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From the Rocky Mountains in the US to the Sea of Cortez in Mexico, the Colorado River is one of the most managed and monitored rivers in the world. As decreasing river flows from drought and climate change continue to impact the Colorado River Basin, the US federal government, seven US states, and Mexico have signed agreements that would reduce deliveries, including a Drought Contingency Plan (DCP), an agreement among the US states and the Bureau of Reclamation, and Minute 323 (a treaty agreement between the US and Mexico). As part of the DCP, the US Bureau of Reclamation (Reclamation) committed to increasing conservation efforts to augment storage in Lake Mead. This paper presents an analysis of Reclamation's Decree Accounting Reports that record water deliveries and conservation savings from 1964 to 2019. Overall, this analysis illustrates that (1) the agency has implemented significant conservation actions over the last three decades, (2) the agency has responded to increased accounting needs as dictated by national and international management agreements, (3) some actions have resulted in environmental costs, and (4) future actions could be designed to avoid environmental harms while also augmenting Lake Mead levels. As climate change continues to constrain Colorado River water supply, detailed accounting may help reveal areas for potential efficiencies or demonstrate where the greatest levels of savings have been reached while ensuring that environmental and social benefits are preserved. Over the last 100 years, humans have changed the path and personality of the Colorado River by distributing water to cities, communities, and agricultural fields to support over 40 million people. Throughout the twentieth century, the US federal government, seven US, and Mexico signed agreements enabling development of Colorado River water. By the early 21st century, as it became evident that water demands and climate change were reducing available supplies, these same governments signed agreements to reduce pressure on the river. All these agreements have, in part, been tracked by the US federal agency that manages the river, the Bureau of Reclamation (Reclamation), through Decree Accounting Reports. Since 1964, these reports have recorded how water is or is not accounted for that might be important to the future of the river. This paper examines those reports and reveals four main findings: (1) Reclamation has implemented numerous water conservation projects, (2) they have responded to new management agreements, (3) some of their actions have impacted the environment, and (4) there are proactive ways they can reduce environmental impacts and bolster water supplies in the future. [ABSTRACT FROM AUTHOR]

Besides existing challenges to water management under scarcity in Africa, climate change has the potential to impose additional pressures on water resources. This study aims at reviewing and identifying the climate change signals presented in 61 peer reviewed papers with respect to seven largest African river basins, viz. Nile, Senegal, Volta, Niger, Congo, Zambezi and Limpopo. Thirty percent of the reviewed papers focussed on the Nile basin while only 13% reported on the Congo basin. The climate change signals were segregated into decreasing, increasing and uncertain trends. Results stated the overwhelming tendency for using unmitigated future emission pathways. The use of ensemble models superiors the individual and synthetic scenarios. While projected temperature showed robust increasing trends, rainfall dominated by uncertain trends. The hydrological impacts were assessed through 19 hydrological models with accepted considerations of land uses at 52% of the cases. Modellers managed to understand and build robust rainfall-runoff relationships in Zambezi, Limpopo, Senegal and partially in Niger but failed in Congo and Nile. Climate change impacts on runoff, stream flows and evapotranspiration should be interpreted cautiously. Further researches are recommended to incorporate the effects of human interventions (e.g. dams) and land use changes in climate change-hydrological modelling. [ABSTRACT FROM AUTHOR]

Climate change impacts on water resources and increasing demand for renewable electricity will have significant impacts on the management of hydroelectric power catchments globally. In New Zealand, where 55% of electricity currently comes from hydroelectricity generation, rainfall over the major South Island hydroelectric power catchments is expected to increase in coming decades, and the seasonality and volatility of that rainfall is expected to change. This paper uses a change factor methodology linked to a model cascade to estimate changes to hydroelectric power catchment inflows in 12 regions of New Zealand. These future river flows are then put through an all of New Zealand electricity system model to examine impacts on flows downstream of the hydroelectric power stations, lake storage, and spill in the large South Island hydroelectric power catchments. An overall 2% increase in annual hydroelectric power catchment inflows over the whole of New Zealand is projected between 2020 and 2050. Seasonal impacts are projected to be larger, with total New Zealand inflows projected to be 10% higher in winter and 6% lower in summer by 2050. Projected changes to inflows are equivalent to between -3% of current total summer New Zealand electricity generation and +5% of winter generation. The four main snow-fed hydroelectric power catchments in the Southern Alps (Pukaki, Tekapo, Clutha, and Manapouri) are predicted to get higher inflows than currently in winter, and lower inflows in summer, with a small increase in annual flows. Modelled changes to inflows and catchment management results in, on average, higher modelled lake storage levels in the snow-fed hydroelectric power catchments in the South Island, which are predicted to spend more time at full lake levels and less time at low lake levels in 2050 than in 2020. The changing inflows, combined with higher storage levels and changes in the electricity system, results in a potential doubling of modelled spill from the large South Island hydroelectric power scheme lakes by 2050. These significant seasonal changes to inflows will better match electricity demand, but the increase to annual spill levels is projected to more than offset any increases in annual inflows over the study period. [ABSTRACT FROM AUTHOR]

The exigency of the current climate crisis demands a more comprehensive approach to addressing location-specific climate impacts. In the Passaic River Basin (PRB), two bodies of research—hydroclimatic trend detection and hydrological modeling—have been conducted with the aim of revealing the basin's hydroclimate patterns as well as the hydrologic response to recent climate change. In a rather novel application of the wavelet transform tool, we sidelined the frequently used Mann–Kendal (MK) trend test, to identify the hidden monotonic trends in the inherently noisy hydroclimatic data. By this approach, the use of MK trend test directly on the raw data, whose results are almost always ambiguous and statistically insignificant in respect of precipitation data, for instance, no longer poses a challenge to the reliability of trend results. Our results showed that, whereas trends in temperature and precipitation are increasing in the PRB, streamflow trends are decreasing. Based on results from the hydrological modeling, streamflow is more sensitive to actual evapotranspiration (ET) than it is to precipitation. In periods spanning decades with sufficient water availability, energy governs actual evapotranspiration rates, rendering streamflow more sensitive to increases in precipitation. Conversely, during meteorologically stressed decades, water availability dictates actual evapotranspiration, consequently amplifying streamflow sensitivity to fluctuations in actual evapotranspiration. We found that the choice of baseline condition constitutes an important source of uncertainty in the sensitivities of streamflow to precipitation and evapotranspiration changes and should routinely be considered in any climate impact assessment. [ABSTRACT FROM AUTHOR]

Water resources are key to economic development of the Mekong River Basin, but are threatened by climate change and affected by hydropower development. Knowledge of these drivers' integrated impact on future hydrological alterations is limited, especially with respect to flood inundation in the lower basin. This study assesses streamflow and flood extent alterations by reservoir operations and climate change using the latest climate projections. A distributed hydrologic model is used to generate discharge and flood extent. Our findings indicate substantial changes in seasonal and annual peak discharge due to reservoir operations. Under the future hydropower scenario, the discharge at Kratie will change by + 28% (− 10%) during the dry (wet) season. While the effects of hydropower operations vary by season, climate change tends to increase river discharge overall. Under the high-emission scenario, the wet seasonal flow at Kratie will increase by + 7% in the near-future (2026–2050), but change by -5% under integrated impact of climate change and reservoir operations. In the far-future, the wet seasonal flow at Kratie under climate change only (integrated impact) will increase by + 33% (+ 19%). Although climate change is the dominant driver of flow alterations, hydropower development is critical for reducing discharge and flood magnitude. Nonparametric statistical testing shows significant changes in the inundated area by up to + 37% during the projected periods. [ABSTRACT FROM AUTHOR]

This paper examines an assessment of the impact of climate change on hydrological regimes and water resources in the basin of Siatista, a sub-basin of the Aliakmon river basin, located in Northern Greece. Initially all acquired hydrometeorological data of the study area, as well as the hydrometric data at the outlet of the basin, were analyzed and processed. A monthly conceptual water balance model was then calibrated using historical hydrometeorological data for determining changes in streamflow runoff under two different equilibrium scenarios (UKHI, CCC) referring to the years 2020, 2050 and 2100. It was found that by applying the two scenarios there will be a reduction of the mean winter runoff values, a serious reduction of summer runoff, an increase of maximum annual runoff and a decrease of minimum annual runoff values, an increase of potential and actual evapotranspiration, leading to a decrease of soil moisture, a reduction of snow accumulation and melting due to temperature increases, resulting in a decrease of spring runoff values and a shifting of the wet period towards December, resulting in severe prolongation of the dry period. [ABSTRACT FROM AUTHOR]

