Seasonal snow cover regime and historical change in Central Asia from 1986 to 2008

Abstract

A series of statistics describing seasonal Snow Cover Extent and timing in Central Asia (CA) have been derived from AVHRR satellite images for the time period from 1986 to 2008. Analysis of long term mean snow cover statistics shows that the area weighted mean of long term Snow Covering Days (SCD) for the whole CA is 95.2±65.7days. High elevation mountainous areas above 3000m in Altai, Tien Shan and Pamir, which account for about 2.8% of total area in CA, have SCD >240days. Deserts (Karakorum Desert, Taklamakan Desert, Kumtag Desert) and rain shadow areas of major mountains, accounting for 27.0% of total area in CA, have SCD in the range of 0–30days.Factors affecting snow cover distribution have been analyzed using simple linear regression and segmented regression. For plain regions and windward regions, the SCD rate is +5.9days/100m, while for leeward regions, the rate jumps from +0.7days/100m to +10.0days/100m at about 2335m. Latitude affects the SCD, especially in plain regions with insignificant change of elevation, with rates of 9–10days/degree from south to north.The Mann-Kendal test and the Theil-Sen regression methods have been applied to analyze the spatial heterogeneous trends of change of SCD, Snow Cover Onset Date (SCOD), and Snow Cover Melt Date (SCMD). Area weighed mean SCD in the whole CA does not exhibit significant trend of change from 1986 to 2008. Increase of SCD was observed in the northeastern Kazakh Steppe. Low elevation areas below 2000m in Central Tien Shan and Eastern Tien Shan, as well as mid-elevation areas from 1000m to 3000m in Western Tien Shan, Pamiro-Alai and Western Pamir, also experienced increase of SCD, associated with both earlier SCOD and later SCMD. Decrease of SCD was observed in mountainous areas of Altai, Tien Shan and Pamir, and vast areas in plains surrounding the Aral Sea.