Aufeis is a common phenomenon in cold regions of the Northern Hemisphere that develops during winter by successive water overflow and freezing on ice-covered surfaces. Most studies on aufeis occurrence focus on regions in North America and Siberia, while research in High Mountain Asia (HMA) is still in an exploratory phase.This study investigates the extent and dynamics of icing processes and aufeis in the Tso Moriri basin, eastern Ladakh, India. Based on a combination of 235 Landsat 5 TM/8 OLI and Sentinel-2 imagery from 2008 to 2021 the occurrence of icing and aufeis was classified using a random forest classifier. A total of 27 frequently occurring aufeis fields with an average maximum extent of 9 km 2 were identified, located at a mean elevation of 4,700 m a.s.l. Temporal patterns show a distinct accumulation phase (icing) between November and April, and a melting phase lasting from May until July. Icing is characterized by high seasonal and inter-annual variability. Successive water overflow mainly occurs between January and March and seems to be related to diurnal freeze-thaw-cycles, whereas higher daytime temperatures result in larger icing areas. Aufeis feeding sources are often located within or in close vicinity to wetland areas, while vegetation is largely absent on surfaces with frequent aufeis formation. These interactions require more attention in future research. In addition,this study shows the high potential of a machine learning approach to monitor icing processes and aufeis, which can be transferred to other regions.
<p><em>Aufeis</em> 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 <em>aufeis</em> 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.</p><p>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 km&#178; and 2350 km&#178;, respectively. Based on a time-series analysis of Landsat and Sentinel-2 data for the period 2008&#8211;2021, <em>aufeis</em> 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.</p><p>More than 1000 <em>aufeis </em>fields covering an area of 88&#160;km&#178; were detected in the Pangong basin. The largest individual <em>aufeis</em> field reached an area of 14&#160;km&#178;. The size increases from south to north towards the Tibetan plateau. 50&#160;% are located at an elevational range from 4800 and 5000&#160;m a.s.l.. In the Tso Moriri basin 27 aufeis fields covering a maximum area of 9&#160;km&#178; spreading over an elevational range from 4600&#160;up to 5000&#160;m a.s.l. were detected. Here, the largest individual <em>aufeis</em> spreads over 1.7 km&#178;. The accumulation of <em>aufeis</em> fields starts with regular overflow of water between November until April, while <em>aufeis</em> is usually completely melted by the end of July. However, in the Pangong basin 28 <em>aufeis </em>fields remain until the onset of the next accumulation cycle. All of them are located in elevations above 5000&#160;m a.s.l.. In contrast to the Pangong basin, <em>aufeis</em> fields in the Tso Moriri basin are mostly found in close proximity to wetlands, on areas with frequent <em>aufeis</em> 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 <em>aufeis</em> development and distribution in cold-arid environments and will help further comprehensive cryosphere studies in High Mountain Asia and beyond.</p>
<p>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 <em>aufeis, </em>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 <em>aufeis</em> formation. Despite its possible importance for local hydrological systems, a better understanding of specific spatio-temporal freezing and melting patterns is lacking.&#160;In the study area 27 <em>aufeis </em>fields, which frequently reappear each year in the same places,<em> </em>with an average maximum extent of 9.2&#160;km&#178; in May were mapped, located at a mean elevation of 4700 m a.s.l. Size of individual <em>aufeis </em>fieldsranges from 0.007&#160;km&#178; to 1.7&#160;km&#178;. 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 <em>aufeis</em> 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.</p>
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