Projections of precipitation and temperature changes in the Neelam River Basin, western Himalaya: a CMIP6-based assessment under shared socioeconomic pathways

This study assessed the past and future precipitation and temperature changes in the Neelam River basin, which is located in the western Himalayas. The projections of five General Circulation Models (GCMs) from the Coupled Model Intercomparison Project Phase 6 (CMIP6) were used to analyze the future climate change in the basin. The delta change method was used for the bias correction of the GCMs. The anticipated changes in temperature and precipitation for the near future (2021–2050) were computed under three Shared Socioeconomic Pathways (SSPs; SSP2-4.5, SSP3-7.0, and SSP5-8.5) relative to the baseline period (1985‒2014). The Modified Mann-Kendall (MMK) test was used to assess the significance of temperature and precipitation trends, and the Theil-Sen (TS) slope estimator was used to examine the slope of the trends. According to projections made under all SSPs, the average annual precipitation may decrease in the future. The possible reduction of precipitation varies between − 4.56% (under SSP2-4.5) and − 4.77% (under SSP5-8.5). All SSPs showed a significant decrease in future spring precipitation, with rates of -0.49 mm/year, -6.21 mm/year, and − 4.74 mm/year under SSP2-4.5, SSP3-7.0, and SSP5-8.5, respectively. Under all SSPs, both the minimum temperature (TMin) and maximum temperature (TMax) exhibited significant increases, with the most notable increase in annual TMin under SSP5-8.5, at a rate of 0.07 °C/year. The projected changes in precipitation and temperature may result in more frequent and severe droughts, which would negatively affect the ecosystem, crop production, and hydropower generation in Pakistan. This study provides critical insights for policymakers to devise targeted adaptation and mitigation measures for the Neelam River basin to address the impacts of climate change.

本研究针对坐落于西喜马拉雅山脉的尼尔拉姆河流域（Neelam River basin）的历史及未来降水、气温变化展开评估。研究采用耦合模式比较计划第六阶段（Coupled Model Intercomparison Project Phase 6, CMIP6）下的5个通用环流模式（General Circulation Models, GCMs）的预测结果，分析该流域的未来气候变化；并采用增量变化法（delta change method）对GCMs进行偏差校正。以1985–2014年为基准期，在3种共享社会经济路径（Shared Socioeconomic Pathways, SSPs：SSP2-4.5、SSP3-7.0及SSP5-8.5）下，计算得到了近期（2021–2050年）气温与降水的预期变化。研究采用修正曼-肯德尔检验（Modified Mann-Kendall, MMK）评估气温与降水趋势的显著性，并采用希尔-森斜率估计器（Theil-Sen, TS slope estimator）分析趋势斜率。结果显示，所有SSPs情景下，流域年均降水量均可能出现下降；降水的可能减少幅度介于-4.56%（SSP2-4.5情景）与-4.77%（SSP5-8.5情景）之间。所有SSPs情景下，春季降水均呈现显著减少态势，SSP2-4.5、SSP3-7.0及SSP5-8.5情景下的减少速率分别为-0.49 mm/年、-6.21 mm/年及-4.74 mm/年。所有SSPs情景下，最低气温（TMin）与最高气温（TMax）均呈显著上升趋势，其中SSP5-8.5情景下的年均最低气温升幅最为显著，速率达0.07 ℃/年。降水与气温的预测变化或导致干旱发生更频繁、程度更严重，进而对巴基斯坦的生态系统、作物生产及水力发电产生负面影响。本研究可为政策制定者制定针对性的适应与减缓措施，以应对尼尔拉姆河流域的气候变化影响提供关键参考依据。