The assessment of the hydrological response to projected changes in climatic variables is imperative for water resources management, especially in watersheds where snowmelt represents a significant source of runoff. In this study, we modify the source code of the snow accumulation and melting algorithm of the Soil and Water Assessment Tool (SWAT) model to improve runoff simulations in snow dominated basins. A sinusoidal snowmelt function under the degree-day factor method was adopted with its parameters calibrated based on historical data. River flow simulations were compared to measured data under the modified and unmodified SWAT models. Model differences in future predictions of river flows (2032- RCP 4.5) were also assessed. The results showed that the modifications improved runoff simulations by better capturing flow dynamics as represented by daily flows and corresponding variability during the snowmelt period. The modified model increased the Nash–Sutcliffe Efficiency (from 0.64 to 0.79; 0.60 to 0.80; 0.70 to 0.75) and the coefficient of determination (from 48 to 67%, 48 to 69%, 58 to 70%) at three gauging stations. While both models predicted a decrease of water availability in the basin, future simulations with the modified snowmelt algorithm predicted that the drop in water availability as compared to baseline year (2008) will be less dramatic (24%) compared to predictions from the unmodified SWAT (31%). We argue that the proposed source code modifications to the snowmelt algorithm of SWAT provide better insights about future water availability in snow-dominated watersheds. [ABSTRACT FROM AUTHOR]

Quantification of the changes of water balance components is significant for water resource assessment and management. This paper employed the Soil and Water Assessment Tool (SWAT) model to estimate the water balance in a mountainous watershed in northwest China at different spatial scales over the past half century. The results showed that both Nash-Sutcliffe efficiency (NSE) and determination coefficient (R2) were over 0.90 for the calibration and validation periods. The water balance components presented rising trends at the watershed scale, and the total runoff increased by 30.5% during 1964 to 2013 period. Rising surface runoff and rising groundwater flow contributed 42.7% and 57.3% of the total rising runoff, respectively. The runoff coefficient was sensitive to increasing precipitation and was not significant to the increase of temperature. The alpine meadow was the main landscape which occupied 51.1% of the watershed and contributed 55.5% of the total runoff. Grass land, forest land, bare land, and glacier covered 14.2%, 18.8%, 15.4%, and 0.5% of the watershed and contributed 8.5%, 16.9%, 15.9%, and 3.2% of the total runoff, respectively. The elevation zone from 3500 to 4500 m occupied 66.5% of the watershed area, and contributed the majority of the total runoff (70.7%). The runoff coefficients in the elevation zone from 1637 to 2800 m, 2800 to 3500 m, 3500 to 4000 m, 4000 to 4500 m, and 4500 to 5062 m were 0.20, 0.27, 0.32, 0.43, and 0.78, respectively, which tend to be larger along with the elevation increase. The quantities and change trends of the water balance components at the watershed scale were calculated by the results of the sub-watersheds. Furthermore, we characterized the spatial distribution of quantities and changes in trends of water balance components at the sub-watershed scale analysis. This study provides some references for water resource management and planning in inland river basins. [ABSTRACT FROM AUTHOR]

Determining the mean transit times (MTTs) and water sources in catchments at different flow conditions helps better understand river functioning, and manage river health and water resources. Despite being common in a range of environments, the MTTs and water sources in intermittent streams are much less well understood compared to perennial streams. Major ion geochemistry, stable isotopes, 14 C, and 3 H were used in this study to identify water sources and MTTs of the periodically intermittent upper Wimmera River from southeast Australia at different flow conditions, including zero-flow periods. The disconnected pool waters during the zero-flow period in the summer months of 2019 had 3 H activities of 0.64 to 3.29 TU. These and the variations in total dissolved solids and stable isotopes imply that these pools contained a mixture of older groundwater and younger stream water impacted by evaporation. 3 H activities during the high-flow period in July 2019 were 1.85 to 3.00 TU, yielding MTTs of up to 17 years. The 3 H activities at moderate and low-flow conditions in September and November 2019 ranged from 2.26 to 2.88 TU, implying MTTs of 1.6 to 7.8 years. Regional groundwater near the Wimmera River had 3 H activities of < 0.02 to 0.45 TU and 14 C activities of 57 to 103 pMC, and was not recharged by the river at high flows. The Wimmera River and other intermittent streams in southeast Australia are sustained by younger catchment waters from relatively small near-river stores than comparable perennial streams, which have older deeper regional groundwater inputs. This results in these intermittent streams being more susceptible to short-term changes in climate and necessitates the protection of near-river corridors to maintain the health of the riverine systems. [ABSTRACT FROM AUTHOR]

Rational allocation of water resources is very essential to cope with water scarcity. The optimal allocation of limited water resources is required for various purposes to achieve sustainable development. The Awash River Basin is currently faced with a scarcity of water due to increasing demands, urbanization, irrigation expansion, and variability of climates. The excessive abstraction of water resources in the basin without proper assessing of the available water resources contributed to water scarcity. This paper aimed to develop a water evaluation and planning (WEAP) model to allocate the water supplies to demanding sectors based on an economic parameter to maximize the economic benefits. The water demands, water shortages, and supply alternatives were analyzed under different scenarios. Three scenarios were developed, namely reference (1981–2016), medium-term development (2017–2030), and long-term development (2031–2050) future scenarios with the baseline period (1980). The results of this study showed that the total quantity of water needed to meet the irrigation demands of all the stations was 306.96 MCM from 1980 to 2016. Seasonally, March, April, May, and June require the maximum irrigation water demand. However, July, August, and September require minimum demand for water because of the rainy season. The seasonal unmet demand is observed in all months, which ranged from 6 × 106 m3 to 35.9 × 106 m3 in August and May respectively. The trend of streamflow in Melka Kuntre was a statistically significant increasing trend after 2008 (Z = 5.33) whereas the trends in other gauge stations showed a relatively decreasing trend. The results also showed that future water consumption would greatly increase in the Awash River Basin. The prevention of future water shortages requires the implementation of water-saving measures and the use of new water supply technologies. The findings of this study will serve as a reference for water resources managers and policy and decision makers. [ABSTRACT FROM AUTHOR]

The influence of climate change on the catchment-scale hydrologic processes can have a profound impact on river flow and the availability of fresh water. Here, we develop an integrated modeling framework to assess the near- and long-term hydrological response to climate change in a mountain river basin. The framework samples climate model outputs under different representative concentration pathways to force the calibrated hydrologic model and generate daily streamflow projections. We implement a framework in the Modi River basin, with an elevation ranging from 750 m to over 8000 m above sea level. Under the highest warming scenario, the mean annual precipitation and temperature are projected to vary to be as high as 4531 mm and 25.7 °C, respectively. The study results show that the future streamflow of the Modi River basin will increase during the latter time windows, i.e., far future (2075–2099) > > mid future (2050–2074) > > near future (2025–2049). Exploring how climate change can alter different hydrological processes can help improve the fundamental understanding of water balance and hydrologic controls, which are critical in ensuring the functionality of the natural ecosystems. [ABSTRACT FROM AUTHOR]

