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Accurate assessment of water resources at the watershed level is crucial for effective integrated watershed management. While semi-distributed/distributed models require complex structures and large amounts of input data, conceptual models have gained attention as an alternative to watershed modeling. In this paper, the performance of the GR4J conceptual model for runoff simulation in the Gambia watershed at Simenti station is analyzed over the calibration (1981–1990) and validation period (1991–2000 and 2001–2010). The main inputs to conceptual models like GR4J are daily precipitation data and potential evapotranspiration (PET) measured from the same catchment or a nearby location. Calibration of these models is typically performed using the Nash–Sutcliffe daily efficiency with a bias penalty as the objective function. In this case, the GR4J model is calibrated using four optimization parameters. To evaluate the effectiveness of the model's runoff predictions, various statistical measures such as Nash–Sutcliffe efficiency, coefficient of determination, bias, and linear correlation coefficient are calculated. The results obtained in the Gambia watershed at Simenti station indicate satisfactory performance of the GR4J model in terms of forecast accuracy and computational efficiency. The Nash–Sutcliffe (Q) values are 0.623 and 0.711 during the calibration period (1981–1990) and the validation period (1991–2000), respectively. The average annual flow observed during the calibration period is 0.385 mm while it increases with a value of 0.603 mm during the validation period. As for the average flow simulated by the model, it is 0.142 mm during the calibration period (i.e., a delay of 0.142 mm compared to the observed flow), 0.626 mm in the validation period (i.e., an excess of 0.023 mm compared to the observed flow). However, this study is significant because it shows significant changes in all metrics in the watershed sample under different scenarios, especially the SSP245 and SSP585 scenarios over the period 2021–2100. These changes suggest a downward trend in flows, which would pose significant challenges for water management. Therefore, it is clear that sustainable water management would require substantial adaptation measures to cope with these changes. [ABSTRACT FROM AUTHOR]

Arid area is very sensitive to global warming and are extremely vulnerable to climate change. Moreover, the water resources system in the arid area is fragile and will undergo tremendous changes with climate change. Therefore, the interaction of climate and hydrology in arid area has an important impact on the formation of regional microclimate and hydrological changes. Daihai Lake is a typical closed inland lake in arid area of China, and a key area for ecological protection in North China. In this paper, WRF-Hydro model is used to simulate the climate hydrological coupling situation of Daihai Basin from 1980 to 2020, and the coupling results are verified and calibrated by meteorological statistics, runoff calculation and remote sensing analysis. Based on the synopsis of climate and hydrology in the past 40 years, the causes and future trends of the hydrological elements in Daihai Basin are analyzed. Through the analysis, it is found that the interannual variation of precipitation in Daihai Basin is sharp, with 401.75 mm as the average from 1980 to 1994; and drastic fluctuations from 1995 to 2011, with a difference of nearly 400 mm between the interannual maximum and minimum; From 2012 to 2020, the fluctuation is small. Although the interannual variation of evaporation fluctuated, it showed an upward trend with a slope of 8.855 mm/year. The annual average temperature showed an obvious upward trend with a slope of 0.040 °C/year. From 1980 to 2020, the inflow of Daihai Lake shows a downward trend; Since 2013, the runoff into the lake has tended to be flat. Climate change and human activities are the decisive factors leading to the change of water quantity in Daihai, among which human activities play a greater role. Cultivated land irrigation and industrial water use are highly correlated with the lake discharge, and these two factors have a great influence on the lake discharge. If the current agricultural and industrial water consumption does not increase, Daihai still has a lifespan of nearly 120 years. If human activities do not change and any protective measures are not taken in time, under the background of global climate change, the flow of the Daihai Lake into the lake will be reduced to zero in 2025, and the Daihai Lake will completely dry up in 2031–2033. The study of climate hydrological coupling of long time series in Daihai Basin can not only make up for the lack of runoff data, but also provide the basis for water resources management, disaster prevention and mitigation. [ABSTRACT FROM AUTHOR]

