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<ul><li><p>Science of the Total Environment xxx (2013) xxxxxx</p><p>STOTEN-15234; No of Pages 10</p><p>Contents lists available at ScienceDirect</p><p>Science of the Total Environment</p><p>j ourna l homepage: www.e lsev ie r .com/ locate /sc i totenv</p><p>Impact of climate and land use change onwater availability and reservoirmanagement:Scenarios in the Upper Aragn River, Spanish Pyrenees</p><p>J.I. Lpez-Moreno a,, J. Zabalza a, S.M. Vicente-Serrano a, J. Revuelto a, M. Gilaberte a, C. Azorin-Molina a,E. Morn-Tejeda b, J.M. Garca-Ruiz a, C. Tague c</p><p>a Pyrenean Institute of Ecology, CSIC, Avda Montaana 1005, Zaragoza 50.059, Spainb C3I-Climate Change and Climate Impacts Unit, University Geneva, Bateille-D, Carouge, Geneva, Switzerlandc University of Santa Barbara, Bren School of Environmental Science &amp; Management, CA, USA</p><p>H I G H L I G H T S</p><p> First simulation of combined land cover and climate change in the hydrology of the Pyrenees First simulation of management of a Pyrenean reservoir under for future scenarios Deep hydrological changes are projected for the next future in the Pyrenees. Expected difficulties to supply water demand under obtained projections</p><p> Corresponding author. Tel.: +34 976 369393x880036E-mail address: nlopez@ipe.csic.es (J.I. Lpez-Moreno)</p><p>0048-9697/$ see front matter 2013 Elsevier B.V. All rihttp://dx.doi.org/10.1016/j.scitotenv.2013.09.031</p><p>Please cite this article as: Lpez-Moreno JI, etin the Upper Aragn River, Spanish..., Sci Tot</p><p>a b s t r a c t</p>a r t i c l e i n f o<p>Article history:Received 30 April 2013Received in revised form 9 September 2013Accepted 9 September 2013Available online xxxx</p><p>Editor: Damia Barcelo</p><p>Keywords:StreamflowClimate changeLand cover changeWater resourcesWater managementMediterranean mountains</p><p>Streamflows in a Mediterranean mountain basin in the central Spanish Pyrenees were projected under variousclimate and land use change scenarios. Streamflow series projected for 20212050 were used to simulate themanagement of the Yesa reservoir, which is critical to the downstream supply of irrigation and domesticwater. Streamflowswere simulated using the Regional Hydro-Ecologic Simulation System (RHESSys). The resultsshow that increased forest cover in the basin could decrease annual streamflow by 16%, mainly in early spring,summer and autumn. Regional climate models (RCMs) project a trend of warming and drying in the basin forthe period 20212050, which will cause a 13.8% decrease in annual streamflow, mainly in late spring and sum-mer. The combined effects of forest regeneration and climate change are expected to reduce annual streamflowsby 29.6%, with marked decreases affecting all months with the exception of January and February, when the de-cline will be moderate. Under these streamflow reduction scenarios it is expected that it will be difficult for theYesa reservoir to meet the current water demand, based on its current storage capacity (476 hm3). If the currentproject to enlarge the reservoir to a capacity of 1059 hm3 is completed, the potential to apply multi-annualstreamflow management, which will increase the feasibility of maintaining the current water supply. However,under future climate and land cover scenarios, reservoir storage will rarely exceed half of the expected capacity,and the river flows downstream of the reservoir is projected to be dramatically reduced.</p><p> 2013 Elsevier B.V. All rights reserved.</p><p>1. Introduction</p><p>Mediterranean mountains yield a large proportion of runoff at thebasin scale, and are key to ensuring water supply to downstream low-land areas (Viviroli et al., 2007; Garca-Ruiz et al., 2011). The need tooptimize the management of water generated in headwaters has ledto the construction of numerous dams to enable synchronization ofthe timing of runoff production and water demand. The Spanish Pyre-nees is a good example of this process, as the headwaters involved</p><p>..</p><p>ghts reserved.</p><p>al, Impact of climate and landal Environ (2013), http://dx.d</p><p>produce most of the surface water resources in the Ebro basin(Batalla et al., 2004; Lpez and Justribo, 2010; Lpez-Moreno et al.,2011), and they are regulated by many medium and large reservoirsto ensure thewater supply for agriculture, hydropower production, in-dustry, tourism and domestic uses in the semiarid lowlands of thebasin (Garca-Vera, 2013). In this area the reservoirs generally storewater from autumn to mid spring, and release water to downstreamareas and irrigation channels in late spring and summer, when waterdemand is higher (Lpez-Moreno et al., 2004, 2008). Exceptions tothis management regime are those dams that are also devoted to hy-dropower production, as these exhibit a double period of water releasein winter and summer, coinciding with peaks of energy demand(Lpez-Moreno and Garca-Ruiz, 2004).