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One of the most important interactions between humans and climate is in the demand and supply of water. Humans withdraw, use, and consume water and return waste water to the environment for a variety of socioeconomic purposes, including domestic, commercial, and industrial use, production of energy resources and cooling thermal-electric power plants, and growing food, fiber, and chemical feed stocks for human consumption. Uncertainties in the future human demand for water interact with future impacts of climatic change on water supplies to impinge on water management decisions at the international, national, regional, and local level, but until recently tools were not available to assess the uncertainties surrounding these decisions. This paper demonstrates the use of a multi-model framework in a structured sensitivity analysis to project and quantify the sensitivity of future deficits in surface water in the context of climate and socioeconomic change for all U.S. states and sub-basins. The framework treats all sources of water demand and supply consistently from the world to local level. The paper illustrates the capabilities of the framework with sample results for a river sub-basin in the U.S. state of Georgia. [ABSTRACT FROM AUTHOR]

Water allocation institutions globally must operate within legal and political contexts established by precedent and codified in operating rules, even as they flex and adjust to climate change. California's Central Valley Water System (CVS) is a prime example. Recent global, national, regional, and local climate change assessments have highlighted climate-change-driven impacts on the CVS; however, these previous studies have not discussed the relative likelihood of performance decline, making it difficult to use the information for planning. In response, this paper presents a systematic climate change stress test that utilizes a physically based hydrologic model linked with a water resources system model representing the infrastructure, operations, and policy constraints of the interconnected system of natural river channels and man-made facilities that comprise the CVS. The results provide a summary of the sensitivity of the system to climate change, indicating the specific climate changes that cause performance of the system to decline below historical norms, and an estimation of the General Circulation Model (GCM) informed probability of those changes by 2050. Degraded performance is especially likely for State Water Project (SWP) deliveries (> 85%), and September carryover/drought storage in the Oroville Reservoir (the SWP's largest reservoir, ~ 95% likely to degrade). A decline in Net Delta Outflow is likely in all seasons except summer and early fall (when regulations require supplemental releases to combat salinity from sea level rise). For most of these metrics, the modeled performance drop is more severe in dry years than in wet years. [ABSTRACT FROM AUTHOR]

Semi-arid regions are known for erratic precipitation patterns with significant effects on the hydrological cycle and water resources availability. High temporal and spatial variation in precipitation causes large variability in runoff over short durations. Due to low soil water storage capacity, base flow is often missing and rivers fall dry for long periods. Because of its climatic characteristics, the semi-arid north-eastern region of Brazil is prone to droughts. To counter these, reservoirs were built to ensure water supply during dry months. This paper describes problems and solutions when calibrating and validating the eco-hydrological model SWIM for semi-arid regions on the example of the Pajeú watershed in north-eastern Brazil. The model was calibrated to river discharge data before the year 1983, with no or little effects of water management, applying a simple and an enhanced approach. Uncertainties result mainly from the meteorological data and observed river discharges. After model calibration water management was included in the simulations. Observed and simulated reservoir volumes and river discharges are compared. The calibrated and validated models were used to simulate the impacts of climate change on hydrological processes and water resources management using data of two representative concentration pathways (RCP) and five earth system models (ESM). The differences in changes in natural and managed mean discharges are negligible (< 5%) under RCP8.5 but notable (> 5%) under RCP2.6 for the ESM ensemble mean. In semi-arid catchments, the enhanced approach should be preferred, because in addition to discharge, a second variable, here evapotranspiration, is considered for model validation. [ABSTRACT FROM AUTHOR]

