Spatio-temporal cryosphere variations in the headwater river basins of Central Asia

Central Asia is facing a water shortage due to the negative impacts of climate change. Water resources in this region originate mainly in the mountains of Pamir and Tian-Shan due to snow-and glacier melt. Thus, it is important to understand variations in the cryosphere (snow and glaciers) in this region to foster climate change adaptation measures.This study focuses on the analysis of spatio-temporal changes of snow and glaciers in the Amu Darya, Syr Darya and Zerafshan river basins in Central Asia. Due to limited availability of observational network in the region, we used, besides available station data, also remote sensing-based snow cover area data for the period of 2000-2023. As for the glacier change analysis, we used a degree-day modelling approach to assess changes of glacier thickness in the period of 2000-2023. Eight glaciers were chosen for modelling purposes that are all located in the selected eight river basins for this study. Spatio-temporal analysis of snow cover area change show significantly decreasing number of snow cover days above a certain elevation in Upper Amu Darya and Upper Syr Darya river basins. In both river basins, there are regions with up to 40 days less snow coverage between 2000 and 2023. In the Upper Syr Darya river basins this change is observed in the Akshiirak Massif area, whereas in the Amu Darya River Basin, this change is observed in the Murghab area in the far western part of the river basin. Below a certain elevation zone, there are also areas with increased number of snow cover days of up to 10 days. The attribution of this change into meteorological parameters leads to various hypothesis. The modelling results of glacier thickness change was validated against glacier area evolution that was derived using the Landsat images.  In most of the river basins, a maximum of 60-70 meters of ice thickness loss was estimated with an increase of ice thickness of some glaciers in the accumulation area of about 10-15 meters. However, in two of the valley glaciers (Vanch and Zerafshan River Basins), higher amount of glacier thickness loss was estimated in the last 23 years.The study suggests quantified cryosphere changes in the last 23 years for Central Asian region and emphasizes the need for climate change adaptation as the water resources originating in the mountains of the region (water towers) are important for socio-economic stability.