Impact of climate and land use change on water availability and reservoir management: scenarios in the Upper Aragón River, Spanish Pyrenees

Assessing the climate change adaptability of sustainable land management practices regarding water availability and quality: A case study in the Sorraia catchment, Portugal

In Mediterranean catchments, such as the Sorraia catchment in Portugal, it is expected that climate change will increase drought stress and the deterioration of water quality in reservoirs. Sustainable land management (SLM) practices are seen as an adaption measure for those problems, but the effectiveness on improving climate change impacted water availability and quality on catchment scale is still poorly understood. Therefore, this study aims to evaluate the effectiveness of SLM practices in adapting the impacts of climate change on water availability and quality of the Montargil and Maranhão reservoirs in the Sorraia catchment. A well-calibrated Soil Water Assessment Tool model is used to simulate four scenarios (2041-2071 and 2071-2100; representative climate pathways 4.5 and 8.5), to investigate the effects of climate change on total phosphorus load (TP) in streams, reservoir volume, irrigation use and water exploitation index (WEI). Results showed that WEI will not exceed any water stress level while reservoir water quality will worsen. In particular since the TP load in streams flowing into the reservoirs increases and the volume decreases, it is likely that the existing P limitation for eutrophication will be counteracted. Nevertheless, tested SLM practices were able to decrease the TP load in those streams and increase the reservoir volume under future climates. Overall, this study shows that the SLM practices are effective in adapting to the climate change effects regarding reservoir water quality, without worsening the water availability; thus, it is a promising tool that should be investigated further for application by e.g. local land-users and decision makers.

Hydrological models for climate-based assessments at the watershed scale: A critical review of existing hydrologic and water quality models

Global changes, including climate and land use changes, can result in significant impact to water resources. Planning for these changes requires making projections, even in the face of considerable uncertainties, to make informed management and policy decisions. A number of climate change scenarios and projections at global and regional levels are available that can be used to predict the likely range of outcomes. However, there is a need to translate these projections into potential implications for hydrology and water quality. Since there are dozens of hydrologic models, there is a need to evaluate them critically and to develop guidance regarding selecting the appropriate model for a given objective. We conducted a review of 21 different models commonly used for modeling hydrology (8), water quality (6) or both (7) at the watershed scale. Six of the models are strictly water quality models that depend on a separate model or observed data for hydrology. Seven additional models are useful for estimating hydrology and water quality simultaneously. The models were then evaluated based on ten different criteria, including functionality, scope, ability to model extreme events, data requirements, availability, and technical support, among others. The models were ranked Low, Medium or High in each of the criteria. The results indicate that three hydrologic models, MIKE-SHE, HEC-HMS, and MODHMS, as well as two full hydrology and water quality models, SWAT and WARMF, stand out in terms of functionality, availability, applicability to a wide range of watersheds and scales, ease of implementation, and availability of support. Modelers should carefully select the best model for their application, in part guided by the criteria discussed herein.

Modelling climate change impacts at a drinking water reservoir in Turkey and implications for reservoir management in semi-arid regions

Climate change can have severe impacts on the water availability in semi-arid regions. In this study, we assessed the impact of climatic changes on water availability in the Altınapa Reservoir Watershed, located in the Konya province, south-central Turkey. Altınapa Reservoir supplies drinking water to Konya, a city of about 2 million population. We investigated possible changes in streamflow and reservoir storage over 2021-2098 under two representative concentration pathway scenarios (RCP4.5 and RCP8.5) developed based on GFDL-ESM2M, HadGEM2-ES, and MPI-ESM-MR global circulation models. We used a physically based model (SWAT-Soil and Water Assessment Tool) for understanding the hydrologic response of the basin to climatic changes. Results show that upward trends in air temperatures in the range of 0.01-0.04 °C/year and 0.005-0.06 °C/year are expected from 2021 to 2098 under the RCP4.5 and RCP8.5 scenarios, respectively. According to the HadGEM2-ES model, precipitation and streamflow would show a downward trend at a rate of 0.96 mm/year and 0.007 m³/s/year under the RCP4.5 scenario and at a rate of 1.62 mm/year and 0.01 m³/s/year under the RCP8.5 scenario, respectively. GFDL-ESM2M and MPI-ESM-MR models project upward trends in precipitation and streamflow under the RCP4.5 scenario (in the range of 0.64-1.28 mm/year and 0.0003-0.006 m³/s/year, respectively), and downward trends under the RCP8.5 scenario (in the range of 0.47-0.76 mm/year and 0.0015-0.003 m³/s/year, respectively). Reservoir storage is projected to increase slightly according to GFDL-ESM2M model and decrease according to the HadGEM2-ES, and MPI-ESM-MR models under both scenarios. Precipitation, streamflow, and reservoir storage predictions of GFDL-ESM2M and MPI-ESM-MR models are considerably lower than those observed in the basin in recent decades, showing that water resources will decrease in the future. The changes in water withdrawal patterns could cause further reductions in water availability. Good resilience to climate change can be achieved by a flexible water management system and by reducing water consumption and water losses in the watershed and from the reservoirs.

Integrated Modeling of Agronomic and Water Resources Management Scenarios in a Degraded Coastal Watershed (Almyros Basin, Magnesia, Greece)

The scope of this study is to assess the effects of agronomic and water resources management scenarios on groundwater balance, seawater intrusion, and nitrate pollution and the comparison of the developed scenarios relative to the current crop production and water management regime in the coastal agricultural Almyros basin in the Thessaly region, Greece. Agronomic and water resources scenarios have been simulated and analyzed for a period of 28 years, from 1991 to 2018. The analysis has been conducted with the use of an Integrated Modeling System for agricultural coastal watersheds, which consists of coupled and interlinked simulation models of surface water hydrology (UTHBAL), reservoir operation (UTHRL), agronomic/nitrate leaching model (REPIC), and groundwater models for the simulation of groundwater flow (MODFLOW) and contaminant transport of nitrates (MT3DMS) and chlorides (SEAWAT). The pressure on water resources has been estimated with the Water Exploitation Index (WEI+) and the reservoirs’ operation with the Reliability index to cover the water demands. The indices of Crop Water Productivity, Nitrogen Use Efficiency, and Economic Water Productivity have been used to quantify the benefits and the feasibility of the alternative scenarios. The best results for the sustainability of water resources are achieved under the deficit irrigation and rain-fed scenario, while the best results for water resources and the local economy are achieved under deficit irrigation and reduced fertilization scenario.

