Abstract
The Westerlies and South Asian Monsoon circulation systems play a key role in providing regional freshwater for domestic and agricultural use. As a result of continuous global warming, the spatial and temporal dynamics of these circulation systems have changed. The impact of such changes on the flow of subtropical rivers in the Hindu-Kush mountains of South Asia has not yet been explored, especially near the junction of the Westerlies and the South Asian Monsoon. This study examined the effect of precipitation and temperature variations on flows in the Swat River basin, which is located at the convergence of the two circulations and is one of the main tributaries of the Indus River. The modified Mann-Kendall (MMK) test was used to investigate the historical (1965-2018) patterns of precipitation, temperature and river flow, and the abrupt shifts in flow regimes were analyzed using the sequential Mann-Kendall (SMK) test. Based on the findings of the SMK test, precipitation and temperature series were classified into pre- and post-mutation periods. Results of the MMK test showed that the precipitation, temperature and flow of the basin were increasing significantly. SMK results demonstrated that the significant increase in river flows started after 1984. The average annual flow in the post-mutation period (1985-2018) increased by 33.70% per decade compared with the post-mutation period (1985-2018). In addition, during the post-mutation period, a strong connection between precipitation and streamflow dynamics was found. We can conclude that the increasing tendency of the annual average streamflow in the North Kush mountains is primarily attributable to the increased quantity of regional precipitation.