Hydrologists are commonly involved in impact, adaption and vulnerability assessments for climate change projections. This paper presents a framework for how such assessments can better differentiate between the impacts of climate change and those of natural variability, an important differentiation as it relates to the vulnerability to water availability under change. The key concept involved is to characterize "hydrologic stress" relative to the range of behaviour encountered under baseline conditions, where the degree to which climate change causes the behaviour of a system to shift outside this baseline range provides a non-dimensional measure of stress. The concept is applicable to any system that is subject to climate forcings, though the approach is applied here to a range of examples illustrative of many environmental and engineering applications. These include hydrologic systems that are dependent on the frequency of flows above or below selected thresholds, those that are dominated by storage and those which are sensitive to the sequencing of selected flow components. The analyses illustrate that systems designed or adapted to accommodate high variability are less stressed by a given magnitude of climate impacts than those operating under more uniform conditions. The metrics characterize hydrologic stress in a manner that can facilitate comparison across different regions, or across different assets within a region. Adoption of the approach requires reliance on the use of climate ensembles that represent aleatory uncertainty under both baseline and impacted conditions, and this has implications for how the outputs of climate models are provided and utilized. [ABSTRACT FROM AUTHOR]

This paper applies an ontological politics approach for studying how complexity, uncertainty, and ignorance are being dealt with in the Netherlands by looking at how knowledges are produced and incorporated in decision-making on uncertain climate change. On the basis of work done in the Netherlands, this paper shows two things in particular. First, how decision making responses historically have been subject to change under the influence of floods and how the emergence of climate change has significantly changed these floods. Second, based on the analysis of processes dealing with a blue-green algae problem in a lake, climate change not only changed decision making responses but also changed the very reality that is being enacted. Consequently, this brings an ethical dimension to the fore, related to the intrinsic tension between the growing awareness that 'all is interconnected' on the one hand and the realization we cannot take all into account. [ABSTRACT FROM AUTHOR]

Predicted climate change may significantly affect drinking water supply in urban areas. Local water stakeholders facing climate change will have to deal with uncertain information and unexpected events. To address this lack of data, the knowledge and experience of practitioners might be used to assess the potential impacts of climate change on different issues, including drinking water supply. This paper proposes a participatory approach to identify local issues associated with drinking water supply (from source to tap) in a climate change context. This approach relies on the experience and knowledge of local practitioners. The proposed approach was applied to the Québec City metropolitan area (Province of Quebec, Canada). It is based on assignment examples (in this case, a selected set of districts from the study territory) in order to generalize application to the entire territory. This approach helps stakeholders to rationally consider different dimensions and the complexity of drinking water supply. [ABSTRACT FROM AUTHOR]

This paper quantifies the vulnerability of and risk to water resources (VRWR) under a scenario of climate change in the arid and semi-arid region of West China. A new approach integrating hazard, sensitivity, resilience, exposure and risk is developed to assess the VRWR from climate change. Drought is regarded as the key hazard, with its frequency and severity defined using a surface humidity index. Exposure is quantitatively linked with indicators of population and social and economic characteristics using statistical and Geographical Information System (GIS) methodologies. Risk is defined as the product of hazard, exposure and vulnerability, while vulnerability is treated as a function of sensitivity and adaptation. Vulnerability and risk in the water resources system in the coming 20 years are assessed for the RCP 4.5 scenario. The results reveal that both hazard and exposure of water resources display strong spatial variation in the study area. High hazard and exposure are found in the northern Tianshan Mountain as well as the eastern part of Hexi Corridor. Water resources are particularly sensitive to variation in precipitation and potential evapotranspiration in the upstream areas of Hexi Corridor, rivers in Central Asia, headwater streams of Tarim River and most of Chang Tang Plateau. Our assessment shows that there is high vulnerability of and risk to water resources in the study area, especially in the areas of Hexi Corridor, northern Tianshan Mountain and Tarim River. Under the RCP 4.5 climate change scenario, the vulnerability and risk decline over the entire area but remain at a serious level in inland rivers in Hexi Corridor, northern Tianshan Mountain and headwater streams of Tarim River. Thus, these areas are the highest priority for strengthening policy measures to adapt to climate change and reduce exposure and vulnerability and their risk to water resources. [ABSTRACT FROM AUTHOR]