The aim of this paper is to understand the historical and future climate change situation using 15 extreme precipitation indices in the Pare watershed of Arunachal Pradesh, India. Historical period (1981–2019) and future period (2021–2050) precipitation data are used to compute extreme precipitation indices in RClimDex software. The Pare watershed was divided into 13 subwatersheds; however, the results of the study showed no significant spatial variation. This study found that majority of the precipitation extreme indices are showing decreasing trends during the historical period and most of them are statistically insignificant at 95% confidence level. Only three indices such as SDII, CWD and MRI are found significant at 0.05 level in the Pare watershed. Though not significant, the annual precipitation amount in the Pare watershed was found decreasing at the rate of 3.3 mm per year during the study period. The trend analysis over the whole watershed indicated significant decreasing trends for CWD and MRI while indicating significant increasing trend for SDII. The representative concentration pathway (RCP) 4.5 and 8.5 projected the extreme precipitation indices in a very similar way. The results of the trend analysis under RCP 8.5 showed significant decreasing trend only at SW10 for the index-moderate rainfall index (MRI). Various cases of RX1DAY and RX5DAY not falling during the months of monsoon were observed in both the historical and future periods. The percentage departures of the monsoon from its annual total had increased in RCP 4.5 and RCP 8.5 scenarios as compared to the historical periods. The results of this climatic investigation suggest that the precipitation regime in the study area had been accompanied and also expected by overall reduction in precipitation amount, milder rainfall events, reduction in monsoon (June–September) rainfall and drier climatic conditions. With the prevalent historical scenario and future projected scenarios of the extreme precipitation indices, the water resource potential in the study area is expected to be greatly reduced, for which the authors seek the attention of various stakeholders in water and allied sectors to come together and discuss on the construction of water conservation structures so that agricultural activities can be expanded and remain sustainable. [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]

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]

The assessment of the impact of climate change on hydrological systems and their water resources, whether at regional or global scale, presents a major challenge in the twenty-first century. Indeed, scientists need to present response elements regarding this climatic variation in order to establish adequate strategies for water resources management. In this context, this study examines the temporal variation of rainfall and its impact on infiltration in the Northern Gafsa Watershed (southwestern Tunisia), characterized by an arid climate. The analysis of the temporal variation of rainfall is based on daily data recorded over the period (1960–2015) at 6 rainfall stations, regularly spread over the study basin. The different components of the hydrological cycle (initial abstraction, infiltration, actual evapotranspiration and runoff) are estimated by WetSpass-M model. The analysis of the daily rainfall data showed that more than half of the daily rainfall contributions are less than 5 mm/day. On the other hand, the results of the WetSpass-M model show that the minimum infiltration rates exceed 40 mm/year, while the maximum actual evapotranspiration does not exceed 108 mm/year despite arid conditions. The maximum runoff and interception rates are 80.1 and 16.9 mm/year successively. Regression models relating monthly infiltration to rainfall and infiltration of previous months were developed. Both calibration and validation phases resulted in reasonably good agreements between infiltration rates estimated by the proposed regression equations and WetSpass-M model. [ABSTRACT FROM AUTHOR]

The Miankaleh wetland, one of the richest ecosystems in the north of Iran, has experienced an unprecedented environmental degradation caused by overexploitation of the water resources and climatic changes in recent years. This research aims to estimate the environmental water requirement (EWR) for the rivers that drain into the wetland. For this purpose, comprehensive data were collected through physiographic, climatic, hydrologic, ecologic, and field studies of the wetland and its drainage basin. To estimate the EWR, we applied several methods including the Tenant, the Eco-deficit, the flow duration curve, the Wetted-Perimeter method, and the physical habitat simulation model (PHABSIM) and the results were evaluated based on the natural discharge of the rivers before retrogression of the Miankaleh wetland. Further, the results showed that the consideration should be given to the Wetted-Perimeter and the PHABSIM Model for estimation of the EWR for the rivers of the Miankaleh wetland given the seasonality of the rivers and hydroclimatic condition of the study area. The mean annual EWR of the rivers was estimated between 0.12 and 2.03 m3/s, which is close to the values of the bank full flows. The current discharge of the rivers are less than the estimated EWR, showing the discharge rates do not meet the water requirement for aquatic species of the Miankaleh wetland [ABSTRACT FROM AUTHOR]

