Spatial distribution and seasonal occurrence of Aufeis in the Trans-Himalayan Tso Moriri basin, eastern Ladakh, India

Meltwater from the cryosphere is vital for water supply and livelihood security of the local population in the Trans-Himalaya. Due to decreasing glaciers and the increasing variability of seasonal snow cover, periods of water scarcity regularly occur in summer and spring. The widely neglected cryosphere component of aufeis, a seasonal ice body created by successive freezing of flowing water onto the already frozen surface is mainly located along rivers and streams. It stores base flow in winter and supplements river discharge during spring and early summer. Although this particular cryosphere component has been described for sub-polar permafrost regions across the northern hemisphere, only few studies have investigated Trans-Himalayan aufeis formation. Despite its possible importance for local hydrological systems, a better understanding of specific spatio-temporal freezing and melting patterns is lacking. In the study area 27 aufeis fields, which frequently reappear each year in the same places, with an average maximum extent of 9.2 km² in May were mapped, located at a mean elevation of 4700 m a.s.l. Size of individual aufeis fieldsranges from 0.007 km² to 1.7 km². Based on the 13-year monthly average, an accumulation and depletion phase can be differentiated, which are negatively correlated with surface temperature derived from MODIS data. The accumulation period lasts from November until April, with a peak of monthly average area in January and February. Melting starts in May and aufeis fields disappear by the end of July. A slightly increasing trend in the average ice covered area during the freezing period was found, whereas the maximum extent in May is consistent throughout the time-series with only a minor, non-significant downward trend. In addition, correlation analysis between monthly average overflow area and temperature suggests that temperature is an important variable regarding overflow activity. Temperatures above the 13-year average result in larger overflow areas compared to years with lower temperatures, especially during January, February and March whereas lower temperatures are more beneficial for ice formation in November.