This paper presents a global scale assessment of the impact of climate change on water scarcity. Patterns of climate change from 21 Global Climate Models (GCMs) under four SRES scenarios are applied to a global hydrological model to estimate water resources across 1339 watersheds. The Water Crowding Index (WCI) and the Water Stress Index (WSI) are used to calculate exposure to increases and decreases in global water scarcity due to climate change. 1.6 (WCI) and 2.4 (WSI) billion people are estimated to be currently living within watersheds exposed to water scarcity. Using the WCI, by 2050 under the A1B scenario, 0.5 to 3.1 billion people are exposed to an increase in water scarcity due to climate change (range across 21 GCMs). This represents a higher upper-estimate than previous assessments because scenarios are constructed from a wider range of GCMs. A substantial proportion of the uncertainty in the global-scale effect of climate change on water scarcity is due to uncertainty in the estimates for South Asia and East Asia. Sensitivity to the WCI and WSI thresholds that define water scarcity can be comparable to the sensitivity to climate change pattern. More of the world will see an increase in exposure to water scarcity than a decrease due to climate change but this is not consistent across all climate change patterns. Additionally, investigation of the effects of a set of prescribed global mean temperature change scenarios show rapid increases in water scarcity due to climate change across many regions of the globe, up to 2 °C, followed by stabilisation to 4 °C. [ABSTRACT FROM AUTHOR]

This paper is among the first to report on the full integration of basin-scale models that include projections of the demand and supply of water and energy for residential, commercial, industrial, and agricultural sector users. We link two widely used regional planning models that allow one to study the impact of rising climate variability on water and electricity use in Sacramento, California. Historic data combined with the current energy and water system configuration was used to assess the implications of changes in temperature and precipitation. Climate simulations suggest that electricity imports to the region would increase during hot dry spells, when regional power production is most constrained. In particular, regional imports of electricity would increase over 35 % in hot dry years, assuming a 4 °C increase in average temperature and a 25 % decrease in average precipitation. [ABSTRACT FROM AUTHOR]

The increase in population and the improvement of life standards are stretching the boundaries between water-energy-land management, and demanding innovative and holistic solutions. This article proposes an approach for increasing the water availability of two or more water basins taking into consideration land use and wind patterns, and was named Land, Water, and Wind Watershed Cycle (L3WC). This approach can be applied to one watershed or a combination of watersheds. In the first case, if wind patterns blow mainly in the opposite direction of the main river flow, plantations with high water demand should be focused on the lowest part of the basin. The transpired moisture would then return to the basin with the wind and possibly increase the water availability of the basin. Applying this method to a series of basins, water is transposed from one basin to another, used for irrigated agriculture, returned to the atmosphere with evapotranspiration and pushed back to the basin where the water was extracted by the wind. Case studies of this methodology are presented in the São Francisco basin and between the Tocantins, Amazonas, and Paraná basins and the São Francisco basin in Brazil. The São Francisco basin was selected because it is located in a dry region, its flow has considerably reduced in the past decade and because the trade winds blow constantly from the ocean into the continent all year around. L3WC is a strategy to plan the allocation of water consumption in a watershed, taking into account wind patterns to support the sustainable development of a region. It has the potential of increasing water availability and creating a climate change adaptation mechanism to control the climate and reduce vulnerability to climatic variations. [ABSTRACT FROM AUTHOR]

Climate change models project declining soil moisture levels across the continental US, even in regions with expected increases in annual average precipitation. Although warmer air has been shown to result in more frequent and severe precipitation events, higher vapor pressure deficits are anticipated to result in evapotranspiration rates that exceed the amount of water hitting the soil surface. Numerous analyses have shown rising degrees of aridity in many US locations, even without declining rainfall. The Mid-Atlantic region has less annual rainfall variability and seasonality relative to other areas, and an analysis is presented here examining trends from 1980 to 2019 to determine if the region has become more arid as temperatures have warmed. A comparison of evapotranspiration and precipitation trends cannot adequately answer this question, as the timing of rainfall and soil moisture levels determines how much water is absorbed into the ground and utilized by vegetation. A recursive algorithm is developed to calculate water deficits based on the previous day's conditions and amount of precipitation received during that day, excluding rainwater falling on saturated soils from being eligible to recharge the water supply available to vegetation. Trends from the algorithm show that soil moisture levels have increased over the past four decades. This equates to lower overall water demand per hectare in the municipal and agricultural sectors. While the trends may change in coming decades, unlike other US regions, the Mid-Atlantic has become wetter as defined within an agricultural and meteorological context. [ABSTRACT FROM AUTHOR]

