| Gonghe Basin is located in the north eastern part of Qinghai-Tibeten Plateau, belong to arid and semi-arid climate region. Because of the environmental change and population rise, the issue of desertification becomes very serious in Gonghe Basin, Qinghai. In order to maintain the sustainable use of land and water resource, to protect the land from desertification and to make Longyangxia reservoir safe, firstly, the spatially disturbed model has been established in which includes DEM-based precipitation and runoff, regional transpiration and regional water balance modules in Gonghe. Secondly, the model of grassland climate potential productivity and the model of grassland productivity modified by plant water demand and stocking intensity factors has been constructed in Gonghe. According to the carrying capacity and the actual amount of animals on the grassland, coupled with actual grassland investigation, and by using social-economic data, the grassland productivity, species composition, biotope and the cause of desertification has been analyzed. Finally, the evaluation of grassland sustainable use has been performed. The main research results are as follows:1. Annual precipitation series about 50 years is stable and no period; further, the climate drying and desertification aren't caused directly by the decrease of precipitation during the period of the research according to the relational analysis among precipitation temporal-spatial change, runoff, evaporation, potential evapotranspiration and soil water; Longyangxia reservoir which was built in 1986 doesn't have influence on precipitation up to now; but annual temperature series in Gonghe is unstable, having a linear upward trend, and it increases about 0.0247,0.0422 and 0.0272C per year, and temperature rise must be having an influence on desertification, but there is a very little temperature change , so that the effect is very small; annual potential evapotranspiration series is stable too, so climate change has little influence on plant water consumption.2. The runoff has been created in mountain and waters or neighboring regions, and it is 90 percent of the total in rainy season; the total amount of precipitation is 7.08X109m3 in accordance with real amount, about 6.46 X 109m3or so, and it is 9.06 X 109m3in the rainy years, 5.66 X 109m3 in the drying years. There is 3.46 X 109m3 difference between them. So precipitation has a great influence on runoff. Especially, river retreat in drying year becomes one of the main causes of desertification because of the decrease of runoff.3. Temporally, annual potential evapotranspiration is from 882 to 107 lmm, with a mean value of 974mm at Qiabuqia; and it is positively correlational to precipitation and temperature, so it is beneficial for plant growth because precipitation and heat ocurs at the same growth period.; spatially, annual potential evapotranspiration is from 485mm to 1174mm, with a mean value of 1027mm, and it's spatial distribution is negatively correlational to precipitation and slope, whereas positively correlational to temperature and extra solar radiation, therefore the spatio-temporal difference of water become the key factors to plant growth and plant climate potential productivity.The grass evapotranspiration is from 95 to 680mm in space, 494mm on average; and it's total amount is 80.4 X 109 m3, which is 27.6 X 109 m3 higher than annual precipitation; grass evapotranspiration is 9.1 X 109 m3, which is 15.6 X 109 m3 lower than annual precipitation, there is a balance between water demand and supply with annual runoff included in the mountainous area; it is 52.9X 109m3, which is 25.1 X 109m3 less than annual precipitation in the terrace; it is 18.8X 109m3,10.2X109m3 less than annual precipitation in the valley, water becomes a main limiting factors for plant growth..The grass actual evapotranspiration is from 75 to 331mm in space, 255mm on average; and it's total amount is 41.7X 109m3, which is 10.3X 109m3 lower than annual precipitation; it is 7.3X 109m\ which is 15.6X...
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