</p><p>use change onwater availability and reservoirmanagement: Scenariosoi.org/10.1016/j.scitotenv.2013.09.031</p><p>http://dx.doi.org/10.1016/j.scitotenv.2013.09.031mailto:nlopez@ipe.csic.eshttp://dx.doi.org/10.1016/j.scitotenv.2013.09.031http://www.sciencedirect.com/science/journal/00489697http://dx.doi.org/10.1016/j.scitotenv.2013.09.031</p></li><li><p>2 J.I. Lpez-Moreno et al. / Science of the Total Environment xxx (2013) xxxxxx</p><p>Scientists and water managers have observed with concern an al-most generalized decline in the runoff and water yield fromMediterra-nean rivers in recent decades (Garca-Ruiz et al., 2011, and referencestherein). Two explanations proposed for this trend are a shift in climaticconditions and changes in land cover because of land use changes. Anincrease in temperature, generally between 1 and 2 C, has been ob-served in the region since the beginning of the 20th century (Brunettiet al., 2004; Alpert et al., 2008), and in association with an increase inthe evaporative demand by the atmosphere, may have caused a de-crease in runoff (Lespinas et al., 2010; Liuzzo et al., 2010). A decreasein precipitation has also been identified as a cause of reduced runoff inmany Mediterranean basins (Garca-Ruiz et al., 2011). Thus, themagni-tude of the decrease in precipitation is amplified in themagnitude of de-crease in runoff (Ashofteh et al., 2013). For example, Zhang et al. (2009)quantified a 1525% decrease in runoff of the Yellow River as a conse-quence of a 10% decrease in precipitation. Voudoris et al. (2012) esti-mated that a decrease of b20% in precipitation in Crete would lead toa 2932% reduction in runoff. In mountainous areas the increased tem-perature has also caused a decrease in snow accumulation in mid andhigh altitude sites, which has often been amplified by negative trendsin winter precipitation. The result is an earlier onset of snowmelt anda decrease in the spring peak flows, with a consequent earlier start tothe water deficit period (Lpez-Moreno and Garca-Ruiz, 2004;Senatore et al., 2010). Land use change has also been identified as oneof the major environmental impacts in the Mediterranean headwatersin recent decades. In the European Mediterranean mountains the mostcharacteristic change has been a dramatic increase in the area coveredby shrubs and forest, which has occurred as a consequence of land aban-donment (Garca-Ruiz and Lana-Renault, 2011).</p><p>The Pyrenees is an outstanding example of the environmentalchanges noted above (Lpez-Moreno et al., 2008). In the last fivedecades, temperature has increased between 1 and 2 C (El Kenawyet al., 2012) and winter precipitation has decreased around 10%(Lpez-Moreno et al., 2011), leading to a decrease in snow accumula-tion in winter and spring (Lpez-Moreno, 2005). In addition, almost90% of the agricultural land in the mountains was abandoned in recentdecades, and natural revegetation has been accelerated by systematicafforestation works aimed at preventing erosion in highly degradedheadwaters (Lasanta, 1988; Lpez-Moreno et al., 2008). The result hasbeen a significant decrease in river discharges (Beguera et al., 2003;Gallart and Llorens, 2003; Lpez-Moreno et al., 2008) and runoff coeffi-cients (Lasanta et al., 2000; Garca-Ruiz et al., 2008; Lpez-Moreno et al.,2011), which have forced reservoir managers to reduce outflowsdownstream of dams throughout most of the year. This has enabledthe maintenance of (or in some cases an increase in) the amount ofwater diverted to irrigation channels and hydropower production(Lpez-Moreno et al., 2004).</p><p>The future sustainability of water demand in the region is uncertain,as theMediterranean area has been identified as one of the areasworld-wide most affected by climate change (Giorgi, 2006; Nogus-Bravoet al., 2008), and where runoff is expected to undergo a sharper decline(Milly et al., 2005; Nohara et al., 2006). Climate change is expected tohave substantial effects on the hydrological cycle in the Pyrenees(Majone et al., 2012; Garca-Vera, 2013). The observed revegetationprocess is far from complete, as many abandoned fields have not yetbeen colonized by forests, and an increase in temperature togetherwith a decrease in livestock pressure may lead to an increase in the for-est cover in the subalpine belt.</p><p>Although it is well known that climate and land use change interactin the evolution of runoff generation, both factors are generally studiedseparately (Tong et al., 2012). Thus, there are no reported studies thathave considered future water availability in the Pyrenees under a com-bination of projected trends in land cover and climatic conditions.