Adaptation strategies are essential to manage water demand and ensure optimal use of available water resources under climate change. Identification and prioritization of adaptation options would greatly support decision-making in drought-prone Northwest Bangladesh. This study identified climate adaptation options by literature review and stakeholder consultation, then used multi-criteria analysis to evaluate and prioritize the options. The complexity of the options was also evaluated, specifically social, institutional, and technical obstacles to their local uptake. Seventy-two adaptation options were identified, spanning six sector categories. The options were further classified as in-system dependent, i.e., options that could be implemented by local actors, or as out-system dependent, i.e., options reliant on actions by external actors. Finally, they were defined as on-farm or off-farm strategies. Transboundary cooperation to increase surface water flows was ranked as the overall top-priority option, though this option is very complex and out-system dependent. Integrated water resources management and integrated crop management were the top-ranked options in the water management and crop production management sectors, respectively. Clustering scattered households and offering training programs in on-farm water management were the most and least complex measures, respectively. Stakeholders exhibited a clear preference for higher scale out-system dependent strategies, rather than in-system dependent options focused on changing the agricultural system itself to cope with climate change. Nonetheless, it is recommended that short-term and medium-term planning focus on opportunities to implement achievable adaptation measures within the local agricultural system. Investment in complex, externally dependent strategies is important for long-term planning. [ABSTRACT FROM AUTHOR]

Future climate change will likely impact the multiple freshwater ecosystem services (fES) provided by catchments through their landscapes and river systems. However, there is high spatio-temporal uncertainty on those impacts linked to climate change uncertainty and the natural and anthropogenic interdependencies of water management systems. This study identifies current and future spatial patterns of fES production in a highly managed water resource system in northern India to inform the design and assessment of plausible adaptation measures to enhance fES production in the catchment under uncertain climate change. A water resource systems modelling approach is used to evaluate fES across the full range of plausible future scenarios, to identify the (worst-case) climate change scenarios triggering the greatest impacts and assess the capacity of adaptation to enhance fES. Results indicate that the current and future states of the fES depend on the spatial patterns of climate change and the impacts of infrastructure management on river flows. Natural zones deliver more regulating and cultural services than anthropized areas, although they are more climate-sensitive. The implementation of a plausible adaptation strategy only manages to slightly enhance fES in the system with respect to no adaptation. These results demonstrate that water resource systems models are powerful tools to capture complex system dependencies and inform the design of robust catchment management measures. They also highlight that mitigation and more ambitious adaptation strategies are needed to offset climate change impacts in highly climate-sensitive catchments. [ABSTRACT FROM AUTHOR]

South America contributes to roughly 30% of global runoff to the oceans. Because the regional economy and biodiversity depend significantly on its water resources, assessing potential climate change impacts on the continental water balance is crucial to support water management planning. Here we evaluate the mean alterations of water balance variables and river discharge in South America by the end of this century using two different GHG scenarios (RCP4.5 and RCP8.5). An ensemble comprising 25 global climate models (GCM) from CMIP5 is used to force a continental-scale hydrologic-hydrodynamic model developed for that region. A negative signal with respect to changes in precipitation, evapotranspiration, and runoff is observed on most of the continent. Major decreases in the annual mean discharge are expected for the Orinoco, Tocantins, and Amazon basins, which would be around 8–14% at least (statistically significant – RCP4.5 and RCP8.5, respectively). Only the Uruguay Basin presents a positive trend for the mean discharge. [ABSTRACT FROM AUTHOR]

