Height dependence of the tendency for reduction in seasonal snow cover in the Himalaya and the Tibetan Plateau region, 1966-2001

The dataset of Northern Hemisphere EASE-Grid Weekly Snow Cover and Sea Ice Extent for the period October 1966 - July 2001 is analyzed to examine the height dependence of declining tendencies of seasonal snow cover in the Himalaya and the Tibetan Plateau region (25-45 degrees N, 70-110 degrees E). It is found that the annual mean snow-covered area is decreasing in the Himalaya/Tibet region at a rate of similar to 1% a(-1), implying that the mean snow-covered area has decreased by one-third from 1966 to 2001. The rate of decrease is largest (1.6%) at the lowest elevations (0-500 m). On the other hand, the length of the snow-cover season is declining at all elevations, with the greatest rate of decline in the 4000-6000 m height range. On the Tibetan Plateau (similar to 4000-6000 m.a.s.l.), the length of the snowcover season has decreased by 23 days, and the end date for snow cover has advanced by 41 days over this 35 year period. These rates might be somewhat overestimated by the binary definition of snow cover on satellite images. It is likely that the reduction of the snow surface albedo by deposition of Asian dust and anthropogenic aerosols may be at least partly responsible for earlier snowmelt.