The past few decades have produced a wealth of research investigating the extent and severity of global climate change. Patterns in climate variability and change have been studied at global, continental and regional scales. Trends observed at these larger spatial scales are expected to be observable at smaller scales, although research in this regard has been limited in South Africa. This study presents an investigation into the microclimatic trends of a key catchment in the KwaZulu-Natal province, South Africa, with particular focus on water resources. Long-term (1980–2017) historical daily meteorological data were analysed using the RClimDex software package as well as other multi-temporal regression and time series analyses. Results indicate an overall warming of the study sites between 1 and 4 °C century−1. Atmospheric water vapour pressure was found to be increasing significantly at three of the sites. Total annual rainfall, an important variable for water resources of the catchment, did not display significant change in the catchment but high levels of inter-annual variability were observed. The results of the study indicate that the catchment microclimate has changed, and is changing, but at different rates from global and continental estimates. The study emphasises the importance of catchment scale analyses using ground-based historical meteorological data. [ABSTRACT FROM AUTHOR]

This study demonstrates the importance of considering potential land use and management changes in climate impact research. By taking into account possible trends of economic development and environmental awareness, we assess effects of global warming on water availability and quality in the catchments of four European lagoons: Ria de Aveiro (Portugal), Mar Menor (Spain), Vistula Lagoon (Poland and Russia), and Tyligulskyi Liman (Ukraine). Different setups of the process-based soil and water integrated model (SWIM), representing one reference and four socio-economic scenarios for each study area: the "business as usual", "crisis", "managed horizons", and "set-aside" scenarios are driven by sets of 15 climate scenarios for a reference (1971–2000) and near future (2011–2040) scenario period. Modeling results suggest a large spatial variability of potential impacts across the study areas, due to differences in the projected precipitation trends and the current environmental and socio-economic conditions. While climate change may reduce water and nutrients input to the Ria de Aveiro and Tyligulsyi Liman and increase water inflow to the Vistula Lagoon the socio-economic scenarios and their implications may balance out or reverse these trends. In the intensely managed Mar Menor catchment, climate change has no notable direct impact on water resources, but changes in land use and water management may certainly aggravate the current environmental problems. The great heterogeneity among results does not allow formulating adaptation or mitigation measures at pan-European level, as initially intended by this study. It rather implies the need of a regional approach in coastal zone management. [ABSTRACT FROM AUTHOR]

The variability and uncertainty of water resources associated with climate change are critical issues in arid and semi-arid regions. In this study, we used the soil and water assessment tool (SWAT) to evaluate the impact of climate change on the spatial and temporal variability of water resources in the Bazoft watershed, Iran. The analysis was based on changes of blue water flow, green water flow, and green water storage for a future period (2010–2099) compared to a historical period (1992–2008). The r-factor, p-factor, R2, and Nash–Sutcliff coefficients for discharge were 1.02, 0.89, 0.80, and 0.80 for the calibration period and 1.03, 0.76, 0.57, and 0.59 for the validation period, respectively. General circulation models (GCMs) under 18 emission scenarios from the IPCC's Fourth (AR4) and Fifth (AR5) Assessment Reports were fed into the SWAT model. At the sub-basin level, blue water tended to decrease, while green water flow tended to increase in the future scenario, and green water storage was predicted to continue its historical trend into the future. At the monthly time scale, the 95% prediction uncertainty bands (95PPUs) of blue and green water flows varied widely in the watershed. A large number (18) of climate change scenarios fell within the estimated uncertainty band of the historical period. The large differences among scenarios indicated high levels of uncertainty in the watershed. Our results reveal that the spatial patterns of water resource components and their uncertainties in the context of climate change are notably different between IPCC AR4 and AR5 in the Bazoft watershed. This study provides a strong basis for water supply-demand analyses, and the general analytical framework can be applied to other study areas with similar challenges. [ABSTRACT FROM AUTHOR]