Reservoirs play a fundamental role in enhancing sustainable development and economic circumstances, especially in areas with limited water resources. Recently, experts in water resources management have been faced with global warming and climate change as two critical issues that are causing serious problems in water resources. Accordingly, the current study attempts to evaluate the future climate change impacts on agricultural reservoir operation. The results indicated an increase in mean long-term temperature, decreased reservoir's inflow, and an increase in the agricultural water requirement for the Jarreh reservoir system in southwestern Iran, during the period of 2025–2054, under the RCP 8.5 scenario. The results also showed a decrease in reliability (37%) and an increase in vulnerability (9%) using standard operation policy (SOP) under future climate conditions. Due to the predicted drought conditions for the study area, a two-dimensional hedging policy is proposed to mitigate the negative effects of climate change. The results of the hedging model indicated an improvement in the performance of indices in comparison with the use of SOP under climate change impacts. Generally, by using the hedging policy, decreased vulnerability (24%) and reduced maximum deficiencies (14%) are expected for future climate changes. [ABSTRACT FROM AUTHOR]

The Cerrado (Brazilian savannah) is one of the few places in the world that has the potential to increase crop production to meet the projected food demand for 2050. However, for agriculture to be sustainable in this region, irrigation must be efficient. This depends on the water stored in small reservoirs, which play an important role in supporting the local economy. The increase in temperature and net radiation predicted by global climate models may increase the evaporation and reduce the availability of water in these small reservoirs. This work assesses the projected impact of climate change on small reservoir evaporation and water availability in the Brazilian savannah using data from the Eta-HadGEM2-ES and Eta-MIROC5 regional climate models under representative concentration pathways (RCP) 4.5 and 8.5. Evaporation increases of 7.3% (1.09 mm/year−1) and 18.4% (2.74 mm/year−1) are projected in RCP 4.5 and RCP 8.5, respectively, by the year 2100. The water stored in reservoirs is projected to decrease in the future, resulting in higher risks of failure in water supply, especially from the smaller reservoirs. Overall, evaporation increases are expected to reduce the availability of water in small reservoirs during the dry season by 5.5% in RCP 4.5 and 10.4% in RCP 8.5. [ABSTRACT FROM AUTHOR]

Groundwater plays a critical supporting role in agricultural production in the California Central Valley (CV). Recent prolonged droughts (notably 2007–2009 and 2012–2016) caused dramatic depletion of groundwater, indicating the susceptibility of the CV's water supply to climate change. To assess the impact of climate change on groundwater storage in the CV, we combined integrated surface water and groundwater models with climate projections from 20 global climate models and thereby explore the vulnerability of CV groundwater under two climate scenarios RCP4.5 and RCP8.5. We found that groundwater has been declining over the past decades (3 km3/year on average during 1950–2009). In the absence of future mitigating measures, this decline will continue, but at a higher rate due to climate change (31% and 39% increase in loss rate under RCP4.5 and RCP8.5). The greatest loss (more than 80% of the total) will occur in the semi-arid southern Tulare region. We performed computational experiments to quantify the relative contribution of future crop water use and headwater inflows to total groundwater storage change. Our results show that, without management changes, continuing declines in future groundwater storage will mainly be attributable to ongoing overuse of groundwater. However, future changes in the seasonality of streamflow into the CV, (small) changes in annual inflows, and increased crop water use in a warmer climate will lead to 40–70% more annual groundwater losses than the current annual average, up to approximately 5 km3/year. [ABSTRACT FROM AUTHOR]

A set of 28 simulations from five regional climate models are used in this study to assess the Great Lakes' water supply from 1953 to 2100 following emissions scenarios RCP4.5 and 8.5 with a focus on bi-weekly changes in the means and extremes of hydrological variables. Models are first evaluated by comparing annual cycles of precipitation, runoff, evaporation and net basin supply (NBS) with observations. Trends in mean values are then studied for each variable using Theil-Sen's statistical test. Changes in extreme conditions are analyzed using generalized extreme values distributions for a reference period (1971–2000) and two future periods (2041–2070 and 2071–2100). Ensemble trend results show evaporation increases of 136 and 204 mm (RCP4.5 and RCP8.5) over the Great Lakes between 1953 and 2100. Precipitation increases by 83 and 140 mm and runoff increases by 68 and 135 mm. Trends are not equally distributed throughout the year as seasonal changes differ greatly. As a result, Great Lakes net basin supply is expected to increase in winter and spring and decrease in summer. Over the entire year, NBS increases of 14 and 70 mm are projected for scenarios RCP4.5 and 8.5 respectively by the year 2100. An analysis of extreme values reveals that precipitation and NBS maxima increase by 11 to 27% and 1 to 9% respectively, while NBS minima decrease by 18 to 29% between 1971–2000 and 2041–2100. [ABSTRACT FROM AUTHOR]

