Climatic trends variability and concerning flow regime of Upper Indus Basin, Jehlum, and Kabul river basins Pakistan

The Indus Basin is referred to as a “water tower” which ensures water storage and supply to sustain environmental and human needs downstream by a balanced combination of precipitation, snow, glaciers, and surface water. The Upper Indus Basin (UIB) combines the high mountain ranges of the Hindukush, Karakoram, and Himalaya (HKH); this unique region is largely controlled by seasonal meltwater associated with snow and glacier melt during the summer months. The present study seeks to evaluate changes in hydrological and meteorological variable data collected through a network of 35 hydrometric and 15 climatic stations, respectively, across the UIB, Jehlum, and Kabul river basins in Pakistan. The Innovative Trend Significance Test (ITST) in combination with the Modified-Mann-Kendall (MMK) test was used for seeking trends, while Sen’s method was applied for the slope determination of detected trends over four periods of differing lengths ( T 1 : 1961–2013; T 2 : 1971–2013; T 3 : 1981–2013; and T 4 : 1991–2013). Significant decreases were observed in the mean summer and distinct months of (June–August) temperature ( T mean ) at most of the stations during T 1 , while significant increases were dominant over the shorter T 4 . The mean precipitation ( P mean ) was observed as significantly negative at ten stations during July; however, positive trends were observed in August and September. For streamflow, significantly upward trends were observed for mean summer, June and July flows (snowmelt dominant) during T 1 and T 2 , within the glacier-fed basins of Hunza, Shigar, and Shyok; in contrast, streamflow (glacier melt dominant) decreased significantly in August and September over the most recent period T 4 . For snow-fed basins, significant increases were observed in summer mean flows at Indus at Kachura, Gilgit at Gilgit, and Alam Bridge, Astore at Doyian during ( T 1 – T 3 ). In particular, a stronger and more prominent signal of decreasing flows was evident in T 4 within the predominantly snow-fed basins. This signal was most apparent in summer mean flows, with a large number of stations featuring significant downward trends in Jehlum and Kabul river basins. The present study concludes that the vulnerability of this region related to water stress is becoming more intense due to significantly increased temperature, reduced precipitation, and decreasing summer flows during T 4 .