Historical and recent aufeis in the Indigirka River basin (Russia)

A detailed spatial geodatabase of aufeis (or naled in Russian) within the Indigirka River watershed (305 000 km(2)), Russia, was compiled from historical Russian publications (year 1958), topographic maps (years 1970-1980s) and Landsat images (year 2013-2017). Identification of aufeis by late spring Landsat images was performed with a semi-automated approach according to Normalized Difference Snow Index (NDSI) and additional data. After this, a cross-reference index was set for each aufeis field to link and compare historical and satellite-based aufeis datasets. The aufeis coverage varies from 0.26% to 1.15% in different sub-basins within the Indigirka River watershed. The digitized historical archive (Cadastre, 1958) contains the coordinates and characteristics of 896 aufeis fields with a total area of 2064 km(2). The Landsat-based dataset included 1213 aufeis fields with a total area of 1287 km(2). Accordingly, the satellite-derived total aufeis area is 1.6 times less than the Cadastre (1958) dataset. However, more than 600 aufeis fields identified from Landsat images are missing in the Cadastre (1958) archive. It is therefore possible that the conditions for aufeis formation may have changed from the mid-20th century to the present. Most present and historical aufeis fields are located in the elevation band of 1000-1200 m. About 60% of the total aufeis area is represented by just 10% of the largest aufeis fields. Interannual variability of aufeis area for the period of 2001-2016 was assessed for the Bolshaya Momskaya aufeis and for a group of large aufeis fields (11 aufeis fields with areas from 5 to 70 km(2)) in the basin of the Syuryuktyakh River. The results of this analysis indicate a tendency towards an area decrease in the Bolshaya Momskaya aufeis in recent years, while no reduction in Syuryuktyakh River aufeis area was observed.