Changes in monthly streamflow in the Hindukush–Karakoram–Himalaya Region of Pakistan using innovative polygon trend analysis

The present study explored the changes in monthly streamflow in the Hindukush–Karakoram–Himalaya (HKH) region within Pakistan using the recently developed trend analysis method known as innovative polygon trend analysis (IPTA). The monthly streamflow data of 34 gauging stations installed in the HKH region was analyzed, and the Pettitt test was applied to check the homogeneity of the time series. The entire study area was divided into 13 sub-basins, and then changes in monthly streamflow of each sub-basin were explored using the IPTA method. The streamflow of high elevated glaciated and snow/ice-covered sub-basins (e.g., Shyok, Astore, and Chitral) have increased in high flow months (June–August), where there is a downward trend for the Hunza sub-basin in these months. In the Gilgit sub-basin, a transition occurred from no trend in May to a decreasing trend from June to August. The upstream gauges of Swat and Kabul sub-basins showed an increasing trend throughout the year, while downstream gauging stations in the same sub-basins exhibited a strong decreasing trend only in high flow months (June–August). The upper reaches of the Indus part in the Upper Indus Basin (UIB) showed increasing trends in high flow months (June–August), however the downstream gauges of UIB showed decreasing trends throughout the year. Overall, only the glaciated and snow/ice-covered sub-basins experienced increasing trends, while most other sub-basins faced decreasing trends in high flow months and increasing trends in low flow months (October–March). The enhancement of the seasonal pattern of streamflow in the upper reaches of UIB is possibly due to the melting of snow and ice that potentially influence floods and hydropower generation. The results of this study can result in a better understanding of the hydrology of the HKH region and support sustainable water management.