Extreme Hydrometeorological Conditions and Changes in the Amu Darya River Basin in Central Asia

Abstract

The Amu Darya contributed 70% of the flow to the Aral Sea in Central Asia before the 1960s, when the Amu Darya streamflow to the Aral Sea started to dwindle. The severe environmental and socioeconomic disaster happened mainly due to intensified water abstraction with the backdrop of climate change. However, the knowledge of up to the most recent extreme climate conditions and their changes, as well as their relations to streamflow in the basin is still lacking. This study aims to understand extreme hydro-meteorological conditions and their changes, as well as their relations in the past several decades, especially in the upper Amu Darya basin. The spatial patterns of the means of all extreme temperature indices followed the elevation gradient. The majority of the basin showing increasing trend in extreme warm events but decreasing trend in extreme cold events. The north of the upper basin had over 1000 mm annual precipitation, and the east had less than 300 mm annual precipitation. Overall, the upper Amu Darya basin underwent a wetting and warming annual trend. Annual streamflow in the upper sub-basins was less than 750 m3/s, but together they produced over 1500 m3/s flow in the middle reach and basin outlet. Streamflow change varied among sub-basins. Correlations between climatic factors and streamflow at annual time step were weak but distinct at monthly time step with lagged effects. In highland sub-basins with high coverage of glacier and snow, temperature minima and maxima impacts were opposite and overwhelmed precipitation, whereas in lowland sub-basins, precipitation was more important.