Relative Contribution of the Xiaolangdi Dam to Runoff Changes in the Lower Yellow River

Human activities are increasingly recognized as having a critical influence on hydrological processes under the warming of the climate, particularly for dam-regulated rivers. To ensure the sustainable management of water resources, it is important to evaluate how dam construction may affect surface runoff. In this study, using Mann–Kendall tests, the double mass curve method, and the Budyko-based elasticity method, the effects of climate change and human activities on annual and seasonal runoff were quantified for the Yellow River basin from 1961–2018; additionally, effects on runoff were assessed after the construction of the Xiaolangdi Dam (XLD, started operation in 2001) on the Yellow River. Both annual and seasonal runoff decreased over time (p < 0.01), due to the combined effects of climate change and human activities. Abrupt changes in annual, flood season, and non-flood season runoff occurred in 1986, 1989, and 1986, respectively. However, no abrupt changes were seen after the construction of the XLD. Human activities accounted for much of the reduction in runoff, approximately 75–72% annually, 81–86% for the flood season, and 86–90% for the non-flood season. Climate change approximately accounted for the remainder: 18–25% (annually), 14–19% (flood season), and 10–14% (non-flood season). The XLD construction mitigated runoff increases induced by heightened precipitation and reduced potential evapotranspiration during the post-dam period; the XLD accounted for approximately 52% of the runoff reduction both annually and in the non-flood season, and accounted for approximately −32% of the runoff increase in the flood season. In conclusion, this study provides a basic understanding of how dam construction contributes to runoff changes in the context of climate change; this information will be beneficial for the sustainable management of water resources in regulated rivers.

Grid-Scale Impact of Climate Change and Human Influence on Soil Erosion within East African Highlands (Kagera Basin)

Under global climate change and pressure from human activities, soil erosion is becoming a major concern in the quest for regional sustainable development in the Kagera basin (KB). However, few studies in this region have comprehensively considered the impact of climate change and human influence on soil erosion, and the associated processes are unclear. Based on the premise of quantifying climate change, human influence, and soil erosion, this study undertook a neighborhood analysis as the theoretical support, for a grey relation analysis which was conducted to realize the qualitative assessment of the influence of climate change and human activities on soil erosion. The results show that 90.32% of the KB saw climate change as having a greater influence on soil erosion than human influence, with the remaining area 9.68% seeing human influence having a greater impact than climate change, mainly as a result of the effect of rangeland and farmland. The average soil erosion rate of the KB shows a very low level (10.54 t ha-1 yr-1), with rangeland and farmland being the main land use/land cover (LULC) types that see soil loss, followed by forest, wetland, and built-up areas. The climate change trends of the KB show the most dramatic changes in the northeast and southwest, gradually decreasing towards the line crossing from the Birunga National Park (Rwanda) to the Keza district (Tanzania). The human influence intensity (HII) shows a high level in the KB (21.93), where it is higher in the west and lower in the east of the basin.

Agent-based modelling of water balance in a social-ecological system: A multidisciplinary approach for mountain catchments

The European Alps are known as the 'water towers of Europe'. However, climatic and socioeconomic changes influence both water supply and demand, increasing the need to manage this limited and valuable resource properly to avoid user conflicts and water scarcity. Two major challenges emerge when assessing water scarcity in the Alps: Firstly, mountainous regions are very heterogeneous regarding water availability and demand over space and time, and therefore water scarcity assessments need to be done at low temporal and spatial scales. Secondly, the tight coupling of the natural and the social sphere necessitate an integrative approach considering dynamics and interactions of the social-ecological system. Hence, we applied the agent-based water supply and demand model Aqua.MORE, which is designed for catchment scale and sub-daily temporal resolution, to a case study site in the Italian Alps. In the model, the water supply, the local water managers and water users are represented by interacting model agents. We estimated the water supply by refining the annual runoff data provided by the InVEST water yield model for within-year variations. Local stakeholders contributed to the development of quantitative and spatially-explicit scenarios for land use and tourism evolution. To evaluate water supply and demand dynamics, we assessed six scenarios for the period of 2015 to 2050: three different socio-economic policy pathways, both alone and in combination with a climate change scenario. In all six scenarios, the water demand:supply (D:S) ratio continuously rises from 2015 to 2050.The highest D:S ratio values are prognosed at the beginning of the irrigation period in May. In all scenarios considering climatic changes, the D:S ratio exceeds 20% for several days, indicating potential water scarcity. The simulation results reinforce the importance of analysing water balances at a high temporal resolution and can support management processes and stakeholder dialogues for sustainable watershed management.

Long-term time-scale bonds between discharge regime and catchment specific landscape traits in the Spanish Pyrenees

An analysis of long-term databases with information on precipitation and discharge records was undertaken to characterize the temporal structure response of four experimental catchments, located in the Central Spanish Pyrenees, with a gradient of land-cover (from a relatively pristine forested catchment, through an abandoned cultivated catchment with progressive plant recolonization, to an afforested catchment and ending with a degraded badlands catchment). Precipitation and discharge records are non-stationary and the wavelet transform methodology was thus applied to perform a temporal scale-by-scale analysis of each catchment response to the hydroclimatic characteristics of the area. This temporal decomposition analysis illustrates how land-use and land-cover legacy control the temporal distribution of flow events occurring at different and non-similar time-scales, thus reflecting the timing, variability and physical mechanisms of water storage/transport in each catchment. Intra-annual and annual time-scales are led by climatological characteristics of the catchment sites (seasonal patterns of mountainous Pyrenees catchments). Multi-year scale is mainly shaped by land-cover and land-use legacy. Badlands catchment, with its large proportion of bare land, shows a discharge response closely synchronized with precipitation patterns for all time-scales. On the contrary, for the forested catchment the global hydrological response is mainly governed by the multi-year time-scale. Afforested catchment and abandoned cultivated catchment, which move towards a pristine forest response, are impacted by the former grazing and agriculture activities and intra-annual temporal variability still play a major role on the global discharge response of the catchment. This suggests that vegetated catchments located in the same region can show hydrological responses at different time-scales to the same climatic input. We argue that differences in land-cover and historical land-use changes are not only valuable to understand the current discharge temporal behaviour, but they will also play a significant role in characterizing the future catchment dynamics due to changing climate conditions.