This study intended to estimate the spatial and temporal variation of current and projected water demand and water availability under climate change scenarios in Weyib River basin, Bale mountainous area of Southeastern Ethiopia. Future downscaled climate variables from three Earth System Models under the three RCP emission scenarios were inputted into ArcSWAT hydrological model to simulate different components of water resources of a basin whereas current and projected human and livestock population of the basin is considered to estimate the total annual water demand for various purposes. Results revealed that the current total annual water demand of the basin is found to be about 289 Mm3, and this has to increase by 83.47% after 15 years, 200.67% after 45 years, and 328.78% after 75 years by the 2020s, 2050s, and 2080s, respectively, from base period water demand mainly due to very rapid increasing population (40.81, 130.80, and 229.12% by the 2020s, 2050s, and 2080s, respectively) and climatic variability. The future average annual total water availability in the basin is observed to be increased by ranging from 15.04 to 21.61, 20.08 to 23.34, and 16.21 to 39.53% by the 2020s, 2050s, and 2080s time slice, respectively, from base period available water resources (2333.39 Mm3). The current water availability per capita per year of the basin is about 3112.23 m3 and tends to decline ranging from 11.78 to 17.49, 46.02 to 47.45, and 57.18 to 64.34% by the 2020s, 2050s, and 2080s, respectively, from base period per capita per year water availability. This indicated that there might be possibility to fall the basin under water stress condition in the long term. [ABSTRACT FROM AUTHOR]

Climate change could significantly influence seasonal streamflow and water availability in the snowpack-fed watersheds of Washington, USA. Descriptions of snowpack decline often use linear ordinary least squares (OLS) models to quantify this change. However, the region's precipitation is known to be related to climate cycles. If snowpack decline is more closely related to these cycles, an OLS model cannot account for this effect, and thus both descriptions of trends and estimates of decline could be inaccurate. We used intervention analysis to determine whether snow water equivalent (SWE) in 25 long-term snow courses within the Olympic and Cascade Mountains are more accurately described by OLS (to represent gradual change), stationary (to represent no change), or step-stationary (to represent climate cycling) models. We used Bayesian information-theoretic methods to determine these models' relative likelihood, and we found 90 models that could plausibly describe the statistical structure of the 25 snow courses' time series. Posterior model probabilities of the 29 'most plausible' models ranged from 0.33 to 0.91 (mean = 0.58, s = 0.15). The majority of these time series (55 %) were best represented as step-stationary models with a single breakpoint at 1976/77, coinciding with a major shift in the Pacific Decadal Oscillation. However, estimates of SWE decline differed by as much as 35 % between statistically plausible models of a single time series. This ambiguity is a critical problem for water management policy. Approaches such as intervention analysis should become part of the basic analytical toolkit for snowpack or other climatic time series data. [ABSTRACT FROM AUTHOR]

Background: Land use/cover and climate changes have a great influence on the hydrological processes in the watershed. The impacts of land use/cover and climate change are set to increase in the future due to the increased clearance of virgin forest lands for agriculture and the rise of global warming. The way in which the future climate will interact with the land use changes and affect the water balance in the watersheds requires more attention. This study was carried out in the Ndembera river watershed in Usangu basin, Tanzania, whereby the Soil and Water Assessment Tool was used to (i) assess the impact of near future (2010-2039) climate and 2013-2020 land use/cover change on the water balance and streamflow and (ii) evaluate the effectiveness of four land and water management practices as the mitigation and adaptation strategies for the impacts of climate and land use/cover changes. The 2020 land use/cover was predicted using Markov Chain and Cellular Automata models based on 2006 and 2013 land use/covers. The near-future climate scenario was generated from the Coupled Model Intercomparison Project 5 General Circulation Models.Results: During the period from 2013 to 2020, the agricultural land and evergreen forests will increase by nearly 10 and 7%, respectively. Mixed forests will decrease by 12%. Such land use/cover changes will decrease the total water yield by nearly 13% while increasing evapotranspiration and surface runoff by approximately 8 and 18%, respectively. This moisture balance changes will be aggravated by warmer near-future mean annual temperatures (1.1 °C) and wetter conditions (3.4 mm/year) than in the baseline period (1980-2009). The warmer future climate will increase evapotranspiration and decrease water yield by approximately 35 and 8%, respectively. The management practices such as filter strips can reduce the annual evapotranspiration by 6%, and increase stream-flow by 38% in February.Conclusion: The future land use/cover changes will interact with the near-future warmer temperatures and reduce water availability in the Ndembera watershed. Land and water management practices have great potential to mitigate the impacts of future climate and land use/cover changes on water resource, thus increasing its availability. [ABSTRACT FROM AUTHOR]