Snow cover characteristics in the Aral Sea Basin from different data sources and their relation with river runoff

Abstract

The snow water equivalent (SWE) and snow depth (SD) in the Aral Sea Basin from the NCEP/DOE, ERA-40 and JRA-25 reanalyses were examined against the measured data. The SWE data from the ERA-40 and SD from the JRA-25 reanalyses demonstrated good agreement with the measured data in the plain part of the Aral Sea Basin in the terms of the mean values (1979–2000) and the correlation coefficients. For the mountain part of the basin, however, the agreement was less consistent, and all the reanalyses tended to underestimate the SWE and SD. The interannual variability of the snow cover area (SCA) from satellite data in the Aral Sea Basin (1971–2006) was also analyzed. The biggest fluctuations of the SCA were observed between 1971 and 1982, and between 1995 and 2005, and the lowest ones during 1983 through 1993. The analysis of the long-term variability of the SD revealed a positive trend during the period from 1930 through 1965 in the upper and middle reaches of the Amudarya and Syrdarya rivers. After 1965, a tendency towards a decrease of the SD in the southern part of the Aral Sea Basin was identified. The analysis of the long-term trends of the SD and the river runoffs in the Amudarya and Syrdarya basins showed that the runoffs of Amudarya and, especially, Syrdarya rivers were increasing, while the SD was mostly decreasing. The SCA in the Aral Sea Basin also exhibited a statistically significant decreasing trend.