Water and sediment budgets unveiling contrasting hydro-sedimentary patterns in a mountainous Mediterranean catchment

Mountain regions have a key role in the generation of runoff, and in the production and transfer of sediments to fluvial networks, especially in Mediterranean catchments where these processes are affected by marked changes in climate and land use (i.e. global change). This paper presents the water and the sediment budgets of the Ribera Salada (224 km²), a meso-scale Mediterranean forested catchment located in the Southern Pyrenees. Field monitoring follows an integrated basins scheme (five nested sub-catchments), where hydrological and sediment transport data were collected continuously over a two-year period (2012-2013). Precipitation was obtained using radar images, which allowed the elaboration of rainfall maps used to characterize the spatial distribution of rainfall across multiple scales. Results indicate that the catchment is hydrologically divided in two areas which show contrasting fluvial regimes: the upper part of the catchment is considered wet and has a constant flow regime, supplying the majority of the water, while the lower part is drier, with ephemeral tributaries and water losses into the alluvial aquifer of the main river channel. In contrast to water yield, most of the suspended sediment load (i.e. 80%) is supplied by the driest part of the catchment where sediment availability was greater and where there is a greater connectivity between sediment sources and the channel network. The sediment yield of the whole catchment and the respective sub-catchments sits in the lower bounds of values reported for the Mediterranean region, indicating the generally low intensity of hydrological and geomorphic processes in the area. Once more the sediment budget approach matched to sound hydrological data proves efficient to characterize sediment dynamics in river basins, with special interest in areas such as the Mediterranean mountain catchments, where the effects of global change appear to be more acute.

Simulation of streamflow and instream loads of total suspended solids and nitrate in a large transboundary river basin using Source model and geospatial analysis

The management of LULC changes in transboundary river basins continues to challenge water resources managers due to the differences in development and conservation priorities of the countries sharing the basin. While various watershed models (WMs) exist to support decision making, basin-wide sustainable application of the instituted WM depends on the management priorities, resources, data availability, and knowledge gaps at national and sub-basin levels. Building on the results of our prior comparative analysis of WMs for a large transboundary river basin, we applied the 'Source' model to the Lower Mekong Basin (LMB). The constructed LMB-Source model was evaluated based on its streamflow and instream total suspended solids (TSS) and nitrate loads simulative performances. A combination of predictive performance metrics (PPMs) and sophisticated hydrologic signatures were used to calibrate model parameters and diagnose the model performance. Calibration results indicated strong similarity between the simulated and observed time series data and were further confirmed by the validation results. The successful model calibration generated parameters that represent hydrologic response characteristics (HRCs) and overland TSS and nitrate generation and removal dynamics (GRDs) previously not available for the LMB. The HRCs and GRDs can be regionalised with physical attributes of the LMB in future studies which can be used to support the management of ungauged sub-basins. This study confirms Source's capability as a decision support tool for the management of transboundary river basins, and provides basin-specific values of HRCs and GRDs that can be used for a better evaluation of the potential effects of LULC changes.

The Regional Hydro-Ecological Simulation System for 30 Years: A Systematic Review

As the Regional Hydro-Ecological Simulation System (RHESSys) is a tool to simulate the interactions between ecological and hydrological processes, many RHESSys-based studies have been implemented for sustainable watershed management. However, it is crucial to review a RHESSys updating history, pros, and cons for further improving the RHESSys and promoting ecohydrological studies. This paper reviewed the progress of ecohydrological studies employing RHESSys by a bibliometric analysis that quantitatively analyzed the characteristics of relevant studies. In addition, we addressed the main application progress, parameter calibration and validation methods, and uncertainty analysis. We found that since its release in 1993, RHESSys has been widely applied for basins (<100 km2) within mainly seven biomes. The RHESSys model has been applied for evaluating the ecohydrological responses to climate change, land management, urbanization, and disturbances, as well as water quality and biogeochemical cycle. While most studies have paid their attention on climate change, the focus has shifted to the application for land management in recent years. This study also identified many challenges in RHESSys such as the inaccessible data and parameters, oversimplified calibration approach, few applications for large-scale watersheds, and limited application fields. Therefore, this study proposed a set of suggestions to overcome the limitations and challenges: (1) Developing a new approach for parameter acquisition and calibration from multi-source data, (2) improving the applicability for a large-scale basin, and (3) extending the scope of application fields. We believe RHESSys can improve the understandings of human–environment relationships and the promotion of sustainable watersheds development.

Quantifying the impacts of land use/land cover change on the water balance in the afforested River Basin, Pakistan

Land use and land cover (LULC) change is one of the key driving elements responsible for altering the hydrology of a watershed. In this study, we investigated the spatio-temporal LULC changes between 2001 and 2018 and their impacts on the water balance of the Jhelum River Basin. The Soil and Water Assessment Tool (SWAT) was used to analyze the impacts on water yield (WY) and evapotranspiration (ET). The model was calibrated and validated with discharge data between 1995 and 2005 and then simulated with different land use. The increase was observed in forest, settlement and water areas during the study period. At the catchment scale, we found that afforestation has reduced the WY and surface runoff, while enhanced the ET. Moreover, this change was more pronounced at the sub-basin scale. Some sub-basins, especially in the northern part of the study area, exhibited an increase in WY due to an increase in the snow cover area. Similarly, extremes land use scenarios also showed significant impact on water balance components. The basin WY has decreased by 38 mm/year and ET has increased about 36 mm/year. The findings of this study could guide the watershed manager in the development of sustainable LULC planning and water resources management.

Impacts of climate change on reservoir water availability, quality and irrigation needs in a water scarce Mediterranean region (southern Portugal)

Future climate for the Mediterranean climatic region is expected to bring an increase in temperatures, decrease in the precipitation quantity and shifts in the seasonal precipitation pattern. Although the impacts of climate change on water resources have been relatively well explored for the Mediterranean climatic region, the specific consequences for reservoirs and, in particular, water availability and irrigation issues have been less studied. The objective of this work is two-fold: (i) to assess the impacts of future climate changes on water resources availability, quality (focusing on phosphorus loads as this is the limiting nutrient for eutrophication) and irrigation needs for two multipurpose reservoirs in southern Portugal; (ii) to suggest climate change adaptation strategies, especially for the agricultural sector. To this end, the SWAT model was first calibrated against existing data on reservoir inflows as well as phosphorus loads. Then, SWAT was run with climate derived EURO-CORDEX models (RCA4/RACMO22E) for four periods (1970-2000, 2010-2040, 2040-2070 and 2070-2100). Water availability was analysed using the Water Exploitation Index (WEI) that was calculated for both reservoirs combining changes of inflows and irrigation requirements. The results indicated that climate change will negatively impact water availability in both reservoirs, especially under RCP8.5. In the case of the Monte Novo reservoir, future domestic water supply could be constrained by water quality problems related with phosphorus loads. For Vigia reservoir, the high water exploitation will lead to water scarcity problems, mainly as this reservoir on present-day conditions is restrictive on irrigation requirements. Adaptation strategies such as the implementation of high end technology (e.g. soil moisture and plant water stress probes, satellite imagery and drones to evaluate water stress - NDVI) as well as the renewal of the irrigation network and adequate crop selection can help attenuating the effects of climate change on the water resources in this region.

