Abstract: Aimed to rationally exploit and utilize the water resources of Heihe River basin and to mitigate the continuous ecoenvironmental deterioration in the middle lower reaches of the basin, Chinese government has implemented water redistribution policy since 2000. Taking the middle reaches of Heihe River basin as study area and based on the information from Landsat ETM/TM data, the land use and land cover data in 1990, 2000, and 2005 were obtained by humancomputer interaction visual interpretation. Through editing these data, the overall situation of land use/cover change in the area was understood, and the changes in the forestland and grassland areas before and after water redistribution were analyzed. The forestland area changed from a slight increase before water redistribution to negative growth after water redistribution, while grassland had a continuous degrada
tion but the degradation speed slowed down after water redistribution. These results fully reflected the effects of implementing water distribution policy on the land use/cover change in this area.

Key words: Soil temperature extremum, Plastic mulch, Bare soil, Cotton, Maize