The Greater Horn of Africa region increasingly experiences high risk of water scarcity. A combination of frequent droughts, rapid population growth and rising urbanisation has reduced streamflow and intensified water abstraction, causing water and food shortages. Estimates of future streamflow changes in the region have so far been highly uncertain and evaluations using ground-based measurements are still limited. Here, future streamflow changes are estimated using a distributed hydrological model forced with an ensemble of high-resolution climate simulations produced using the European community Earth-System Model v3.1. The simulated streamflow is evaluated using observed data from 29 stations from river basins across different climate zones in the region. Evaluation results show large sub-regional variations in the performance of simulated streamflow. The sign and magnitude of future streamflow changes vary between climate simulations and river basins, highlighting the uncertainties in the hydrologic projections. Overall, the streamflow projections indicate large (seasonal, long-term mean and extreme) streamflow decreases for all major rivers in Ethiopia and increases in the equatorial parts of the region at the end of the century. The ensemble mean shows a 10 to 25% decrease in the long-term mean flow in Ethiopia and a 10% increase in the equatorial part of the region in 2080s. Similarly, there is a substantial change in high flows in 2080s, with up to − 50% reduction in the northern and 50% increase in the equatorial parts of the region. These findings are critical because the rivers provide water supply to a rapidly changing socio-economy of the region. [ABSTRACT FROM AUTHOR]

The Intergovernmental Panel on Climate Change (IPCC) has put a lot of efforts to describe uncertainties and to judge the confidence level of its major conclusions. Despite a guidance to communicate uncertainty, the assignment of confidence is not sufficiently clear and, thus, hard to be reproduced by the extern community. By conducting a synthesis assessment about the impacts of climate change on the Brazilian water resources, we identified an opportunity to illustrate the characterization of evidence as adopted in IPCC reports. We propose a method to describe the evidence from model outputs wherein the quality and amount of studies, as well as the consistency among their conclusions, are subject of a transparent rating procedure. In summary, the more comprehensive the study in sampling uncertainties, the higher its quality. Likewise, the amount and consistency among conclusions is assigned in a systematic way. The method is applied for synthesizing a collection of 42 peer-reviewed articles. It reveals important aspects about the evidence of the potential impacts of climate change in the Brazilian water resources, such as changes into a drier hydrological regime. However, the use of multi-model ensemble, the evaluation of models, and the observational data is limited. The proposed method enables consistent communication of the degree of evidence in a transparent, traceable, and comprehensive fashion. The method can be used as a tool to support experts on their judgment. The approach is reproducible and can guide synthesis work not only in Brazil but anywhere else. [ABSTRACT FROM AUTHOR]

Single- to multiple-year drought episodes posed significant challenges for agrarian communities across southern Africa during the nineteenth century and hence are widely recorded in a variety of historical documents. However, the ways in which droughts are articulated, and the focus of individual accounts, vary considerably between different authors and historical source types. This study draws on a range of documentary source types—specifically newspapers, letters, reports and diaries—to explore the varied narratives associated with three protracted droughts (those of 1861–1863, 1876–1879 and 1895–1897) that affected large areas of the subcontinent. The analysis spans four case study areas—present day KwaZulu-Natal (South Africa), Lesotho, Malawi and the southern Kalahari (Botswana and South Africa)—which were investigated as part of different interdisciplinary projects. We explore issues common to all case study areas, including (i) how specific drought events are framed and (ii) what is and is not reported about individual droughts across different source types. We conclude that different source types in the subcontinent may be more or less appropriate for addressing the specific objectives of historical climatology, particularly in relation to historical drought. Sources such as newspapers and weather diaries are rich in qualitative and quantitative observations suitable for the reconstruction of temporal and spatial patterns of weather and climate, as well as climate-related natural disasters. In contrast, letters, reports and personal journals, especially those written by missionaries, provide additional qualitative narratives through which to investigate the vulnerability of past societies and economies to climate variations, and to explore past discourses and social representations of climate. While studies of this kind have been published for European and American source types, this is the first systematic exploration of documentary sources for the historical climatology of Africa. It should therefore provide a guide for climate history studies elsewhere in the continent, or other regions where written records are absent prior to the arrival of European colonists. [ABSTRACT FROM AUTHOR]