Environmental Scenario Analysis on Natural and Social-Ecological Systems: A Review of Methods, Approaches and Applications

Scenario analysis is a useful tool to facilitate discussions about the main trends of future change and to promote the understanding of global environmental changes implications on relevant aspects of sustainability. In this paper, we reviewed 294 articles published between 1995–2019, to evaluate the state of the art use of models and scenarios to investigate the effects of land use change and climate change on natural and social-ecological systems. Our review focuses on three issues. The first explores the extent to which the environmental dynamics of land use and climate change were jointly analyzed and the spatial scales associated with such integrated studies. The second explores the modelling methodologies and approaches used in the scenario analysis. The third explores the methods for developing or building scenarios. Results show that in most predictions there is little integration of key drivers of change. We find most forecasting studies use a sectoral modelling approach through dynamic spatially distributed models. Most articles do not apply a participatory approach in the development of scenarios. Based on this review, we conclude that there are some gaps in how scenario analysis on natural and social-ecological systems are conducted. These gaps pose a challenge for the use of models and scenarios as predictive tools in decision-making processes in the context of global change.

Effects of active and passive land use management after cropland abandonment on water and vegetation dynamics in the Central Spanish Pyrenees

The Mediterranean mountains have been subject to significant land abandonment process during the second half of the 20th century. The subsequent natural revegetation following abandonment in rural areas has been widely documented to have substantial implications on the hydrological cycle and the vegetation. The Spanish Pyrenees are one of the most affected areas by these land transformations which could threaten their importance for water supply and agricultural activities in the downstream lowland areas. Land managers as well as scientists around the world have taken different positions on how to deal with these land use changes. Some are in favor of active management (AM) (i.e. density reduction) while others are supporting passive management (PM) (letting the process of revegetation continue). This study aims to investigate the implication of AM and PM on hydrological and vegetation dynamics under different climate trajectories in a representative abandoned cropland catchment in the Central Spanish Pyrenees. A coupled ecohydrologic model is used to estimate the post management response of streamflow (STR), evapotranspiration (ET), soil saturation deficit (SD) and plant carbon (PC) following shrub clearing. Clearing increased annual STR by 16%, while ET and SD decreased by around -9% and -6% respectively during the first year after management with changes to monthly flows. These changes to water regimes may be even higher in wetter years. Over a 10-years period of vegetation recovery annual STR increased between 7.1% and 24.2%, while annual ET and SD decreased between -2.6% to -8.7% and -2.7% to -6% respectively due to shrub clearing, with the highest changes occurring in the first three years of AM. On the effect of climate change, our results show that a 2 °C increase in temperature could reduce AM effects on water regimes and accelerate the recovery of PC given averaged rainfall conditions.

A Forty-Year Karstic Critical Zone Survey (Baget Catchment, Pyrenees-France): Lithologic and Hydroclimatic Controls on Seasonal and Inter-Annual Variations of Stream Water Chemical Composition, pCO2, and Carbonate Equilibrium

The long-term trends and seasonal patterns of stream water chemical composition in a small remote forested karst catchment, were investigated from 1978 to 2018. Calcium, magnesium, and bicarbonates, the dominant ions, increased over the period together with temperature, while sulfates decreased. Carbonate and sulfate mineral dissolution was the main source of these elements. These trends and the seasonal opposite patterns of discharge vs. temperature, calcite saturation index vs. pCO2 and bicarbonate vs. sulfates, suggested the influence of discharge, of reduced long-range atmospheric pollution, and of increasing air temperature on biological activity and carbonate dissolution. Furthermore, the hydrological regime controlled the seasonal stream water chemical composition and fluxes by: (i) a dilution during the high discharge period, (ii) a change in the contribution rate of the waters draining different lithological areas in the catchment, e.g., the increased sulfates to bicarbonates ratio during summer low flows, with a maximum alkalinity decrease of 24%, and (iii) a “piston” and a “flushing” effects of dissolved elements stored in soils and epikarst with the first autumn heavy rains. Long-term stream water hydrochemical surveys of karst system have proved to be powerful indicators of biogeochemical processes, water sources and pathways under variable natural and anthropogenic environmental pressure conditions.

Impacts of Climate and Land-Use Changes on the Hydrological Processes in the Amur River Basin

Under the joint effects resulted from different changes of climate and land-use regimes, spatial-temporal variations of hydrological processes took place in certain principles. Identifying the impact of changes in individual land-use types/climatic factors on hydrological processes is significant for water management and sustainability of watersheds. In this study, seven simulation scenarios were developed using the soil and water assessment tool (SWAT) model to distinguish the impacts of climate and land-use changes on the hydrological processes in the Amur River Basin (ARB) for four periods of 1980–1990, 1991–1999, 2000–2006, and 2007–2013, respectively. Based on the multi-period simulation scenario data, partial least squares regression and ridge regression analyses were performed to further evaluate the effects of changes in individual land-use types/climatic factors on hydrologic components. The results suggested that summer precipitation and summer average temperature were the dominant climatic factors, and crops and wetlands were the principal land-use types contributing to the hydrological responses. In addition, the drastic changes in crop and wetland areas and a clear decline in summer precipitation between the periods of 1991–1999 and 2000–2006 may account for the highest-intensity impacts of climate and land-use changes on the runoff at the outlet (−31.38% and 16.17%, respectively) during the four periods.

Mechanistic simulations predict that thermal and hydrological effects of climate change on Mediterranean trout cannot be offset by adaptive behaviour, evolution, and increased food production

Streamflow is a main driver of fish population dynamics and is projected to decrease in much of the northern hemisphere, especially in the Mediterranean region, due to climate change. However, predictions of future climate effects on cold-water freshwater fish populations have typically focused only on the ecological consequences of increasing temperatures, overlooking the concurrent and interacting effects of climate-driven changes in streamflow regimes. Here, we present simulations that contrasted the consequences of changes in thermal regime alone versus the combined effects of changes in thermal regime and streamflow for resident trout populations in distinct river types with different sensitivities to climatic change (low-altitude main river vs. high-altitude headwaters). We additionally assessed the buffering effect of increased food production that may be linked to warming. We used an eco-genetic individual-based model that integrates the behavioural and physiological effects of extrinsic environmental drivers -temperature and flow- with intrinsic dynamics -density-dependence, phenotypic plasticity and evolutionary responses - across the entire trout life cycle, with Mediterranean brown trout Salmo trutta as the model species. Our simulations indicated that: (1) Hydrological change is a critical dimension of climate change for the persistence of trout populations, in that neither river type supported viable populations under strong rates of flow change, even under scenarios of increased food production. (2) Climate-change-related environmental change most affects the largest, oldest trout via increased metabolic costs and decreased energy inputs. In both river types, populations persisted under extreme warming alone but became dominated by younger, smaller fish. (3) Density-dependent, plastic and evolutionary changes in phenology and life-history traits provide trout populations with important resilience to warming, but strong concurrent shifts in streamflow could exceed the buffering conferred by such intrinsic dynamics.