In developing countries with data scarcity challenges, an integrated approach is required to enhance the estimation of streamflow variability for the design of water supply systems, hydropower generation, environmental flows, water allocation and pollution studies. The Flow Duration Curve (FDC) was adopted as a tool that is influenced by topography, land use land cover, discharge and climate change. The data from Global Climate Model (GCM) projections, based on Representative Concentration Pathways (RCP) 4.5 and RCP 8.5 climate scenarios, were used as input data for the SWAT model for the simulation of streamflow. The FDCs were then derived from the simulated streamflow. The FDC for RCP 4.5 showed insignificant differences, whilst for RCP 8.5 it showed an increase of 5–10% in FDC from the baseline period, which is likely to increase the hydropower generation potential with some considerable streamflow variability. The integrated approach of utilizing FDC, GIS and SWAT for the estimation of flow variability and hydropower generation potential could be useful in data scarce regions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Wildfires are becoming more severe and frequent and their effects increasingly expose water resources to stress. • Climate, wildfire, streamflow records (1975 to 2018), topography, and landcover data from 92 catchments were combined to quantify the contribution of wildfire to streamflow variability across Australian temperate forests. • On average wildfire regimes relatively results in 8.8% increases in streamflow across Australian temperate forests. • Wildfire effects on regional streamflow varied spatially depending on hydroclimate factors, particularly precipitation. As wildfires become more frequent and severe, there are concerns regarding their impacts on water yield from forested catchments. While there are many studies in Australia about the effects of individual wildfires on streamflow at fine scales (<1 km2) in specific geographic settings, the effects of wildfire regimes on streamflow at broad spatial scales across temperate forests in Australia are not well understood. In this paper, we combined climate, wildfire, streamflow records (1975 to 2018), topographic, and landcover data from 92 catchments (74 – 4740 km2) in the Australian temperate zone to quantify the contribution of wildfire regimes over time to streamflow variability in different hydroclimatic settings (humid, dry sub-humid, and semi-arid) and geographic regions (Southeast Australia (SEA), Southwest Western Australia (SWWA), and Tasmania (TAS)). Wildfire regimes were represented by two metrics: the burnt area to drainage area (BDA) ratio for wildfire events in each year and a spatially averaged metric of Time Since Fire (TSF), which is a spatial average of time since the last wildfire in the catchment. By comparing prefire and postfire runoff ratios our study found that on average there was a short-term increase in runoff ratio (∼3% in year 1 and ∼6% in year 2 post-fire) after wildfires with BDA > 25%. No influence of fire was found in the long-term (15–20 years after the wildfire) runoff ratio. We found that wildfire regime, measured by TSF, explained ∼8.8% of the variation in annual streamflow across the Australian temperate zone, and that with decreasing TSF (i.e., increased wildfire impact), the average streamflow increased. Streamflow variation explained by wildfire regimes varied with hydroclimate. The explained variance of streamflow by wildfire regimes in semi-arid catchments (23%) and dry sub-humid catchments (13%) were higher than humid catchments (5%). Our results provide a broad-scale understanding of how wildfire regimes influence streamflow variability at broad temporal and spatial scales, and provided important context and baseline information for determining the implications of changes in climate and fire regimes for regional water availability. [ABSTRACT FROM AUTHOR]

Global change is expected to have a strong impact in the Himalayan region. The climatic and orographic conditions result in unique modelling challenges and requirements. This paper critically appraises recent hydrological modelling applications in Himalayan river basins, focusing on their utility to analyse the impacts of future climate and socio-economic changes on water resource availability in the region. Results show that the latter are only represented by land use change. Distributed, process-based hydrological models coupled with temperature-index melt models are predominant. The choice of spatial discretisation is critical for model performance due to the strong influence of elevation on meteorological variables and snow/ice accumulation and melt. However, the sparsity and limited reliability of point weather data, and the biases and low resolution of gridded datasets, hinder the representation of the meteorological complexity. These data limitations often limit the selection of models and the quality of the outputs by forcing the exclusion of processes that are significant to the local hydrology. The absence of observations for water stores and fluxes other than river flows prevents multi-variable calibration and increases the risk of equifinality. The uncertainties arising from these limitations are amplified in climate change analyses and, thus, systematic assessment of uncertainty propagation is required. Based on these insights, transferable recommendations are made on directions for future data collection and model applications that may enhance realism within models and advance the ability of global change impact assessments to inform adaptation planning in this globally important region. [ABSTRACT FROM AUTHOR]

Climate change affects the environment and human life across the planet and it is expected that the negative consequences will be large, especially in developing countries, such as Uzbekistan. The objective of this study was to predict the impact of future climate change on the streamflow of Ugam watershed (Chirchik River Basin (CRB)) using the Soil and Water Assessment Tool (SWAT). The outputs of Coupled Model Intercomparison Project Phase 5 (CMIP5), in combination with Representative Concentration Pathway 8.5, were used as future climate records for the period 2019−2048. The SWAT model was calibrated and validated for the streamflow from Ugam watershed through using the observed daily flow data from 2007 to 2011. The calibrated SWAT model was used to simulate the impact of future climate change on streamflow in the Ugam River for 2019−2048. The results show that the stream discharge is expected to decrease by approximately 42% within thirty years, with a 1.4 °C increase in temperature and 286 mm decrease in precipitation. The peak point for the future period is 40.32 m3 /s in 2037 whereas the lowest discharge, predicted for 2048, accounts for 22.54 m3 /s. Our study enables to understand the impact of climate change on water resources in the Ugam river and to increase the adaptive capacity of water users and managers in the region. [ABSTRACT FROM AUTHOR]

Abstract: Long monthly streamflow series of three control hydrological stations of the Pearl River basin were analyzed by using the scanning t-test and the scanning F-test. Possible implications of the changing properties of streamflow variations for the water resource management of the Pearl River Delta are also discussed. The results indicated that: 1) more complicated changes were observed in terms of the second center moment when compared to the first original moment. More significant abrupt changes of the second center moment imply more sensitive response of streamflow stability to climate changes and human activities; 2) abrupt behaviors of the first (second) center moment of the streamflow variations tend to be more sensitive to climate changes and/or human activities in the larger river basin when compared to those in the smaller river basin. These phenomena are attributed to buffering functions of more storage space of longer river channel, and more complicated and longer runoff yield and concentration processes in the river basin of larger drainage area; 3) annual minimum streamflow of the Pearl River basin tends to be increasing. This will be helpful for better human mitigation of the salinity intrusion in dry seasons across the Pearl River Delta. Annual maximum streamflow, when compared to annual minimum streamflow, shows larger-magnitude variability reflected by larger standard deviation, implying unfavorable conditions for flood mitigation in the Pearl River Delta. The results of this paper are of scientific and practical merits for water resource management and sound human mitigation to water hazards across the Pearl River Delta, and also are a good case study for similar researches in other river deltas in the world under the changing environment. [ABSTRACT FROM AUTHOR]

Summary: Miyun Reservoir is the main raw water source for Beijing’s domestic water supply. Flow discharge to Miyun Reservoir decreased drastically over a 50-year period, from 1956 to 2005, and had seriously affected Beijing’s water supply. Climate variability and human activity had been identified as the two main reasons for the decrease in flow. Here, climate variability refers to changes in precipitation and temperature. Impact of human activity includes direct withdrawal of water (referred to as “direct abstraction” in this paper) from the river (primary) or groundwater and indirect impact due to man-made changes in land use and vegetation in the upstream of the reservoir. According to the historical record, “direct abstraction” from the upstream of the reservoir has increased significantly since 1984. The study period was split into two sub-periods, from 1956 to 1983 and from 1984 to 2005. Based on the historical record, annual runoff in the upstream catchment of Miyun Reservoir (i.e., inflow into the reservoir) had decreased from 90.3mm to 41.8mm for the two sub-periods, a decrease of 48.5mm. Over the same period, average annual “direct abstraction” increased from 2.2mm to 13.4mm, an increase of 11.2mm. The latter accounted for 23% (11.2mm/48.5mm) of the decrease in inflow into the reservoir. This study utilised: (1) a distributed hydrological model (geomorphology-based hydrological model, or GBHM) and (2) a climate elasticity model to conduct a quantitative assessment of the impact of climate variability and the indirect impact of human activity on the inflow into the reservoir. Simulation results of GBHM and the climate elasticity model showed that climate impact was accountable for about 55% and 51% of the decrease in reservoir inflow, respectively. The indirect impact of human activity (mainly man-made land use and vegetation changes) accounted for 18% of the decrease in reservoir inflow. [Copyright &y& Elsevier]

