Aufeis in High Mountain Asia: Evidence from two endorheic basins (Tso Moriri and Pangong Tso)

Aufeis is a common phenomenon in permafrost and cold regions of the Northern Hemisphere that develops during winter by successive water overflow and freezing on ice-covered surfaces. Most studies on the occurrence and hydrological importance of aufeis focus on North America and Siberia, while research in High Mountain Asia is still in an early phase. However, its widespread occurrence in the Upper Indus Basin, especially in the cold-arid regions of the Trans-Himalaya and the Tibetan Plateau indicates a need for comprehensive analysis.

Two endorheic basins, located at an elevation above 4500 m a.s.l. were selected for an in depth study: Pangong Tso and Tso Moriri covering an area of ~33500 km² and 2350 km², respectively. Based on a time-series analysis of Landsat and Sentinel-2 data for the period 2008–2021, aufeis fields were mapped and their spatial occurrence and temporal patterns were characterized. Derived parameters include the number, maximum area, and topographical parameters, such as elevation and slope. In addition, high altitude wetland areas were classified for both basins in order to explore potential interactions between hydrology and vegetation cover.

More than 1000 aufeis fields covering an area of 88 km² were detected in the Pangong basin. The largest individual aufeis field reached an area of 14 km². The size increases from south to north towards the Tibetan plateau. 50 % are located at an elevational range from 4800 and 5000 m a.s.l.. In the Tso Moriri basin 27 aufeis fields covering a maximum area of 9 km² spreading over an elevational range from 4600 up to 5000 m a.s.l. were detected. Here, the largest individual aufeis spreads over 1.7 km². The accumulation of aufeis fields starts with regular overflow of water between November until April, while aufeis is usually completely melted by the end of July. However, in the Pangong basin 28 aufeis fields remain until the onset of the next accumulation cycle. All of them are located in elevations above 5000 m a.s.l.. In contrast to the Pangong basin, aufeis fields in the Tso Moriri basin are mostly found in close proximity to wetlands, on areas with frequent aufeis accumulation vegetation is almost completely absent. Potential water sources for overflow events are often located close or within the wetland areas, suggesting close hydrological interactions. The study contributes to an improved understanding of aufeis development and distribution in cold-arid environments and will help further comprehensive cryosphere studies in High Mountain Asia and beyond.