Evaluating Water Resource Accessibility in Southwest China

The accessibility, quantity, and quality of water resources are the basic requirements for guaranteeing water resource security. Research into regional water resource accessibility will contribute to improving regional water resource security and effective water resource management. In this study, we used a water resource accessibility index model considering five spatial factors to evaluate the grid-scale water resource accessibility and constructed the spatial pattern of water resource accessibility in Southwest China. Then, we analyzed the coupling coordination degree between county-level water resource accessibility and eco-socio-economic water demand elements. The water resource accessibility showed obvious regional differences, and the overall trend gradually decreased from Southeast to Northwest. The coupling coordination degree between county-level water resource accessibility and eco-socio-economic water demand elements was between 0.26 and 0.84, and was relatively low overall, whereas the counties (districts) with high coordination, moderate coordination, low coordination, reluctant coordination, and incoordination accounted for 0.92%, 5.31%, 21.06%, 59.71%, and 13.00% of total counties (districts), respectively. Therefore, the Southwest region needs to further strengthen the construction of its agricultural irrigation facilities, protect the water resources, and coordinate the relationship between water resource management and water demand elements to comprehensively guarantee regional sustainable development.

Runoff and Solute Outputs under Different Land Uses: Long-Term Results from a Mediterranean Mountain Experimental Station

Water availability and quality in Mediterranean environments are largely related to the spatial organisation of land uses in mountain areas, where most water resources are generated. However, there is scant data available on the potential effects of land use changes on surface water chemistry in the Mediterranean mountain region. In order to address this gap in the research, this study investigates the effects of various mountain Mediterranean land covers/land uses on runoff water yielded and water chemistry (solute concentrations and loads) using data from the Aísa Valley Experimental Station (Central Pyrenees) for a long-term period (1991–2011). Nine land covers have been reproduced in closed plots, including dense shrub cover, grazing meadows, cereal, fallow land, abandoned field, shifting agriculture (active and abandoned) and 2 burned plots (one burned in 1991 and the second one burned twice in 1993 and 2001). Results show that all solute concentrations differed among land uses, with agricultural activity producing significantly higher solute loads and concentrations than the other types. Two groups have been identified: (i) the lowest solute concentrations and the smallest quantities of solute loads are recorded in the dense shrub cover, the plot burned once (at present well colonized with shrubs), meadows and abandoned field plots; (ii) the plot burned twice registered moderate values and the highest solute concentrations and loads are found in cereal, fallow land and shifting agriculture plots. Water chemistry is clearly dominated by Ca2+ and HCO3− concentrations, whereas other solutes are exported in very low quantities due to the poor nutrient content of the soil. These results complete the information published previously on soil erosion under different land uses in this experimental station and help to explain the evolution of land cover as a consequence of shifting agriculture, cereal farming on steep slopes and the use of recurrent fires to favour seasonal grazing. They also suggest that promoting the development of grazing and cutting meadows is a good strategy to reduce not only soil erosion but also the loss of nutrients.

Sensitivity of Potential Groundwater Recharge to Projected Climate Change Scenarios: A Site-Specific Study in the Nebraska Sand Hills, USA

Assessing the relationship between climate forcings and groundwater recharge (GR) rates in semi-arid regions is critical for water resources management. This study presents the impact of climate forecasts on GR within a probabilistic framework in a site-specific study in the Nebraska Sand Hills (NSH), the largest stabilized sand dune region in the USA containing the greatest recharge rates within the High Plains Aquifer. A total of 19 downscaled climate projections were used to evaluate the impact of precipitation and reference evapotranspiration on GR rates simulated by using HYDRUS 1-D. The analysis of the decadal aridity index (AI) indicates that climate class will likely remain similar to the historic average in the RCP2.6, 4.5, and 6.0 emission scenarios but AI will likely decrease significantly under the worst-case emission scenario (RCP8.5). However, GR rates will likely decrease in all of the four emission scenarios. The results show that GR generally decreases by ~25% under the business-as-usual scenario and by nearly 50% in the worst-case scenario. Moreover, the most likely GR values are presented with respect to probabilities in AI and the relationship between annual-average precipitation and GR rate were developed in both historic and projected scenarios. Finally, to present results at sub-annual time resolution, three representative climate projections (dry, mean and wet scenarios) were selected from the statistical distribution of cumulative GR. In the dry scenario, the excessive evapotranspiration demand in the spring and precipitation deficit in the summer can cause the occurrence of wilting points and plant withering due to excessive root-water-stress. This may pose significant threats to the survival of the native grassland ecology in the NSH and potentially lead to desertification processes if climate change is not properly addressed.

Effects of land use and spatial processes in water and surface sediment of tropical reservoirs at local and regional scales

The effects of land use and connectivity on the characteristics of aquatic ecosystems are thought to be scale-dependent. This study aimed to evaluate the relationships between land use and reservoir characteristics at two spatial scales, after controlling for spatial processes. Water and surface sediment samples were collected from 31 sites (7 reservoirs) in the Paiva Castro and Piracicaba River basins (Cantareira System, São Paulo State, Brazil), during austral summer and winter. The dataset included 15 water quality variables and 6 surface sediment variables. Land use variables (natural areas, pasture, agriculture and urban areas) were obtained at two spatial scales (buffer and watershed) in each reservoir. Spatial variables were calculated using Moran's Eigenvectors Maps and Asymmetric Eigenvector Maps. The strengths of the relationships between land use and sediment variables were stronger than those between land use and water quality variables. The strengths of some of the relationships were scale-dependent. Finally, spatial processes, mostly hydrological connectivity, play an important role in water-sediment quality and should be considered in landscape management programs.

