M. Manning, B. Matthews, J. Meehl, L. Meyer, J. Mitchell, N. Nakicenovic, B. O’Neill, R. Pichs, K. Riahi, S. Rose, P. Runci, R. Stouffer, D. van Vuuren, J. Weyant, T. Wilbanks, J. Ypersele, and M. Zurek, 2008. Towards New Scenarios for Analysis of Emissions, Climate Change, Impacts, and Response Strategies. Geneva: Intergovernmental Panel on Climate Change.

O’Neill, B., E. Kriegler, K. Ebi, E. Kemp-Benedict, K. Riahi, D.  Rothman, B. van Ruijven, D. van Vuuren, J. Birkmann, K. Kok, M. Levy, and W. Solecki. 2015. “The Roads Ahead: Narratives for Shared Socioeconomic Pathways Describing World Futures in the 21st Century.” Global Environmental. Change. http://dx.doi.org/10.1016 /j.gloenvcha.2015.01.004.

Weyant, J., C. Azar, M. Kainuma, J. Kejun, N. Nakicenovic, P. Shukla, E.  La Rovere, and G. Yohe. 2009. Report of 2.6 Versus 2.9 Watts/m2 RCPP  Evaluation Panel. Geneva: Intergovernmental Panel on Climate Change (IPCC) Secretariat.

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