Water resources are highly dependent on climatic variations. The quantification of climate change impacts on surface water availability is critical for agriculture production and flood management. The current study focuses on the projected streamflow variations in the transboundary Mangla Dam watershed. Precipitation and temperature changes combined with future water assessment in the watershed are projected by applying multiple downscaling techniques for three periods (2021–2039, 2040–2069, and 2070–2099). Streamflows are simulated by using the Soil and Water Assessment Tool (SWAT) for the outputs of five global circulation models (GCMs) and their ensembles under two representative concentration pathways (RCPs). Spatial and temporal changes in defined future flow indexes, such as base streamflow, average flow, and high streamflow have been investigated in this study. Results depicted an overall increase in average annual flows under RCP 4.5 and RCP 8.5 up until 2099. The maximum values of low flow, median flow, and high flows under RCP 4.5 were found to be 55.96 m³/s, 856.94 m³/s, and 7506.2 m³/s and under RCP 8.5, 63.29 m³/s, 945.26 m³/s, 7569.8 m³/s, respectively, for these ensembles GCMs till 2099. Under RCP 4.5, the maximum increases in maximum temperature (Tmax), minimum temperature (Tmin), precipitation (Pr), and average annual streamflow were estimated as 5.3 °C, 2.0 °C, 128.4%, and 155.52%, respectively, up until 2099. In the case of RCP 8.5, the maximum increase in these hydro-metrological variables was up to 8.9 °C, 8.2 °C, 180.3%, and 181.56%, respectively, up until 2099. The increases in Tmax, Tmin, and Pr using ensemble GCMs under RCP 4.5 were found to be 1.95 °C, 1.68 °C and 93.28% (2021–2039), 1.84 °C, 1.34 °C, and 75.88%(2040–2069), 1.57 °C, 1.27 °C and 72.7% (2070–2099), respectively. Under RCP 8.5, the projected increases in Tmax, Tmin, and Pr using ensemble GCMs were found as 2.26 °C, 2.23 °C and 78.65% (2021–2039), 2.73 °C, 2.53 °C, and 83.79% (2040–2069), 2.80 °C, 2.63 °C and 67.89% (2070–2099), respectively. Three seasons (spring, winter, and autumn) showed a remarkable increase in streamflow, while the summer season showed a decrease in inflows. Based on modeling results, it is expected that the Mangla Watershed will experience more frequent extreme flow events in the future, due to climate change. These results indicate that the study of climate change’s impact on the water resources under a suitable downscaling technique is imperative for proper planning and management of the water resources.

中文翻译：

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巴基斯坦气候变化及其对水资源的影响评估：以曼格拉流域为例

水资源高度依赖于气候变化。气候变化对地表水供应量影响的量化对于农业生产和洪水管理至关重要。目前的研究重点是跨界的曼格拉大坝流域的预计流量变化。通过在三个时期（2021-2039、2040-2069和2070-2099）应用多种降尺度技术，可以预测流域的降水和温度变化以及未来的水评估。通过使用土壤和水评估工具（SWAT）对五个全球循环模型（GCM）的输出及其在两个代表性浓度路径（RCP）下的集合进行模拟。定义的未来流量指标的时空变化，例如基本流量，平均流量，在这项研究中已经研究了高流量。结果表明，直到2099年，RCP 4.5和RCP 8.5下的年均流量总体增加。RCP4.5下的低流量，中位流量和高流量的最大值为55.96 m³ /s、856.94 m ³ / s和7506.2 m ³ / s以及RCP 8.5以下，63.29 m ³ / s，945.26 m ³ / s，7569.8 m ³/ s，直到2099年为止的这些集合GCM。在RCP 4.5下，最高温度（Tmax），最低温度（Tmin），降水（Pr）和年平均流量的最大增加估计为5.3°C，2.0°直到2099年，C分别为128.4％和155.52％。对于RCP 8.5，这些水文计量变量的最大增加分别达到8.9°C，8.2°C，180.3％和181.56％。 ，直到2099年。发现在RCP 4.5下使用整体GCM的Tmax，Tmin和Pr的升高分别为1.95°C，1.68°C和93.28％（2021-2039），1.84°C，1.34°C和75.88。 ％（2040-2069），1.57°C，1.27°C和72.7％（2070-2099）。在RCP 8.5下，使用整体GCM预测的Tmax，Tmin和Pr的增加分别为2.26°C，2.23°C和78.65％（2021-2039），2.73°C，2.53°C和83.79％（2040– 2069），2.80°C，2。63°C和67.89％（2070-2099）。三个季节（春季，冬季和秋季）流量显着增加，而夏季流量减少。根据建模结果，预计由于气候变化，未来Mangla流域将遇到更频繁的极端水流事件。这些结果表明，在适当的降尺度技术下研究气候变化对水资源的影响对于正确地规划和管理水资源至关重要。由于气候变化。这些结果表明，在适当的降尺度技术下研究气候变化对水资源的影响对于正确地规划和管理水资源至关重要。由于气候变化。这些结果表明，在适当的降尺度技术下研究气候变化对水资源的影响对于正确地规划和管理水资源至关重要。