The Influence of Climate and Land-Cover Scenarios on Dam Management Strategies in a High Water Pressure Catchment in Northeast Spain

This paper evaluates the response of streamflow in a Mediterranean medium-scaled basin under land-use and climate change scenarios and its plausible implication on the management of Boadella–Darnius reservoir (NE Spain). Land cover and climate change scenarios supposed over the next several decades were used to simulate reservoir inflow using the Regional Hydro-Ecologic Simulation System (RHESsys) and to analyze the future impacts on water management (2021–2050). Results reveal a clear decrease in dam inflow (−34%) since the dam was operational from 1971 to 2013. The simulations obtained with RHESsys show a similar decrease (−31%) from 2021 to 2050. Considering the ecological minimum flow outlined by water authorities and the projected decrease in reservoir’s inflows, different water management strategies are needed to mitigate the effects of the expected climate change.

Combination of lumped hydrological and remote-sensing models to evaluate water resources in a semi-arid high altitude ungauged watershed of Sierra Nevada (Southern Spain)

Assessing water resources in high mountain semi-arid zones is essential to be able to manage and plan the use of these resources downstream where they are used. However, it is not easy to manage an unknown resource, a situation that is common in the vast majority of high mountain hydrological basins. In the present work, the discharge flow in an ungauged basin is estimated using the hydrological parameters of an HBV (Hydrologiska Byråns Vattenbalansavdelning) model calibrated in a "neighboring gauged basin". The results of the hydrological simulation obtained in terms of average annual discharge are validated using the VI-ETo model. This model relates a simple hydrological balance to the discharge of the basin with the evaporation of the vegetal cover of the soil, and this to the SAVI index, which is obtained remotely by means of satellite images. The results of the modeling for both basins underscore the role of the underground discharge in the total discharge of the hydrological system. This is the result of the deglaciation process suffered by the high mountain areas of the Mediterranean arc. This process increases the infiltration capacity of the terrain, the recharge and therefore the discharge of the aquifers that make up the glacial and periglacial sediments that remain exposed on the surface as witnesses of what was the last glaciation.

Groundwater discharge in high-mountain watersheds: A valuable resource for downstream semi-arid zones. The case of the Bérchules River in Sierra Nevada (Southern Spain)

Aquifers in permeable formations developed in high-mountain watersheds slow down the transfer of snowmelt to rivers, modifying rivers' flow pattern. To gain insight into the processes that control the hydrologic response of such systems the role played by groundwater in an alpine basin located at the southeastern part of the Iberian Peninsula is investigated. As data in these environments is generally scarce and its variability is high, simple lumped parameter hydrological models that consider the groundwater component and snow accumulation and melting are needed. Instead of using existing models that use many parameters, the Témez lumped hydrological model of common use in Spain and Ibero-American countries is selected and modified to consider snow to get a simplified tool to separate hydrograph components. The result is the TDD model (Témez-Degree Day) which is applied in a high mountain watershed with seasonal snow cover in Southern Spain to help in quantifying groundwater recharge and determining the groundwater contribution to the outflow. Average groundwater recharge is about 23% of the precipitation, and groundwater contribution to total outflow ranges between 70 and 97%. Direct surface runoff is 1% of precipitation. These values depend on the existence of snow. Results are consistent with those obtained with chloride atmospheric deposition mass balances by other authors. They highlight the important role of groundwater in high mountain areas, which is enhanced by seasonal snow cover. Results compare well with other areas. This effect is often neglected in water planning, but can be easily taken into account just by extending the water balance tool in use, or any other, following the procedure that has being developed.

Combined impacts of climate and socio-economic scenarios on irrigation water availability for a dry Mediterranean reservoir

The impacts of climate and associated socio-economic changes on water availability, including supply and demand, quality, and storage volume, were evaluated for the Vale do Gaio reservoir in southern Portugal, located in a dry Mediterranean climate and already under drought stress. The SWAT model was applied with 6 scenarios for 2071-2100, involving two storylines (A1B and B1) with individual changes in climate (-9% rainfall, increasing in winter by +28 to +30%), socio-economic conditions (an increase in irrigation demand by 11%, and a replacement of cereals and pastures by sunflower), and a combination of both. Most future scenarios resulted in lower water availability, due to lower supply (-19 to -27%) combined with higher irrigation demand (+3 to +21%). This resulted in more years with limited irrigation supplies (presently: 28%; scenarios: 37 to 43%), although limitations were mitigated by lower losses to excess discharge. Land-use changes also decreased quality by increasing P concentrations (+29 to +93%). Impacts were more severe in scenario A1B than in B1, and in combined changes than in climate or socio-economic changes only. Water availability was resilient to climate change, as impacts led only to a moderate aggravation of present-day conditions. Lower future water availability could be addressed by supply and demand management strategies and, in the most extreme scenario, by water transfers from regional water reserves; water quality issues could be addressed through land-use policies. Results also highlighted the importance of taking the characteristics of water supply systems into account when designing adaptation measures for future changes.

Farmland-atmosphere feedbacks amplify decreases in diffuse nitrogen pollution in a freeze-thaw agricultural area under climate warming conditions

Although climate warming and agricultural land use changes are two of the primary instigators of increased diffuse pollution, they are usually considered separately or additively. This likely lead to poor decisions regarding climate adaptation. Climate warming and farmland responses have synergistic consequences for diffuse nitrogen pollution, which are hypothesized to present different spatio-temporal patterns. In this study, we propose a modeling framework to simulate the synergistic impacts of climate warming and warming-induced farmland shifts on diffuse pollution. Active accumulated temperature response for latitudinal and altitudinal directions was predicted based on a simple agro-climate model under different temperature increments (△T₀ is from 0.8°C to 1.4°C at an interval of 0.2°C). Spatial distributions of dryland shift to paddy land were determined by considering accumulated temperature. Different temperature increments and crop distributions were inserted into Soil and Water Assessment Tool model, which quantified the spatio-temporal changes of nitrogen. Warming led to a decrease of the annual total nitrogen loading (2.6%-14.2%) in the low latitudes compared with baseline, which was larger than the decrease (0.8%-6.2%) in the high latitudes. The synergistic impacts amplified the decrease of the loading in the low and high latitudes at the sub-basin scale. Warming led to a decrease of the loading at a rate of 0.35kg/ha/°C, which was lower than the synergistic impacts (3.67kg/ha/°C) at the watershed level. However, warming led to the slight increase of the annual averaged NO3 (LAT) (0.16kg/ha/°C), which was amplified by the synergistic impacts (0.22kg/ha/°C). Expansion of paddy fields led to a decrease in the monthly total nitrogen loading throughout the year, but amplified an increase in the loading in August and September. The decreased response in spatio-temporal nitrogen patterns is substantially amplified by farmland-atmosphere feedbacks associated with farmland shifts in response to warming.