Abstract: The nonparametric Mann–Kendall test was used to detect the trends of major hydroclimatic variables in the Tarim River Basin, the largest inland river basin in China for the period of 1960–2007. Results showed that both mean annual air temperature and precipitation experienced an increasing trend, while annual streamflow demonstrated a mixed trend of decreasing and increasing: The mountainous region upstream showed an increasing trend and the region downstream exhibited a decreasing trend. Impacts of the increased air temperature on streamflow have shown different characteristics depending on location and seasons: it has positive effect on the runoff at mountainous region due to snowmelt and glacier-melt in spring, but negative effect on the runoff at plain area due to the increase of actual evaporation in summer. In addition, human activity contributed to the declining of streamflow in the arid plain oases at downstream of the Tarim River Basin. The results obtained in this paper can be used as a reference for the planning and management of water resources to maintain the health of the river system. [Copyright &y& Elsevier]

Summary: In recent years, climate change impacts on water resources sectors have been extensively documented. Anticipated changes range from more severe storms to more frequent floods and drought at regional scale. Pressure on water resources and hence on the environment will probably increase with the need of quality data for sustainable design of water resources projects. Therefore, for an optimal network design, hydrometric networks are to be reviewed periodically based on the information needs of the various end users and the perspective for future water resources development. This paper evaluates hydrometric networks to identify essential streamflow stations and critical areas (highly poor network density) within major watersheds across the different provinces of Canada using entropy theory. The method is applied to daily streamflow data and information coefficients such as marginal entropy, joint entropy and transinformation index are used for the identification of important stations as well as critical areas in the basin. The analysis results show that almost all Canadian main watersheds contain deficient hydrometric networks. The most deficient streamflow networks are identified in Alberta (North Saskatchewan, Oldman, and Red Deer basins), Northern Ontario (Hudson Bay basin), and the Northwest Territories. The information might prove to be helpful for decision makers to undertake cost-benefit analyses for hydrometric network updating in each region. [Copyright &y& Elsevier]

Climate change has significant effects on societies and ecosystems. Due to the strong link between climate and the hydrological cycle, water resources is one of the most affected fields by climate change. It is of great importance to investigate climate change effects on streamflows by producing future streamflow projections under different scenarios to create adaptation measures and mitigate potential impacts of climate change. The Upper Campaspe Catchment (UCC), located at North Central Victoria in Australia, is a significant catchment as it provides a large portion of total inflow to the Lake Eppalock Reservoir, which supplies irrigation to the Campaspe Irrigation district and urban water to Bendigo, Heathcote, and Ballarat cities. In this study, climate change effects on monthly streamflows in the UCC was investigated using high resolution future climate data from CSIRO and MIROC climate models in calibrated IHACRES hydrological model. The IHACRES model was found to be very successful to simulate monthly streamflow in UCC. Remarkable streamflow reductions were projected based on the climate input from both models (CSIRO and MIROC). According to the most optimistic scenario (with the highest projected streamflows) by the MIROCRCP4.5 model in near future (2035-2064), the Upper Campaspe River will completely dry out from January to May. The worst scenario (with the lowest streamflow projection) by the CSIRO-RCP8.5 model in the far future (2075-2104) showed that streamflows will be produced only for three months (July, August, and September) throughout the year. Findings from this study indicated that climate change will have significant adverse impacts on reservoir inflow, operation, water supply, and allocation in the study area. [ABSTRACT FROM AUTHOR]

This study assesses changes in low flow seasonality in response to climate change using Coupled Model Intercomparison Project Phase 5 (CMIP5) climate models. The precipitation‐runoff modelling system (PRMS) model was applied to project future streamflow using 13 global climate models (GCMs) under two emissions scenarios (representative concentration pathway [RCP] 4.5 and RCP8.5). Then, daily projected streamflows for each month in the reference and future periods were used to assess the monthly variation in low flows in Korean river basins. The results showed that high seasonal variation exists in low flows during the wet and dry seasons, including increasing low flows during the dry season and decreasing low flows during the wet season. The low flows are projected to decrease during the wet season by −6.48% in the 2025 period and by −2.59% in the 2085 period under RCP4.5. Under RCP8.5, the low flow is projected to decline in the wet season by −1.72% in 2025 and −4.35% in 2085. However, during the dry season, the low flow is projected to decrease slightly in the 2025 period (−0.49%) but increase significantly in the 2085 period (12.87%) under RCP4.5. Additionally, the low flow is projected to increase in the near future under RCP8.5 (1.87%). The results reveal that under RCP4.5, most Korean river basins are projected to shift from winter low flows to summer low flows. However, under RCP8.5, except for the Han River basin, which is projected to shift from winter low flows to summer low flows, other basins are expected to retain winter low flows. The findings of this study reveal that more consideration of future low flow conditions is needed, and a robust need exists for the preparation of an adaptation plan to ensure a sustainable water supply to prevent severe water shortages during low flows. [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]

This Special Issue of the journal Water, "The Evaluation of Hydrologic Response to Climate Change", is intended to explore the various impacts of climate change on hydrology. Using a selection of approaches, including field observations and hydrological modeling; investigations, including changing habitats and influences on organisms; modeling of water supply and impacts on landscapes; and the response of varying components of the hydrological cycle, the Issue has published nine articles from multi-institution, often multicountry collaborations that assess these changes in locations around the world, including China, Korea, Russia, Pakistan, Cambodia, United Kingdom, and Brazil. [ABSTRACT FROM AUTHOR]

Hydrological models are widely applied for simulating complex watershed processes and directly linking meteorological, topographical, land-use, and geological conditions. In this study, the Soil and Water Assessment Tool (SWAT) was calibrated at two monitoring stations, which improved model performance and increased the reliability of flow predictions in the Upper Xijiang River Basin. This study evaluated the potential impacts of climate change on the streamflow and water yield of the Upper Xijiang River Basin using Arc-SWAT. The model was calibrated (1991–1997) and validated (1998–2001) using the Sequential Uncertainty Fitting Algorithm (SUFI-2). Model calibration and validation suggest a good match between the measured and simulated monthly streamflow, indicating the applicability of the model for future daily streamflow predictions. Large negative changes of low flows are projected under future climate scenarios, exhibiting a 10% and 30% decrease in water yield over the watershed on a monthly scale. Overall, findings generally indicated that winter flows are expected to be affected the most, with a maximum impact during the January–April period, followed by the wet monsoon season in the May–September period. Water balance components of the Upper Xijiang River Basin are expected to change significantly due to the projected climate change that, in turn, will seriously affect the water resources and streamflow patterns in the future. Thus, critical problems, such as ground water shortages, drops in agricultural crop yield, and increases in domestic water demand are expected at the Xijiang River Basin. [ABSTRACT FROM AUTHOR]

The impact of drought on water resources in arid and semiarid regions can be buffered by water supplies from different source regions. Simultaneous drought in all major source regions — or perfect drought — poses the most serious challenge to water management. We examine perfect droughts relevant to Southern California (SoCal) water resources with instrumental records and tree‐ring reconstructions for the Sacramento and Colorado Rivers, and SoCal. Perfect droughts have occurred five times since 1906, lasting two to three years, except for the most recent event, 2012–2015. This number and duration of perfect droughts is not unusual in the context of the past six centuries. The modern period stands out for the relatively even distribution of perfect droughts and lacks the clusters of perfect drought documented in prior centuries. In comparison, perfect droughts of the 12th Century were both longer (up to nine years) and more widespread. Perfect droughts of the 20th and 21st Centuries have occurred under different oceanic/atmospheric patterns, zonal and meridional flow, and ENSO or non‐ENSO conditions. Multidecadal coherence across the three regions exists, but it has varied over the past six centuries, resulting in irregular intervals of perfect drought. Although the causes of perfect droughts are not clear, given the long‐term natural variability along with projected changes in climate, it is reasonable to expect more frequent and longer perfect droughts in the future. Research Impact Statement: Concurrent or perfect droughts, lasting up to nine years have occurred in the Sacramento and Colorado River Basins, and Southern California over the past nine centuries. [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]