Recent water resources planning studies have proposed climate adaptation strategies in which infrastructure and policy actions are triggered by observed thresholds or "signposts." However, the success of such strategies depends on whether thresholds can be accurately linked to future vulnerabilities. This study presents a framework for testing the ability of adaptation thresholds to dynamically identify vulnerable scenarios within ensemble projections. Streamflow projections for 91 river sites predominantly in the western USA are used as a case study in which vulnerability is determined by the ensemble members with the lowest 10% of end-of-century mean annual flow. Illustrative planning thresholds are defined through time for each site based on the mean streamflow below which a specified fraction of scenarios is vulnerable. We perform a leave-one-out cross-validation to compute the frequency of incorrectly identifying or failing to identify a vulnerable scenario (false positives and false negatives, respectively). Results show that in general, this method of defining thresholds can identify vulnerable scenarios with low false positive rates (< 10%), but with false negative rates for many rivers remaining higher than random chance until roughly 2060. This finding highlights the tradeoff between frequently triggering unnecessary action and failing to identify potential vulnerabilities until later in the century, and suggests room for improvement in the threshold-setting technique that could be benchmarked with this approach. This testing framework could extend to thresholds defined with multivariate statistics, or to any application using thresholds and ensemble projections, such as long-term flood and drought risk, or sea level rise. [ABSTRACT FROM AUTHOR]

By combining long-term ground-based data on water withdrawal with climate model projections, this study quantifies the compounding effects of human activities and climate change on surface water availability in Iran over the twenty-first century. Our findings show that increasing water withdrawal in Iran, due to population growth and increased agricultural activities, has been the main source of historical water stress. Increased levels of water stress across Iran are expected to continue or even worsen over the next decades due to projected variability and change in precipitation combined with heightened water withdrawals due to increasing population and socio-economic activities. The greatest rate of decreased water storage is expected in the Urmia Basin, northwest of Iran, (varying from ~ − 8.3 mm/year in 2010–2039 to ~ − 61.6 mm/year in 2070–2099 compared with an observed rate of 4 mm/year in 1976–2005). Human activities, however, strongly dominate the effects of precipitation variability and change. Major shifts toward sustainable land and water management are needed to reduce the impacts of water scarcity in the future, particularly in Iran's heavily stressed basins like Urmia Basin, which feeds the shrinking Lake Urmia. [ABSTRACT FROM AUTHOR]

Changing hydroclimatic conditions on the Canadian Prairies include significant shifts in the intensity, duration, and frequency of precipitation events, as well as temperature and seasonal shifts that affect water availability and quality. Concurrently, high-water-use-intensity industrial development, such as solution potash mining, is also lessening availability of timely water resources in agricultural regions and southern Prairie watersheds. This study used a three-pronged approach to (1) incorporate climate change projections within CEA, (2) identify the impact of projected and trending population and industry growth to inform water-balance calculations and recommendations within the study area, and (3) calculate the net impact on water availability of changing hydroclimate on a specific industry (solution potash mining) using a case study methodology for application to the Qu'Appelle Watershed. The results indicate that an implemented process approach is a good option for incorporating climate change models and methods within cumulative effects monitoring and assessment programs, despite challenges associated with regional variance and lack of long-term data. The outcomes of case study development and review indicate a climate change impact (26% difference) on the available water resources anticipated within the area. And combining this with the water-balance approach, it is recommended that water and climate modeling be completed at the regional scale to account for assumptions and scenario/model-based projections. [ABSTRACT FROM AUTHOR]

