Evolution and Variation of Land Desertification in Hiehe River Basin and Its Effection Factors

The status of land desertification in the Heihe River basin was studied using existing remote sensing data and field investigation data.The hydrological characteristics of desertified land in the basin were analysed,which provide a theoretical basis for the rational and sustainable use of water and land resources,and the land desertification cantrol,rehabilitation and reversing in the arid inland river basin of northwest China.Based on the field experiments and indoor analyses this research puts forward the following conclusions. Under the influences of various natural factors including climate,geology,geomorphology,Aeolian sand activity and natural disasters,the Heihe River basin experienced the alternative oasisi expansion and land desertigcation processes in the historival period.In the warm period land desertification weakened,while in te cold period land desertification strongly exacerbated. Reseaches showed that from the mid-1980s to the 1990s land desertification area in Ejina increased by 29.1%.Desertificated land in the midstream basin increased by 9.4% or annual by 0.27%.From 1990 onwards,land desertification tended to become stable. By the 2000 land desertification area in the mid-downstream basin of the Heihe River accounted for 11.8% of the monitoring area.Among them,land desertification area in Linze accounted for 1.7%,in Gaotai for 1.707%,in Sunan for 1.427%,in Jiuquan for 0.851%,in Jiayuguan for 0.276%,in Jinta for 9.391%,in Ejina for 84.648%.It could be seen that the downstream basin of the Heihe River was experiencing the most serious land desertification. Analytical results showed that the causes being responsible for the occurrence and developemt of land desertification in the Heihe River basin include the natual foactors,such as fragile eco-environmnet,high evaporation,arid and windy climate,sparse precipitation and loose surface materials;and irrational human economic activites,such as irrational use of limited water resources etc.,overuse of water resource in the upstream basin leaded to water shortage in the downstram basin,vegetation degradation,overgrazing and thus caused land desertification.