Estimation of Seasonal Snow Cover and Glacial Area Changes in Central Asia (Tien Shan) During the Last 50 Years Using NASA ESE Products and In-Situ Data

The project focuses on estimation of changes in snow- and glacial-covered areas and simulation of the central Asia river runoff variability. Snow dominates the central Asia hydrology, accounting for 50-70% of the total precipitation and providing 60% of the total river runoff. The annual runoff of the major Tien Shan rivers is on average 67 km3 yr-1, which includes glacial melt of about 14 km3 Yr-1 (20%). During droughts, the proportion of glacial runoff increases to 40% of the total as a result of decrease in precipitation and increase in glacier melt. Evaluation of glacier changes during the last thirty years in Tien Shan using aerial photography, Hexagon KH-9, Landsat TM, ALOS/ PRISM, ASTER, and SRTM data has revealed glacier covered area reduction of 1,617 km2 (-10.1%), a threefold increase since 1973 in comparison to the rate estimated for 1943-1973 period. The duration of snow melt from the date of maximum snow cover to date of its disappearance reduced by 30 days and in 2007 was equal to 138 days while the seasonal snow covered area in Tien Shan decreased by 15% (approximately 120,000 km2), estimated using AVHRR and MODIS data. The decrease of seasonal snow cover is not a linear process. Further decrease may be accelerated due to increase of rainfall instead of snowfall in early spring months and consequently a lesser heat expenditure for the snowmelt, which initiates early floods and contribute to the warming. The SGRR model based on GIS DEM distributed meteorological and hydrological parameters from 504 Tien Shan stations predicts increased river runoff by 1.05 times in the next 100 years if air temperature will increase by 3°? and precipitation 1.2 times the current levels. Change in precipitation, rather than air temperature, is the main parameter determining river runoff in the Tien Shan. The maximum ratio for predicted river runoff could reach up to 2.2 and the minimum is predicted to be 0.55 times current levels. However, current glacier recession, while initially considered as a positive factor that increased the river flow, at the end causes the runoff to decrease.