The probable effect of climate change on the water available for use in Bangladesh is not well known. We calculate monthly water balances for five main regions of Bangladesh to examine the likely impacts of climate change to 2050. We also examine the impact of past and potential future irrigation development. Climate change projections for rainfall in Bangladesh are uncertain, with increased rain in the wet season likely, but decreased rain also possible. Runoff is projected to vary in a manner similar to rainfall. However, assuming no change to the area of crops, all projections result in increases in irrigation water use, which leads to groundwater level declines. The impact of change (whether climate change or development) on water availability and use is greater in the Northwest region than elsewhere. For most water balance terms in most regions, irrigation development (both historic and future) is calculated to have a larger impact than climate change. Climate change is calculated to have a larger impact than irrigation development only on evapotranspiration and runoff, and possibly on groundwater levels. Model sensitivity tests suggest that model uncertainty is less than climate change uncertainty. To reverse lowered groundwater levels, Bangladesh's policy includes greater use of surface water. While we calculate groundwater levels will rise, the viability of the policy may be affected by future changes to upstream use. [ABSTRACT FROM AUTHOR]

The response of West African climate zones to anthropogenic climate change during the late 21st century is investigated using the revised Thornthwaite climate classification applied to ensembles of CMIP5, CORDEX, and higher-resolution RegCM4 experiments (HIRES). The ensembles reproduce fairly well the observed climate zones, although with some notable discrepancies. CORDEX and HIRES provide realistic fine-scale information which enhances that from the coarser-scale CMIP5, especially in the Gulf of Guinea encompassing marked landcover and topography gradients. The late 21st century projections reveal an extension of torrid climates throughout West Africa. In addition, the Sahel, predominantly semi-arid in present-day conditions, is projected to face moderately persistent future arid climate. Similarly, the Gulf of Guinea shows a tendency in the future to experience highly seasonal semi-arid conditions. Finally, wet and moist regions with an extreme seasonality around orographic zones become less extensive under future climate change. Consequently, West Africa evolves towards increasingly torrid, arid and semi-arid regimes with the recession of moist and wet zones mostly because of the temperature forcing, although precipitation can be locally an important factor. These features are common to all multimodel ensembles, a sign of robustness, with few disagreements in their areal extents, and with more pronounced changes in the higher-resolution RCM projections. Such changes point towards an increased risk of water stress for managed and unmanaged ecosystems, and thus add an element of vulnerability to future anthropogenic climate change for West African water management, ecosystem services and agricultural activities. [ABSTRACT FROM AUTHOR]

Coastal areas of the Mekong Delta in Vietnam are increasingly experiencing salinity intrusion in freshwater systems, in part due to climate change induced sea-level rise, compromising agricultural production and domestic water supply. In order to determine which development trajectories could result in resilient agro-ecosystems, a study area in Thanh Phu district, Ben Tre province was selected where the influence of salinity intrusion on agro-ecosystem can be studied along spatial and temporal salinity gradients. The district is divided in three sub-regions: sub-region 3, closest to the coastline, is principally dedicated to brackish-water shrimp farming; more inland, sub-region 2 has a mix of rice-shrimp farming; and further inland, sub-region 1, which is protected from salinity intrusion by a system of dykes, is dedicated principally to rice farming. Household and expert interviews, focus group discussions and a review of policy documents were used to capture historical salinity problems as well as shifts in farming systems. Agricultural activities have changed in the last decades, mainly driven by national-level policies. At present, the development of engineered infrastructures is favoured whereas complementary or alternative solutions to increase the resilience of social-ecological systems with respect to salinity intrusion exist. These include regeneration of coastal ecosystems, agronomic measures, upstream flow control and shifts in agro-ecosystems. The latter would increasingly enable farmers to work under the influence of both saline and freshwater systems allowing income diversification. National authorities have an opportunity to change the business as usual mode of tackling water-related problems including extreme events in the Mekong Delta through infrastructure development by looking at these alternative solutions. [ABSTRACT FROM AUTHOR]