River systems that support high biodiversity profiles are conservation priorities worldwide. Understanding river ecosystem thresholds to low-flow conditions is important for the conservation of these systems. While climatic variations are likely to impact the streamflow variability of many river courses into the future, understanding specific river flow dynamics with regard to streamflow variability and aquifer baseflow contributions is central to the implementation of protection strategies. While streamflow is a measurable quantity, baseflow has to be estimated or calculated through the incorporation of hydrogeological variables. In this study, the groundwater components within the J2000 rainfall–runoff model were distributed to provide daily baseflow and streamflow estimates needed for reserve determination. The modelling approach was applied to the RAMSAR-listed Verlorenvlei estuarine lake system on the west coast of South Africa, which is under threat due to agricultural expansion and climatic fluctuations. The sub-catchment consists of four main tributaries, Krom Antonies, Hol, Bergvallei and Kruismans. Of these, Krom Antonies was initially presumed the largest baseflow contributor, but was shown to have significant streamflow variability attributed to the highly conductive nature of the Table Mountain Group sandstones and Quaternary sediments. Instead, Bergvallei was identified as the major contributor of baseflow. Hol was the least susceptible to streamflow fluctuations due to the higher baseflow proportion (56 %) as well as the dominance of less conductive Malmesbury shales that underlie it. The estimated flow exceedance probabilities indicated that during the 2008–2017 wet cycle average lake inflows exceeded the average evaporation demand, although yearly rainfall is twice as variable in comparison to the first wet cycle between 1987 and 1996. During the 1997–2007 dry cycle, average lake inflows are exceeded 85 % of the time by the evaporation demand. The exceedance probabilities estimated here suggest that inflows from the four main tributaries are not enough to support Verlorenvlei, with the evaporation demand of the entire lake being met only 35 % of the time. This highlights the importance of low-occurrence events for filling up Verlorenvlei, allowing for regeneration of lake-supported ecosystems. As climate change drives increased temperatures and rainfall variability, the length of dry cycles is likely to increase into the future and result in the lake drying up more frequently. For this reason, it is important to ensure that water resources are not over-allocated during wet cycles, hindering ecosystem regeneration and prolonging the length of these dry cycle conditions. [ABSTRACT FROM AUTHOR]

The potential impacts driven by climate variability and urbanization in the Boise River Watershed (BRW), located in southwestern Idaho, are evaluated. The outcomes from Global Circulation Models (GCMs) and land use and land cover (LULC) analysis have been incorporated into a hydrological and environmental modeling framework to characterize how climate variability and urbanization can affect the local hydrology and environment at the BRW. The combined impacts of future climate and LULC change are also evaluated relative to the historical baseline conditions. For modeling exercises, Hydrological Simulation Program‐Fortran (HSPF) is used in parallel computing and statistical techniques, including spatial downscaling and bias correlation, are employed to evaluate climate consequences derived from GCMs as well. The implications of climate variability and land use change driven by urbanization are then observed to evaluate how these overall global challenges can affect water quantity and quality conditions at the BRW. The results show the combined impacts of both climate change and urbanization can lead to more seasonal variability of streamflow (from −27.5% to 12.5%) and water quality, including sediment (from −36.5% to 49.3%), nitrogen (from −24% to 124.2%), and phosphorus (from −13.3% to 21.2%) during summer and early fall over the next several decades. Research Impact Statement: Hydrologic consequences and environmental impacts driven by climate variability and urbanization are critical to develop sustainable water resources planning and management strategies. [ABSTRACT FROM AUTHOR]

Understanding the dominant causes of streamflow alteration and effects of the current water diversion scheme is beneficial for sustainable management of water resources in an arid area. This study presents a quantitative attribution of the run‐off changes between headstreams and mainstream from 1960 to 2015 using the Choudhury–Yang equation and evaluates the effects of 18 times of ecological water conveyance in the lower reaches of the Tarim River Basin (TRB). Our results suggest that climate change was the primary determinant of increase of the streamflow in the headstreams from 2000 to 2015. While in the mainstream, human activities played a dominant role in deduction in the streamflow with the contribution of 54.8–355.6%. Eighteen episodes of ecological water conveyance have a positive effect on rising groundwater level and are highly related to seed falling time of Shrub and Perennial herbaceous and Annual herbaceous except for Arbor. It indicates that restoring the long‐term drying of the lower reaches through continuous water conveyance is feasible, although the existing programme has not restored the entire riparian system. Our study suggests that it is necessary to adopt an integrated approach for water resources allocation rather than relying on a single tributary contribution in the TRB. [ABSTRACT FROM AUTHOR]

Abstract: Streamflow is essential for maintaining healthy aquatic ecosystems and for supporting human water supply needs. Changes in climate, land use and water use practices may alter water availability. Understanding the potential effect of these changes on aquatic ecosystems is critical for long‐term water management to maintain a balance between water for human consumption and ecosystem needs. Fish species data and streamflow estimates from a rainfall‐runoff and flow routing model were used to develop boosted regression tree models to predict the relationship between streamflow and fish species richness (FSR) under plausible scenarios of (1) water withdrawal, (2) climate change and (3) increases in impervious surfaces in the Piedmont ecoregion of North Carolina, U.S.A. Maximum monthly flow, the fraction of total flow originating from impervious surface runoff, coefficient of monthly streamflow variability, and the specific river basin accounted for 50% of the variability in FSR. This model was used to predict FSR values for all twelve‐digit Hydrological Unit Code catchments (HUC‐12s) in the North Carolina Piedmont under current flow conditions and under water withdrawal, climate change and impervious surface scenarios. Flow–ecology modeling results indicate that predicted FSR declined significantly with increased water withdrawals. However, the magnitude of decline varied geographically. A “hot‐spot” analysis was conducted based on predicted changes in FSR under each scenario to understand which HUC‐12s were most likely to be affected by changes in water withdrawals, climate and impervious surfaces. Under the 20% withdrawal increase scenario, 413 of 886 (47%) HUC‐12s in the study area were predicted to lose one or more species. HUC‐12s in the Broad, Catawba, Yadkin and Cape Fear river basins were most susceptible to species loss. These findings may help decision making efforts by identifying catchments most vulnerable to changing water availability. Additionally, FSR‐discharge modeling results can assist resource agencies, water managers and stakeholders in assessing the effect of water withdrawals in catchments to better support the protection and long‐term conservation of species. [ABSTRACT FROM AUTHOR]

Climate change impacts on streamflow and groundwater recharge were evaluated for two nearby watersheds, each with different development pressures and land-use patterns. Dynamically downscaled daily climate projections from a multimodel ensemble were used to drive rainfall-runoff simulations with a distributed hydrologic model. A total of 13 general circulation models (GCMs) with three different emission scenarios were used to analyze the potential impacts of streamflow and recharge in two basins in southern New Jersey. Both basins showed similar responses of streamflow to climate change with increased low flows (95% exceedance). Average annual recharge in the Batsto River basin increased by 5% by 2065, but recharge in the Maurice River basin did not increase based on simulation results. The response of groundwater recharge recharge in the summer was similar in both basins, with simulations indicating a 10–20% increase. It seems likely that different patterns of land use change, population growth, and subsequent changes in water demand will result in different responses to climate change in these basins despite their proximity. In particular, development in the Maurice basin, the need for new stormwater infrastructure, and upgrades to existing infrastructure suggest taking steps towards maximizing retention and groundwater recharge. [ABSTRACT FROM AUTHOR]

The assessment of water resource responses to climate change is required in water resource planning and management, protecting environmental quality, and managing watersheds. This study modeled surface runoff and baseflow responses to variations in precipitation (0%, ±10%, and ±20%) and temperature (0 °C, ±1 °C, and ±2 °C) in 25 types of scenarios in the LanheWatershed (1140 km2), which possesses the typical hydrological and meteorological characteristics of the Loess Plateau in China. The study is based on the Soil and Water Assessment Tool (SWAT), which was calibrated and validated using the coefficient of determination (R2), Nash-Suttcliffe (Ens), and Percent bias (PBIAS), using the observed streamflow of Shangjingyou Station, a unique gauging station in the study area. The model was calibrated with daily streamflow, from 1967 to 1996, and then validated from 1997 to 2011. R2, Ens, and PBIAS were 0.95 and 0.84, 0.78 and 0.72, and 0.6% and -9.1% in annual and monthly calibration periods, 0.90 and 0.78, 0.74 and 0.67, and 22.1% and 18.8% in annual and monthly validation periods, and the overall performance ratings was ?satisfactory?. The assessment indicates that surface runoff is likely to be more affected than baseflow when altering temperatures and precipitation, and the noticeable changes of surface and baseflow are from June to September and October to November, respectively. Results also indicate that surface runoff and baseflow are very sensitive to the projected reduction in temperature, rather than to an increase of temperature, while precipitation is a constant. In turn, when the temperature is a constant, the surface runoff is sensitive to the projected increase in precipitation and the baseflow is sensitive to the decrease in precipitation. [ABSTRACT FROM AUTHOR]

