Streamflow Composition and the Contradicting Impacts of Anthropogenic Activities and Climatic Change on Streamflow in the Amu Darya Basin, Central Asia

Transboundary rivers are often the cause of water-related international disputes. One example is the Amu Darya River, with a catchment area of 470 000 km(2), which passes through five countries and provides water resources for 89 million people. Intensified human activities and climate change in this region have altered hydrological processes and led to water-related conflicts and ecosystem degradation. Understanding streamflow composition and quantifying the change impacts on streamflow in the Amu Darya basin (ADB) are imperative to water resources management. Here, a degree-day glacier-melt scheme coupled offline with the Variable Infiltration Capacity hydrological model (VIC-glacier), forced by daily precipitation, maximum and minimum air temperature, and wind speed, is used to examine streamflow composition and changes during 1953-2019. Results show large differences in streamflow composition among the tributaries. There is a decrease in the snowmelt component (-260.8 m(3) s(-1)) and rainfall component (-30.1 m(3) s(-1)) at Kerki but an increase in the glacier melt component (160.0 m(3) s(-1)) during drought years. In contrast, there is an increase in the snowmelt component (378.6 m(3) s(-1)) and rainfall component (12.0 m(3) s(-1)) but a decrease in the glacier melt component (-201.8 m(3) s(-1)) during wet years. Using the VIC-glacier and climate elasticity approach, impacts of human activities and climate change on streamflow at Kerki and Kiziljar during 1956-2015 are quantified. Both methods agree and show a dominant role played by human activities in streamflow reduction, with contributions ranging 103.2%-122.1%; however, the contribution of climate change ranges from -22.1% to -3.2%.