Remote sensing of snow cover variability in Syr Darya headwater catchments and its effects on spring runoff

Abstract

Snow cover in the Tienshan mountains of Central Asia has large impacts on the water supply of downstream regions. In this thesis the influence of snow cover variability on spring runoff as well as trends were investigated for five headwaters of Syr Darya river. Snow cover data was obtained from the Global SnowPack (GSP) for the years 2000 to 2022. The GSP is processed using snow cover data of the Moderate Resolution Imaging Spectrometer (MODIS). Parameters of snow cover duration (SCD) and snow melt timing were put into relation with spring runoff timing, derived from In-situ runoff data. Catchments varied in size, slope, landcover, elevation distribution and glaciation so varying results were expected. Nevertheless, all catchments exhibited a significant reduction of SCD in the snowmelt season of late winter and spring of -0.53 to -0.73 days per year. For two of the catchments this was accompanied by an advance of streamflow timing measures. The more western catchments exhibited longer average SCD and subsequent later spring runoff. However, they also had stronger decreasing trend. Eastern catchments located upstream of the highly populated Fergana Valley had shorter SCD and runoff timing was less dependent on SCD.