Study of the impact of climate change on the runoff of the Varzob River Basin in Tajikistan

The Varzob River is one of the main tributaries of the Kofarnihon River and the main water supply of the city of Dushanbe. Changes in water balance, exacerbated by climate change, threaten water security of the whole region. This study aims to study the impact of climate change on the runoff of Varzob River basin using SRM modelling, to simulate the runoff and make predictions. Increasing temperature trends were identified across multiple meteorological stations within the basin in the past decades. Additionally, historical water discharge and precipitation levels indicated weak downward trends. The simulated monthly discharge closely matched the observed values throughout both the calibration and validation periods. On average, the coefficient of determination (R2) value of the simulated annual runoff across all years was 0.925. The average Nash-Sutcliffe model efficiency coefficient (NSE) and the average volume difference (Dv) were 0.8912 and 1.022% respectively during the validation period. According to a simulated climate change scenario, precipitation increase by 10mm leads to rise in runoff by up to 9.57 %. Similarly, another scenario revealed that temperature increase by 2.5 0C leads to an increase in runoff by as high as 5.47 %. The peaks in discharge do not shift under examined climate change scenario. The highest change in discharge occurred during the summer months under both climate change scenarios. The SRM model highlights that climate change significantly impacts precipitation and runoff.