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Water managers across the United States face the need to make informed policy decisions regarding long-term impacts of climate change on water resources. To provide a scientifically informed basis for this, the evolution of important components of the basin-scale water balance through the end of the twenty-first century is estimated. Bias-corrected and spatially downscaled climate projections, from phase 3 of the Coupled Model Intercomparison Project (CMIP3) of the World Climate Research Programme, were used to drive a spatially distributed Variable Infiltration Capacity (VIC) model of hydrologic processes in the Salt-Verde basin in the southwestern United States. From the suite of CMIP3 models, the authors select a five-model subset, including three that best reproduce the historical climatology for the study region, plus two others to represent wetter and drier than model average conditions, so as to represent the range of GCM prediction uncertainty. For each GCM, data for three emission scenarios (A1B, A2, and B1) were used to drive the hydrologic model into the future. The projections of this model ensemble indicate a statistically significant 25% decrease in streamflow by the end of the twenty-first century. The primary cause for this change is due to projected decreases in winter precipitation accompanied by significant (temperature driven) reductions in storage of snow and increased winter evaporation. The results show that water management in central Arizona is highly likely to be impacted by changes in regional climate. [ABSTRACT FROM AUTHOR]

The Upper Indus Basin (UIB) features the high mountain ranges of the Hindukush, Karakoram and Himalaya (HKH). The snow and glacier meltwater contribution feeds 10 major river basins downstream including Astore, Gilgit, Hunza, Jhelum, Kabul, Shyok and Shigar. Climate change is likely to fluctuate the runoff generated from such river basins concerning high and low streamflows. Widening the lens of focus, the present study examines the magnitude and timing of high flows variability as well as trends variability in low streamflows using Sen's slope and the Mann-Kendall test in UIB from 1981 to 2016. The results revealed that the trend in the magnitude of the high flows decreased at most of the sub-basins including the Jhelum, Indus and Kabul River basins. Significantly increased high flows were observed in the glacier regime of UIB at Shigar and Shyok while decreased flows were predominant in Hunza River at Daniyor Bridge. A similar proclivity of predominantly reduced flows was observed in nival and rainfall regimes in terms of significant negative trends in the Jhelum, Kunhar, Neelum and Poonch River basins. The timing of the high flows has not changed radically as magnitude at all gauging stations. For the low flows, decreasing significant trends were detected in the annual flows as well as in other extremes of low flows (1-day, 7-day, 15-day). The more profound and decreasing pattern of low flows was observed in summer at most of the gauging stations; however, such stations exhibited increased low flows in autumn, winter and spring. The decrease in low flows indicates the extension of dry periods particularly in summer. The high-water demand in summer will be compromised due to consistently reducing summer flows; the lower the water availability, the lower will be the crop yield and electricity generation. [ABSTRACT FROM AUTHOR]

An integrated process involving participatory and modelling approaches for prioritizing and evaluating climate change adaptation options for the Kangsabati reservoir catchment is presented here. We assess the potential effects of climate change on water resources and evaluate the ability of stakeholder prioritized adaptation options to address adaptation requirements using the Water Evaluation And Planning (WEAP) model. Two adaptation options, check dams and increasing forest cover, are prioritized using pair-wise comparison and scenario analysis. Future streamflow projections are generated for the mid-21 century period (2021-2050) using four high resolution (~25 km) Regional Climate Models and their ensemble mean for SRES A1B scenario. WEAP simulations indicate that, compared to a base scenario without adaptation, both adaptation options reduce streamflow. In comparison to check dams, increasing forest cover shows greater ability to address adaptation requirements as demonstrated by the temporal pattern and magnitude of streamflow reduction. Additionally, over the 30 year period, effectiveness of check dams in reducing streamflow decreases by up to 40 %, while that of forest cover increases by up to 47 %. Our study highlights the merits of a comparative assessment of adaptation options and we conclude that a combined approach involving stakeholders, scenario analysis, modelling techniques and multi-model projections may support climate change adaptation decision-making in the face of uncertainty. [ABSTRACT FROM AUTHOR]

Recent works have indicated that climate change in the northeastern United States is already being observed in the form of shorter winters, higher annual average air temperature, and more frequent extreme heat and precipitation events. These changes could have profound effects on aquatic ecosystems, and the implications of such changes are less understood. The objective of this study was to examine how future changes in precipitation and temperature translate into changes in streamflow using a physically based semidistributed model, and subsequently how changes in streamflow could potentially impact stream ecology. Streamflow parameters were examined in a New York City water supply watershed for changes from model-simulated baseline conditions to future climate scenarios (2081-2100) for ecologically relevant factors of streamflow using the Indicators of Hydrologic Alterations tool. Results indicate that earlier snowmelt and reduced snowpack advance the timing and increase the magnitude of discharge in the winter and early spring (November-March) and greatly decrease monthly streamflow later in the spring in April. Both the rise and fall rates of the hydrograph will increase resulting in increased flashiness and flow reversals primarily due to increased pulses during winter seasons. These shifts in timing of peak flows, changes in seasonal flow regimes, and changes in the magnitudes of low flow can all influence aquatic organisms and have the potential to impact stream ecology. [ABSTRACT FROM AUTHOR]

The main objective of this research was to study the streamflow evolution of a representative sample of the Spanish near-natural-regime fluvial system over the last four decades of the 20th century. The focus of this study was on those headwater river basins that, not having been subject to substantial human alteration directly via the flow regime, might still have been affected by changes in land management. A representative sample of 74 rivers was selected and a statistical analysis was performed to detect seasonal and annual trends, and the magnitude of streamflow change. Almost all of the rivers studied experienced reductions in streamflow, and three quarters of them had negative and significant (p<0.05) trends in streamflow change. It was impossible to detect any spatial pattern in terms of the type or trend magnitude. The main decreases in the discharge of these near-natural rivers in Spain was observed in the spring and summer, when 81% and 70% of the rivers, respectively, exhibited significant negative trends. The magnitudes of the changes are also remarkable. The average annual percentage change in streamflow magnitude of the 74 basins was –1.45% per year, which corresponds to an average streamflow reduction equivalent to 153 hm3 every year. The results of this study are relevant in view of future climatic scenarios and the evolution of land management in rural and mountain areas, as has already been observed in many parts of the Mediterranean and other regions. Global warming, resulting in continuous temperature increases and therefore evapotranspiration increases, is clearly one factor potentially affecting streamflow, together with land abandonment and subsequent continuous forest expansion. These results obtained in Spain could be extrapolated to other areas in the Mediterranean and beyond and should be taken into account in any water policy and water management in the near future. [ABSTRACT FROM AUTHOR]

Variability of the climate in the headwater drainage basins of the Yangtze River and Yellow River during 1961-2010 was investigated by examining four typical climatic variables: daily minimum, mean, and maximum temperatures and daily precipitation. The results indicate that the temporal trends vary among the climatic variables and the time periods examined. The increase in daily minimum temperature began later than the daily mean and maximum temperatures, but the increase rate of the former was relatively greater after 1985. The abrupt increases in precipitation that occurred near 1978 were much clearer than the three temperature variables. Four dominant periodicities (3, 7, 11, and 18-20 yr) of temperature and precipitation were identified, and these variation patterns directly determined the periodic discharge variations in the two rivers. Under climate change impacts, periodic variations in temperature and precipitation at long temporal scales were intensified after the 1980s. Comparatively, climate change more severely impacts the minimum temperature and precipitation than the maximum and mean temperatures in the study area, and the variability of daily precipitation is more complex than the three temperature variables. Overall, the headwater drainage basin of the Yellow River is more susceptible to climate change compared with the other basin. After 2008, the increase rate of temperature (especially the daily mean and minimum temperatures) became greater, and precipitation showed a downward trend in the study areas. These trends are unfavorable for the safety of water resources and for eco-environmental safety in the two basins. [ABSTRACT FROM AUTHOR]

