Oasis Evolution in the Heihe River Basin during 1956—2010

Taking the aerial photographs(1956) and Landsat MSS(1975),TM ETM+(1990,2000,2005 and 2010) satellite images as the basic data sources,we extracted the information on oasis area and distribution in the Heihe River basin during 1956-2010,and analyzed the driving forces of oasis development.Results showed that:(1) Oasis shrank from 1956 to 1975 and expanded from 1975 to 2010.The area of oasis increased quickly at a high increase rate after 2000,and reached the top level of 8 137.89 km2 in 2010.(2) Oasis was composed of cropland,forest land,wetland,and settlement land in the study area.The cropland together with the forest land occupied about 90% of the oasis,and the cropland took the largest proportion after the year of 1975,which occupied about 60% of the oasis area.(3) Cropland,settlement land expanded gently,but forest land and wetland had an acute change,they expanded and shrank frequently.(4) The natural factors,including arid climate and hydrologic condition,together with the human factors,including population growth,water resources utilization and policy shift,decided the distribution of water resource,and which had a decisive effect on oasis development.