Spatial Distribution and Evolution of Aeolian Sandy Land in theAreas around Shigatse Peace Airport of Tibet,China since 1975

Based on large number of on-the-spot investigation and four sets of remote-sensing data acquired in 1975,1990,2000 and 2008,and the man-machine interaction method,we studied sandy desertification in nine counties near Tibet's Shigatse Peace Airport,in the middle reaches of the Yarlung Zangbo River Valley.We analyzed the type and distribution of aeolian sandy land and its evolution since 1975 by interpreting Landsat data from 1975,1990,2000 and 2008 using geographic information system(GIS) technology.The purpose is to timely and precisely understand the status,spatial distribution and developmental trend of aeolian sandy land and to provide guidance for future vegetation restoration.The total area of aeolian sandy land in 2008 was 50053.31 hm2,versus 44071.38 hm2 in 1975,46334.59 hm2 in 1990 and 49064.70 hm2 in 2000,representing a 13.57% increase from 1975 to 2008.The areas of aeolian sandy land caused by windblown sediments and wind erosion within 100 km from Shigatse Peace Airport in 2008 totaled 26656.61 hm2 and 8588.06 hm2,respectively,representing 75.63% and 24.37%.The area of aeolian sandy land totaled 21338.54 hm2 within 40 km from the Airport and 14072.70 hm2 between 0 and 20 km from the airport.The area of aeolian sandy land has increased slowly throughout the study period,at a rate of 150.88 hm2/a during 1975-1989,273.01 hm2/a during 1990-1999 and 109.85 hm2/a in the last nine years,representing a gradual slowing.However,the overall rate of expansion since 1990 averaged 175.94 hm2/a.The increased area of aeolian sandy land mainly resulted from the region's harsh climate and fragile environment,combined with a warmer and drier climate that accelerated the desertification process.