Determining the hydrological responses to climate variability and land use/cover change in the Loess Plateau with the Budyko framework

Understanding and quantifying the impacts of land use/cover change and climate variability on hydrological responses are important to the design of water resources and land use management strategies for adaptation to climate change, especially in water-limited areas. The elasticity method was used to detect the responses of streamflow and runoff coefficient to various driving factors in 15 main catchments of the Loess Plateau, China between 1961 and 2009. The elasticity of streamflow (Q) and runoff coefficient (Rc) to precipitation (P), potential evapotranspiration (E0), and catchment characteristics (represented by the parameter m in Fu's equation) were derived based on the Budyko hypothesis. There were two critical values of m=2 and E0/P=1 for the elasticity of Q and Rc. The hydrological responses were mainly affected by catchment characteristics in water-limited regions (E0/P>1), and in humid areas (E0/P<1), climate conditions played a more important role for cases of m>2 whereas catchment characteristics had a greater impact for cases of m<2. The annual Q and Rc in 14 of the 15 catchments significantly decreased with average reduction of 0.87mmyr(-1) and 0.18%yr(-1), respectively. The mean elasticities of Q to P, E0 and m were 2.66, -1.66 and -3.17, respectively. The contributions of land use/cover change and P reduction to decreased Q were 64.75% and 41.55%, respectively, while those to decreased Rc were 75.68% and 32.06%, respectively. In contrast, the decreased E0 resulted in 6.30% and 7.73% increase of Q and Rc, respectively. The contribution of land use/cover changes was significantly and positively correlated with the increase in the percentage of the soil and water conservation measures area (p<0.05). The Rc significantly and linearly decreased with the vegetation coverage (p<0.01). Moreover, the Rc linearly decreased with the percentage of measures area in all catchments (eight of them were statistically significant with p<0.05).

Impacts of future climate change on river discharge based on hydrological inference: A case study of the Grand River Watershed in Ontario, Canada

Over the recent years, climate change impacts have been increasingly studied at the watershed scale. However, the impact assessment is strongly dependent upon the performance of the climatic and hydrological models. This study developed a two-step method to assess climate change impacts on water resources based on the Providing Regional Climates for Impacts Studies (PRECIS) modeling system and a Hydrological Inference Model (HIM). PRECIS runs provided future temperature and precipitation projections for the watershed under the Intergovernmental Panel on Climate Change SRES A2 and B2 emission scenarios. The HIM based on stepwise cluster analysis is developed to imitate the complex nonlinear relationships between climate input variables and targeted hydrological variables. Its robust mathematical structure and flexibility in predictor selection makes it a desirable tool for fully utilizing various climate modeling outputs. Although PRECIS and HIM cannot fully cover the uncertainties in hydro-climate modeling, they could provide efficient decision support for investigating the impacts of climate change on water resources. The proposed method is applied to the Grand River Watershed in Ontario, Canada. The model performance is demonstrated with comparison to observation data from the watershed during the period 1972-2006. Future river discharge intervals that accommodate uncertainties in hydro-climatic modeling are presented and future river discharge variations are analyzed. The results indicate that even though the total annual precipitation would not change significantly in the future, the inter-annual distribution is very likely to be altered. The water availability is expected to increase in Winter while it is very likely to decrease in Summer over the Grand River Watershed, and adaptation strategies would be necessary.

Impacts of climate change on precipitation and discharge extremes through the use of statistical downscaling approaches in a Mediterranean basin

Mediterranean region is characterized by high precipitation variability often enhanced by orography, with strong seasonality and large inter-annual fluctuations, and by high heterogeneity of terrain and land surface properties. As a consequence, catchments in this area are often prone to the occurrence of hydrometeorological extremes, including storms, floods and flash-floods. A number of climate studies focused in the Mediterranean region predict that extreme events will occur with higher intensity and frequency, thus requiring further analyses to assess their effect at the land surface, particularly in small- and medium-sized watersheds. In this study, climate and hydrologic simulations produced within the Climate Induced Changes on the Hydrology of Mediterranean Basins (CLIMB) EU FP7 research project were used to analyze how precipitation extremes propagate into discharge extremes in the Rio Mannu basin (472.5km(2)), located in Sardinia, Italy. The basin hydrologic response to climate forcings in a reference (1971-2000) and a future (2041-2070) period was simulated through the combined use of a set of global and regional climate models, statistical downscaling techniques, and a process based distributed hydrologic model. We analyzed and compared the distribution of annual maxima extracted from hourly and daily precipitation and peak discharge time series, simulated by the hydrologic model under climate forcing. For this aim, yearly maxima were fit by the Generalized Extreme Value (GEV) distribution using a regional approach. Next, we discussed commonality and contrasting behaviors of precipitation and discharge maxima distributions to better understand how hydrological transformations impact propagation of extremes. Finally, we show how rainfall statistical downscaling algorithms produce more reliable forcings for hydrological models than coarse climate model outputs.

Potential impacts of climate change on flow regime and fish habitat in mountain rivers of the south-western Balkans

The climate change in the Mediterranean area is expected to have significant impacts on the aquatic ecosystems and particular in the mountain rivers and streams that often host important species such as the Salmo farioides, Karaman 1938. These impacts will most possibly affect the habitat availability for various aquatic species resulting to an essential alteration of the water requirements, either for dams or other water abstractions, in order to maintain the essential levels of ecological flow for the rivers. The main scope of this study was to assess potential climate change impacts on the hydrological patterns and typical biota for a south-western Balkan mountain river, the Acheloos. The altered flow regimes under different emission scenarios of the Intergovernmental Panel on Climate Change (IPCC) were estimated using a hydrological model and based on regional climate simulations over the study area. The Indicators of Hydrologic Alteration (IHA) methodology was then used to assess the potential streamflow alterations in the studied river due to predicted climate change conditions. A fish habitat simulation method integrating univariate habitat suitability curves and hydraulic modeling techniques were used to assess the impacts on the relationships between the aquatic biota and hydrological status utilizing a sentinel species, the West Balkan trout. The most prominent effects of the climate change scenarios depict severe flow reductions that are likely to occur especially during the summer flows, changing the duration and depressing the magnitude of the natural low flow conditions. Weighted Usable Area-flow curves indicated the limitation of suitable habitat for the native trout. Finally, this preliminary application highlighted the potential of science-based hydrological and habitat simulation approaches that are relevant to both biological quality elements (fish) and current EU Water policy to serve as efficient tools for the estimation of possible climate change impacts on the south-western Balkan river ecosystems.