</p><p>In this study, streamflows in the Upper Aragn River basin weresimulated using the Regional Hydro-Ecologic Simulation System(RHESSys) under the climatic and land cover conditions recorded</p><p>Please cite this article as: Lpez-Moreno JI, et al, Impact of climate and landin the Upper Aragn River, Spanish..., Sci Total Environ (2013), http://dx.d</p><p>in recent decades, and using a set of climatic and land cover scenariospredicted for the future. The selected case study is of particular inter-est as the basin drains to the Yesa reservoir, which is one of the mostimportant in the Pyrenees because it supplies water for irrigation tothe second largest irrigated area in the Ebro basin, andmore recentlyfor domestic use in Zaragoza, which is the largest city of the Ebrobasin (700,000 inhabitants). Lpez-Moreno et al. (2004) showedthat the decrease in runoff that has occurred in the upper Aragnbasin since 1960 has led to a dramatic reduction in outflows down-stream of the Yesa reservoir, affecting its capacity to satisfy the de-mand for irrigation water. It has also been shown that if similartrends continue it may not be possible to satisfy the current levelsof water demand. For this reason the Ebro River Administration Au-thority (Confederacin Hidrogrfica del Ebro CHE) has commencedwork to enlarge the Yesa dam, with the aim of more than doublingthe current storage capacity of the reservoir. Thus, the second objec-tive of this study was to simulate the management of the Yesa reser-voir based on its current capacity (479 hm3) and its projectedcapacity (1079 hm3) under various climate and land cover changescenarios. This will aid assessment of whether future water demandin the region can be met under changing environmental conditions.</p><p>2. Study area</p><p>The Upper Aragn River basin has an area of 2181 km2 (Fig. 1). Thehighest altitudes occur in the north of the basin (Collarada Peak,2886 m). The Aragn River flows northsouth across the Paleozoicarea (limestone, shale and clay), the Inner Sierras (limestone and sand-stone) and the flysch sector, then enters the Inner Depression (marls)and flows westward.</p><p>The average annual precipitation exceeds 1500 mm in thenorthernmost sector of the basin, and is approximately 800 mm inthe Inner Depression. The rainiest seasons are spring and autumn,although precipitation in winter is also substantial. Summer is gen-erally dry, with isolated rainstorm events caused by convective pro-cesses. The mean annual temperature of the basin is 10 C, and itincreases from north to south as a consequence of the decrease inaltitude to the south. At altitudes exceeding 1500 m a.s.l. snowcover is generally continuous from December to April, and lasts lon-ger in the higher altitude areas of the basin (Lpez-Moreno andGarca-Ruiz, 2004). River regimes reflect the distribution of the cli-matic characteristics, and the accumulation andmelting of the snow-pack. Long-term annual mean runoff is 915 hm3. Winter flow is lowas a consequence of the retention of precipitation as snow and ice,while the annual peak flow occurs in spring, coinciding with the an-nual peak rainfall and melting of the snowpack. The minimum riverflows occur in summer, but increase with the onset of autumn pre-cipitation. The differences between winter low flows and springpeak flows tend to diminish as the river reached the lower lyingareas of the basin, and hence snow covers a smaller percentage ofthe drained area (Lpez-Moreno and Garca-Ruiz, 2004).</p><p>Vegetation cover has been strongly impacted by human activities.Historically, cultivated areas have been located below 1600 m a.s.l.,in the valley bottoms, perched flats and steep, south-facing hill-slopes, whichweremanaged even under shifting agriculture systems(Lasanta, 1988). Forests (Pynus sylvestris, Pinus uncinata, Fagussylvatica, etc.) remain relatively well preserved on the northfacingslopes and everywhere between 1600 and 1800 m. Below this eleva-tion is also possible to find remaining natural forests of Quercuspyrenaica. The sub-alpine belt (up to 2200 m) was extensivelyburnt during the Middle Ages to increase the pasture areas. Duringthe 20th century, most cultivated fields were abandoned, except inthe valley bottoms. Abandoned fields, which represent about 25%of the total area, have been affected by a natural process of plantrecolonization, particularly with Buxus sempervirens, Genista scorpi-us, Rosa gr. Canina, Juniperus communis and Echinospartum horridum</p><p>use change onwater availability and reservoirmanagement: Scenariosoi.org/10.1016/j.scitotenv.2013.09.031</p><p>http://dx.doi.org/10.1016/j.scitotenv.2013.09.031</p></li><li><p>Fig. 1. Location and topography of the Upper Aragn River basin, including the distribution of the main streams in the basin.</p><p>3J.I. Lpez-Moreno et al. / Science of the Total Environment xxx (2013) xxxxxx</p><p>(Vicente-Serrano et al., 2006), or have been reforested with Pinuslaricio and Pinus sylvestris.</p><p>3. Data and methods</p><p>3.1. Climatic and hydrological data</p><p>Daily precipitation and temperature data were recorded at 14 sta-tions located in the Ebro basin or adjacent areas (Fig. 1) between 1975and 2006. The data, collected andmanaged by the Spanish Meteorolog-ical Agency (AEMet), were subject to checking a multistep approach ofquality control, reconstruction and homogenization (Vicente-Serranoet al., 2010; El Kenawy et al., 2012).</p><p>Information on reservoir storage fluctuations, inflows and outflowswere provided by the Ebro Basin Administration Authority (CHE). Theoutflow downstream of the reservoir was calculated by adding the out-flow from the Aragn River recorded immediately downstream of thedam to the volume of wate...</p></li></ul>

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