The characteristics of water resources and the changes of the hydrological process and environment in the arid zone of northwest China

Water resources in the arid zones of northwest China mainly come from mountain areas and then flow to and disappear in the piedmont plains. These water resources, with inland river basins as the geographic unit, form relatively independent ecosystems and the surface runoff flowing out of the mountain mouth becomes the only water source available for the middle and lower reaches of these basins. Both the ecosystem stability and sustainable development depend on the surface water and groundwater resources of these inland river basins. Over the last 50 years, exploitation of water and land resources in the arid northwest regions of China has been expanding, forming 390.07 X 10(4) ha of irrigation eases, with construction of 622 reservoirs of different sizes with a total storage capacity of 65.5 X 10(8) m(3) ensuring the sustainable development of industrial and agricultural production. In the meantime it has also caused a series of environmental changes. Discharge of the majority of rivers has been drastically reduced (even dried up), river courses have been shortened, and terminal lakes contracted or dried up. Land desertification and soil salinization has developed rapidly. Vegetation is degrading and biodiversity is decreasing, as compared with the early 1950s; the natural grassland area is decreasing by 16-75.4%. Economical and high-effective use of water resources and harmonization of eco-environment benefits with economic benefits are the fundamental ways to achieve sustainable development of arid northwest China.