Dynamic integration of land use changes in a hydrologic assessment of a rapidly developing Indian catchment

Rapid land use and land-cover changes strongly affect water resources. Particularly in regions that experience seasonal water scarcity, land use scenario assessments provide a valuable basis for the evaluation of possible future water shortages. The objective of this study is to dynamically integrate land use model projections with a hydrologic model to analyze potential future impacts of land use change on the water resources of a rapidly developing catchment upstream of Pune, India. For the first time projections from the urban growth and land use change model SLEUTH are employed as a dynamic input to the hydrologic model SWAT. By this means, impacts of land use changes on the water balance components are assessed for the near future (2009-2028) employing four different climate conditions (baseline, IPCC A1B, dry, wet). The land use change modeling results in an increase of urban area by +23.1% at the fringes of Pune and by +12.2% in the upper catchment, whereas agricultural land (-14.0% and -0.3%, respectively) and semi-natural area (-9.1% and -11.9%, respectively) decrease between 2009 and 2028. Under baseline climate conditions, these land use changes induce seasonal changes in the water balance components. Water yield particularly increases at the onset of monsoon (up to +11.0mm per month) due to increased impervious area, whereas evapotranspiration decreases in the dry season (up to -15.1mm per month) as a result of the loss of irrigated agricultural area. As the projections are made for the near future (2009-2028) land use change impacts are similar under IPCC A1B climate conditions. Only if more extreme dry years occur, an exacerbation of the land use change impacts can be expected. Particularly in rapidly changing environments an implementation of both dynamic land use change and climate change seems favorable to assess seasonal and gradual changes in the water balance.

Impacts of climate and land use changes on the hydrological and erosion processes of two contrasting Mediterranean catchments

The impacts of climate and land use changes on streamflow and sediment export were evaluated for a humid (São Lourenço) and a dry (Guadalupe) Mediterranean catchment, using the SWAT model. SWAT was able to produce viable streamflow and sediment export simulations for both catchments, which provided a baseline for investigating climate and land use changes under the A1B and B1 emission scenarios for 2071-2100. Compared to the baseline scenario (1971-2000), climate change scenarios showed a decrease in annual rainfall for both catchments (humid: -12%; dry: -8%), together with strong increases in rainfall during winter. Land use changes were derived from a socio-economic storyline in which traditional agriculture is replaced by more profitable land uses (i.e. corn and commercial forestry at the humid site; sunflower at the dry site). Climate change projections showed a decrease in streamflow for both catchments, whereas sediment export decreased only for the São Lourenço catchment. Land use changes resulted in an increase in streamflow, but the erosive response differed between catchments. The combination of climate and land use change scenarios led to a reduction in streamflow for both catchments, suggesting a domain of the climatic response. As for sediments, contrasting results were observed for the humid (A1B: -29%; B1: -22%) and dry catchment (A1B: +222%; B1: +5%), which is mainly due to differences in the present-day and forecasted vegetation types. The results highlight the importance of climate-induced land-use change impacts, which could be similar to or more severe than the direct impacts of climate change alone.

Climatic and anthropogenic changes in Western Switzerland: Impacts on water stress

Recent observed hydro-climatic changes in mountainous areas are of concern as they may directly affect capacity to fulfill water needs. The canton of Vaud in Western Switzerland is an example of such a region as it has experienced water shortage episodes during the past decade. Based on an integrated modeling framework, this study explores how hydro-climatic conditions and water needs could evolve in mountain environments and assesses their potential impacts on water stress by the 2060 horizon. Flows were simulated based on a daily semi-distributed hydrological model. Future changes were derived from Swiss climate scenarios based on two regional climate models. Regarding water needs, the authorities of the canton of Vaud provided a population growth scenario while irrigation and livestock trends followed a business-as-usual scenario. Currently, the canton of Vaud experiences moderate water stress from June to August, except in its Alpine area where no stress is noted. In the 2060 horizon, water needs could exceed 80% of the rivers' available resources in low- to mid-altitude environments in mid-summer. This arises from the combination of drier and warmer climate that leads to longer and more severe low flows, and increasing urban (+40%) and irrigation (+25%) water needs. Highlighting regional differences supports the development of sustainable development pathways to reduce water tensions. Based on a quantitative assessment, this study also calls for broader impact studies including water quality issues.

Evaluating options for balancing the water-electricity nexus in California: Part 2--greenhouse gas and renewable energy utilization impacts

A study was conducted to compare the technical potential and effectiveness of different water supply options for securing water availability in a large-scale, interconnected water supply system under historical and climate-change augmented inflow and demand conditions. Part 2 of the study focused on determining the greenhouse gas and renewable energy utilization impacts of different pathways to stabilize major surface reservoir levels. Using a detailed electric grid model and taking into account impacts on the operation of the water supply infrastructure, the greenhouse gas emissions and effect on overall grid renewable penetration level was calculated for each water supply option portfolio that successfully secured water availability from Part 1. The effects on the energy signature of water supply infrastructure were found to be just as important as that of the fundamental processes for each option. Under historical (baseline) conditions, many option portfolios were capable of securing surface reservoir levels with a net neutral or negative effect on emissions and a benefit for renewable energy utilization. Under climate change augmented conditions, however, careful selection of the water supply option portfolio was required to prevent imposing major emissions increases for the system. Overall, this analysis provided quantitative insight into the tradeoffs associated with choosing different pathways for securing California's water supply.

Assessing the impacts of climatic change on mountain water resources

As the evidence for human induced climate change becomes clearer, so too does the realization that its effects will have impacts on numerous environmental and socio-economic systems. Mountains are recognized as very sensitive physical environments with populations whose histories and current social positions often strain their capacity to accommodate intense and rapid changes to their resource base. It is thus essential to assess the impacts of a changing climate, focusing on the quantity of water originating in mountain regions, particularly where snow and ice melt represent a large streamflow component as well as a local resource in terms of freshwater supply, hydropower generation, or irrigation. Increasing evidence of glacier retreat, permafrost degradation and reduced mountain snowpack has been observed in many regions, thereby suggesting that climate change may seriously affect streamflow regimes. These changes could in turn threaten the availability of water resources for many environmental and economic systems, and exacerbate a range of natural hazards that would compound these impacts. As a consequence, socio-economic structures of downstream living populations would be also impacted, calling for better preparedness and strategies to avoid conflicts of interest between water-dependent economic actors. This paper is thus an introduction to the Special Issue of this journal dedicated to the European Union Seventh Framework Program (EU-FP7) project ACQWA (Assessing Climate Impacts on the Quantity and Quality of WAter), a major European network of scientists that was coordinated by the University of Geneva from 2008 to 2014. The goal of ACQWA has been to address a number of these issues and propose a range of solutions for adaptation to change and to help improve water governance in regions where quantity, seasonality, and perhaps quality of water may substantially change in coming decades.