Recent Patterns and Trends in Extreme River Flow Event in the Upper Indus Basin, Pakistan

Abstract

The Upper Indus Basin (UIB), covering the Hindukush, Karakoram, and Himalayan (HKH) ranges, is a key water source for ten major rivers, including Jhelum, Kabul, Hunza, Shyok, and Shigar. This study analyzes trends in high and low streamflows from 1981 to 2016 using the Mann-Kendall test and Sen’s slope estimator to assess their magnitude and timing. The results reveal a decline in high flows across key sub-basins like Jhelum, Indus, and Kabul, while glacier-fed basins such as Shigar and Shyok showed increasing trends. In contrast, nival and rainfall-fed rivers, including Jhelum, Neelum, and Kunhar, exhibited significant negative trends. For low flows, decreasing trends were observed annually and during extreme low-flow periods (one-day, seven-day, fifteen-day), especially in summer. Some stations, however, recorded increased low flows during autumn, winter, and spring. The pronounced decline in summer low flows highlights extended dry periods, raising concerns for water availability during peak demand seasons, which could adversely affect agriculture and hydropower generation in the region.