This contribution analyzes the impact on Iberian water resources of anthropogenic climatic change, using the output from four simulations obtained from two coupled general circulation models (HadCM2 and PCM) under the A2 and B2 emissions scenarios. The results show that the magnitude of those impacts will depend on the level of global warming and the geographical characteristics of each watershed, although a reduction in runoff, principally in spring and summer, and a change in the timing of the maximum discharge, especially in high-altitude basins, will be two the most noteworthy features. [ABSTRACT FROM PUBLISHER]

Over the recent years, several research efforts investigated the impact of climate change on water resources for different regions of the world. The projection of future river flows is affected by different sources of uncertainty in the hydro-climatic modelling chain. One of the aims of the Qbic³ project (Quábec-Bavarian International Collaboration on Climate Change) is to assess the contribution to uncertainty of hydrological models by using an ensemble of hydrological models presenting a diversity of structural complexity (i.e., lumped, semi distributed and distributed models). The study investigates two humid, mid-latitude catchments with natural flow conditions; one located in Southern Quábec (Canada) and one in Southern Bavaria (Germany). Daily flow is simulated with four different hydrological models, forced by outputs from regional climate models driven by global climate models over a reference (1971-2000) and a future (2041-2070) period. The results show that, for our hydrological model ensemble, the choice of model strongly affects the climate change response of selected hydrological indicators, especially those related to low flows. Indicators related to high flows seem less sensitive on the choice of the hydrological model. [ABSTRACT FROM AUTHOR]

Quantitative evaluations of the impacts of climate change on water resources are primarily constrained by uncertainty in climate projections from GCMs. In this study we assess uncertainty in the impacts of climate change on river discharge in two catchments of the Yangtze and Yellow River Basins that feature contrasting climate regimes (humid and semi-arid). Specifically we quantify uncertainty associated with GCM structure from a subset of CMIP3 AR4 GCMs (HadCM3, HadGEM1, CCSM3.0, IPSL, ECHAM5, CSIRO, CGCM3.1), SRES emissions scenarios (A1B, A2, B1, B2) and prescribed increases in global mean air temperature (1 °C to 6 °C). Climate projections, applied to semi-distributed hydrological models (SWAT 2005) in both catchments, indicate trends toward warmer and wetter conditions. For prescribed warming scenarios of 1 C to 6 C, linear increases in mean annual river discharge, relative to baseline (1961-1990), for the River Xiangxi and River Huangfuchuan are +9% and 11% per +1 C respectively. Intra-annual changes include increases in flood (Q05) discharges for both rivers as well as a shift in the timing of flood discharges from summer to autumn and a rise (24 to 93%) in dry season (Q95) discharge for the River Xiangxi. Differences in projections of mean annual river discharge between SRES emission scenarios using HadCM3 are comparatively minor for the River Xiangxi (13 to 17% rise from baseline) but substantial (73 to 121%) for the River Huangfuchuan. With one minor exception of a slight (-2%) decrease in river discharge projected using HadGEM1 for the River Xiangxi, mean annual river discharge is projected to increase in both catchments under both the SRES A1B emission scenario and 2 rise in global mean air temperature using all AR4 GCMs on the CMIP3 subset. For the River Xiangxi, there is substantial uncertainty associated with GCM structure in the magnitude of the rise in flood (Q05) discharges (-1 to 41% under SRES A1B and -3 to 41% under 2 global warming) and dry season (Q95) discharges (2 to 55% under SRES A1B and 2 to 39% under 2° global warming). For the River Huangfuchuan, all GCMs project a rise in the Q05 flow but there is substantial uncertainty in the magnitude of this rise (7 to 70% under SRES A1B and 2 to 57% under 2 global warming). Differences in the projected hydrological changes are associated with GCM structure in both catchments exceed uncertainty in emission scenarios. Critically, estimated uncertainty in projections of mean annual flows is less than that calculated for extreme (Q05, Q95) flows. The common approach of reporting of climate change impacts on river in terms of mean annual flows masks the magnitude of uncertainty in flows that are of most importance to water management. [ABSTRACT FROM AUTHOR]

Clark, Gregory M., 2010. Changes in Patterns of Streamflow From Unregulated Watersheds in Idaho, Western Wyoming, and Northern Nevada. Journal of the American Water Resources Association (JAWRA) 46(3):486-497. DOI: 10.1111/j.1752-1688.2009.00416.x Recent studies have identified a pattern of earlier spring runoff across much of North America. Earlier spring runoff potentially poses numerous problems, including increased risk of flooding and reduced summer water supply for irrigation, power generation, and migratory fish passage. To identify changing runoff patterns in Idaho streams, streamflow records were analyzed for 26 U.S. Geological Survey gaging stations in Idaho, western Wyoming, and northern Nevada, each with a minimum of 41 years of record. The 26 stations are located on 23 unregulated and relatively pristine streams that drain areas ranging from 28 to >35,000 km2. Four runoff parameters were trend tested at each station for both the period of historical record and from 1967 through 2007. Parameters tested were annual mean streamflow, annual minimum daily streamflow, and the dates of the 25th and 50th percentiles of the annual total streamflow. Results of a nonparametric Mann-Kendall trend test revealed a trend toward lower annual mean and annual minimum streamflows at a majority of the stations, as well as a trend toward earlier snowmelt runoff. Significant downward trends over the period of historical record were most prevalent for the annual minimum streamflow (12 stations) and the 50th percentile of streamflow (11 stations). At most stations, trends were more pronounced during the period from 1967 through 2007. A regional Kendall test for water years 1967 through 2007 revealed significant regional trends in the percent change in the annual mean and annual minimum streamflows (0.67% less per year and 0.62% less per year, respectively), the 25th percentile of streamflow (12.3 days earlier), and the 50th percentile of streamflow (11.5 days earlier). [ABSTRACT FROM AUTHOR]

The rainfall-runoff model presented in this study represents the hydrology of 15 major watersheds of the Sierra Nevada in California as the backbone of a planning tool for water resources analysis including climate change studies. Our model implementation documents potential changes in hydrologic metrics such as snowpack and the initiation of snowmelt at a finer resolution than previous studies, in accordance with the needs of watershed-level planning decisions. Calibration was performed with a sequence of steps focusing sequentially on parameters of land cover, snow accumulation and melt, and water capacity and hydraulic conductivity of soil horizons. An assessment of the calibrated streamflows using goodness of fit statistics indicate that the model robustly represents major features of weekly average flows of the historical 1980-2001 time series. Runs of the model for climate warming scenarios with fixed increases of 2°C, 4°C, and 6°C for the spatial domain were used to analyze changes in snow accumulation and runoff timing. The results indicated a reduction in snowmelt volume that was largest in the 1,750-2,750 m elevation range. In addition, the runoff center of mass shifted to earlier dates and this shift was non-uniformly distributed throughout the Sierra Nevada. Because the hydrologic model presented here is nested within a water resources planning system, future research can focus on the management and adaptation of the water resources system in the context of climate change. [ABSTRACT FROM AUTHOR]

The flow of large northern rivers has increased, but regional patterns of changes are not well understood. The aim of this study is the estimation of monthly discharge changes of the 11 river catchments in the Aldan River basin in Eastern Siberia, the largest Lena River tributary and the sixth largest river in Russia. We considered the trend dependence on month, number of years in the sample, finish and start years, and basin area. The median fraction of samples with no trend, positive and negative trends are 70.5%, 28.5%, and 1%, respectively. Longer samples tend to show more positive trends than shorter ones. There is an increasing fraction of samples with positive trends as a function of later sample end year, whereas the start year does not result in a similar pattern. The larger basins, with one exception, have more positive trends than smaller ones. The trends in monthly streamflow have prominent seasonality with absence of positive trends in June and increasing fraction of samples with positive trends from October till April. The study reports the recent streamflow changes on the rarely analyzed rivers in Eastern Siberia, where air temperature rises faster than in average on the globe. The study results are important for water resources management in the region and better understanding of current environmental changes. [ABSTRACT FROM AUTHOR]

