Predicting hydrologic responses to climate changes in highly glacierized and mountainous region Upper Indus Basin

The Upper Indus Basin (UIB) is a major source of supplying water to different areas because of snow and glaciers melt and is also enduring the regional impacts of global climate change. The expected changes in temperature, precipitation, and snowmelt could be reasons for further escalation of the problem. Therefore, estimation of hydrological processes is critical for UIB. The objectives of this paper were to estimate the impacts of climate change on water resources and future projection for surface water under different climatic scenarios using Soil and Water Assessment Tool (SWAT). The methodology includes: (i) development of SWAT model using land cover, soil and meteorological data; (ii) calibration of the model using daily flow data from 1978-1993; (iii) model validation for the time 1994-2003; (iv) bias correction of Regional Climate Model (v) utilization of bias corrected RCM for future assessment under RCP4.5 and RCP8.5 for mid (2041-2070) and late century (2071-2100). The results of the study revealed a strong correlation between simulated and observed flow with R2 and NSE equals 0.85 each for daily flow. For validation, R2 and NSE were found to be 0.84 and 0.80 respectively. Compared to baseline period (1976-2005), the result of RCM showed an increase in temperature ranging from 2.36°C to 3.50°C and 2.92°C to 5.23°C for RCP4.5 and RCP8.5 respectively, till the end of 21st century. Likewise, the increase in annual average precipitation is 2.4% to 2.5% and 6.0% to 4.6% (mid to late century) under RCP 4.5 and 8.5 respectively. The model simulation results for RCP4.5 showed increase in flow by 19.24% and 16.78% for mid and late century respectively. For RCP8.5, the increase in flow is 20.13% and 15.86% during mid and late century respectively. The model was more sensitive towards available moisture and snowmelt parameters. Thus, SWAT model could be used as effective tool for climate change valuation and for sustainable management of water resources in future.

印度河上游流域（Upper Indus Basin, UIB）是众多地区的重要水源补给地，其水源主要依赖积雪与冰川融水，同时也正承受着全球气候变化带来的区域影响。气温、降水与融雪的预期变化可能会进一步加剧这一问题。因此，对印度河上游流域的水文过程进行精准估算至关重要。
本研究的目标为：利用土壤与水评估工具（Soil and Water Assessment Tool, SWAT），估算气候变化对水资源的影响，并在不同气候情景下开展地表水资源的未来预测。
研究方法包括：
(i) 基于土地覆盖、土壤与气象数据构建SWAT模型；
(ii) 利用1978-1993年的日径流数据对模型进行率定；
(iii) 采用1994-2003年的径流数据完成模型验证；
(iv) 对区域气候模型（Regional Climate Model, RCM）进行偏差校正；
(v) 利用经过偏差校正的RCM，针对典型浓度路径4.5（Representative Concentration Pathway 4.5, RCP4.5）与典型浓度路径8.5（Representative Concentration Pathway 8.5, RCP8.5）情景下的世纪中期（2041-2070年）与世纪末期（2071-2100年）开展未来评估。
研究结果显示，模拟径流与实测径流之间存在极强的相关性，日径流的决定系数（R²）与纳什效率系数（NSE）均为0.85。模型验证阶段的决定系数与纳什效率系数分别为0.84和0.80。相较于基准期（1976-2005年），区域气候模型的结果表明，至21世纪末，RCP4.5情景下气温将升高2.36℃至3.50℃，RCP8.5情景下气温将升高2.92℃至5.23℃。同理，在RCP4.5与RCP8.5情景下，世纪中期至末期的年平均降水量将分别增加2.4%至2.5%与6.0%至4.6%。RCP4.5情景下的模型模拟结果显示，世纪中期与末期的径流量将分别增加19.24%与16.78%；在RCP8.5情景下，世纪中期与末期的径流量将分别增加20.13%与15.86%。该模型对有效水分与融雪参数更为敏感。综上，SWAT模型可作为有效的工具，用于气候变化影响评估以及未来水资源的可持续管理。