The plausible association between climate change and the variability of water resources in the Tarim River basin, west China is investigated in this study. The long-term trend of the hydrological time series including temperature, precipitation, and streamflow are detected by using both parametric and nonparametric techniques. The possible association between the El Niño/Southern Oscillation (ENSO) and these three kinds of time series are tested. This study enhances the knowledge of the climate change impact on water resources in the Tarim River basin. The conclusion obtained in this investigation shows that the temperature experienced a significant monotonic increase at the 5% level of significance during the past 50 yr, and precipitation also exhibited an upward tendency during the past several decades. A significant jump is also detected for both time series around 1986. This may be resulted from the possible impact of climate change, although the interior climate mechanism needs further investigation. Although precipitation and the streamflow from the headwater of the Tarim River exhibited significant increase, decreasing trend has been detected in the streamflow along the mainstream of the river. It implies that anthropogenic activities instead of the climate change dominated the streamflow cessation and the drying-up of the river. Results also showed that no significant association exists between the ENSO and the temperature, precipitation and streamflow in the study area. This conclusion shows that the water curtailment, river desiccation, and ecosystem deterioration in the Tarim River basin may be mainly resulted from the impact of human activities. [ABSTRACT FROM AUTHOR]

Documenting how ground- and surface water systems respond to climate change is crucial to understanding water resources, particularly in the U.S. Great Lakes region, where drastic temperature and precipitation changes are observed. This study presents baseflow and baseflow index (BFI) trend analyses for 10 undisturbed watersheds in Michigan using (1) multi-objective optimization (MOO) and (2) modified Mann–Kendall (MK) tests corrected for short-term autocorrelation (STA). Results indicate a variability in mean baseflow (0.09–8.70 m3/s) and BFI (67.9–89.7%) that complicates regional-scale extrapolations of groundwater recharge. Long-term (>60 years) MK trend tests indicate a significant control of total precipitation (P) and snow- to rainfall transitions on baseflow and BFI. In the Lower Peninsula Rifle River watershed, increasing P and a transition from snow- to rainfall has increased baseflow at a lower rate than streamflow; an overall pattern that may contribute to documented flood frequency increases. In the Upper Peninsula Ford River watershed, decreasing P and a transition from rain- to snowfall had no significant effects on baseflow and BFI. Our results highlight the value of an objectively constrained BFI parameter for shorter-term (<50 years) hydrologic trend analysis because of a lower STA susceptibility. [ABSTRACT FROM AUTHOR]

Climate change plays a pivotal role in the hydrological dynamics of tributaries in the upper Blue Nile basin. The understanding of the change in climate and its impact on water resource is of paramount importance to sustainable water resources management. This study was designed to reveal the extent to which the climate is being changed and its impacts on stream flow of the Gumara watershed under the Representative Concentration Pathway (RCP) climate change scenarios. The study considered the RCP 2.6, RCP 4.5, and RCP 8.5 scenarios using the second-generation Canadian Earth System Model (CanESM2). The Statistical Downscaling Model (SDSM) was used for calibration and projection of future climatic data of the study area. Soil and Water Assessment Tool (SWAT) model was used for simulation of the future stream flow of the watershed. Results showed that the average temperature will be increasing by 0.84 °C, 2.6 °C, and 4.1 °C in the end of this century under RCP 2.6, RCP 4.5, and RCP 8.5 scenarios, respectively. The change in monthly rainfall amount showed a fluctuating trend in all scenarios but the overall annual rainfall amount is projected to increase by 8.6%, 5.2%, and 7.3% in RCP 2.6, RCP 4.5, and RCP 8.5, respectively. The change in stream flow of Gumara watershed under RCP 2.6, RCP 4.5, and RCP 8.5 scenarios showed increasing trend in monthly average values in some months and years, but a decreasing trend was also observed in some years of the studied period. Overall, this study revealed that, due to climate change, the stream flow of the watershed is found to be increasing by 4.06%, 3.26%, and 3.67%under RCP 2.6, RCP 4.5, and RCP 8.5 scenarios, respectively. [ABSTRACT FROM AUTHOR]

Millions of people in Uzbekistan, Turkmenistan, Tajikistan, and Kyrgyzstan are dependent on the freshwater supply of the Vakhsh River system. Sustainable management of the water resources of the Vakhsh River Basin (VRB) requires comprehensive assessment regarding future climate change and its implications for streamflow. In this study, we assessed the potential impacts of projected climate change scenarios on the streamflow in the VRB for two future periods (2022–2060 and 2061–2099). The probable changes in the regional climate system were assessed using the outputs of five global climate models (GCMs) under two representative concentration pathways (RCPs), RCP4.5 and RCP8.5. The probable streamflow was simulated using a semi-distributed hydrological model, namely the Soil and Water Assessment Tool (SWAT). Evidence of a significant increase in the annual average temperature by the end of the 21st century was found, ranging from 2.25 to 4.40 °C under RCP4.5 and from 4.40 to 6.60 °C under RCP8.5. The results of three GCMs indicated a decreasing tendency of annual average precipitation (from −1.7% to −16.0% under RCP4.5 and from −3.4% to −29.8% under RCP8.5). Under RCP8.5, two GCMs indicated an increase (from 2.3% to 5.3%) in the average annual precipitation by the end of 2099. The simulated results of the hydrological model reported an increasing tendency of average annual streamflow, from 17.5% to 52.3% under both RCPs, by the end of 2099. A shift in the peak flow month was also found, i.e., from July to June, under both RCPs. It is expected that in the future, median and high flows might increase, whereas low flow might decrease by the end of 2099. It is concluded that the future seasonal streamflow in the VRB are highly uncertain due to the probable alterations in temperature and precipitation. The findings of the present study could be useful for understanding the future hydrological behavior of the Vakhsh River, for the planning of sustainable regional irrigation systems in the downstream countries, i.e., Uzbekistan and Turkmenistan, and for the construction of hydropower plants in the upstream countries. [ABSTRACT FROM AUTHOR]

The Benue River Basin (BRB) is a major tributary of the Niger River Basin (NRB) and the second-largest river in Cameroon. It serves many water resource functions including irrigation, hydroelectricity production and navigation. Previous research has indicated that recent climate change (CC) has had significant impacts on local and regional hydrological regimes of this watershed. In this study, CC scenarios were integrated with a hydrological model to evaluate the influence of CC on water resources in the BRB. Historical and projected scenarios of dynamically downscaled temperature and precipitation from the REMO regional climate model (RCM) forced by the boundary conditions data of the Europe-wide Consortium Earth System Model (EC-ESM) and the Max Planck Institute-Earth System Model (MPI-ESM) general circulation models (GCMs) were used. The historical runs of the REMO simulations were first evaluated after which downscaled temperature and precipitation data were used as input for the HBV-Light hydrological model to simulate water balance components. The mean climate and hydrological variables for the historical (1981–2005) and the two future periods (2041–2065 and 2071–2095) were compared to assess the potential impact of CC on water resources in the middle and late twenty-first century under three greenhouse gases (GHGs) concentration scenarios, the Representative Concentration Pathways (RCPs) 2.6, 4.5 and 8.5. Our results show that (a) the HBV-Light hydrological model could effectively simulate the streamflow change in the BRB; (b) annual precipitation will decrease between 1 and 10% while both annual temperature and potential evapotranspiration (PET) will increase between 8–18 and 6–30%, respectively, under both scenarios, models and future periods; c) the combination of reduced precipitation and increase of PET results in a significant decrease in streamflow in the BRB (up to 51%) and this will move the basin to a much drier environmental state. Therefore, CC adaptation strategies and future development planning in this region must consider these important decreases of discharge. [ABSTRACT FROM AUTHOR]