| Shiyang River Basin is located in the Arid Region of Northwest China. Water resources of this region are very limiting. With the development of economy and increase of population, much ecological demand of water was used by industry and agriculture. Water resources shortage had caused a series of environmental problems. Such as soil erosion, vegetation degradation land desertification. The problem of water resources is sharp in this basin. The research of ecological water requirement is foundation to determine the optimum combination of vegetation structure and ecological potential degradation area in Shiyang River Basin. And the research has some reference value to ecological environment protection and restoration. It also has important reference value to allocate water resources and carry out sustainable management of water resources.The simulation of the surface flux and the evapotranspiration were calculated using the technology of Remote Sensing and SEBAL model, combining the basic data such as meteorologieal data, MODIS image and terrain data. The rule of temporal and spatial distribution of evapotranspiration and the relation with surface parameters were analyzed. On this basin, ecological water requirement of Shiyang River was calculated using evapotranspiration method. Then the distribution of ecological water requirement and water supply path was analyzed. The recommendations of the ecological construction in Shiyang River Basin were put forward. This research has some reference value to ecological environment protection and restoration. The main content and conclusion is:(1) This study used SEBAL model and remote image MODIS to estimate the evapotranspiration in Shiyang River Basin. Spatial distribution and characters of evapotranspiration at different period were analyzed. The results showed that evapotranspiration has obvious distribution rule in Shiyang River. Evapotranspiration is largest in Upper reaches region. There is a decreasing trend from upstream to downstream. And evapotranspiration has very clear regional boundaries between different types of land. Evapotranspiration in vegetation coverage region is significantly greater than in bare areas and desert areas. Evapotranspiration reached 5mm in summer in upper region. But it is fluctuant from lmm to 2.5mm in desert areas and only 0.5mm in some region in spring and winter.(2) This study used landsat TM image to estimate the land use data in Shiyang River Basin. And present situation of land use was analyzed. The results showed that ecosystem is very fragile in Shiyang River Basin. Desertification area and unused land reached half of the land of this basin. Agricultural land has become a major land use types. Grass also has a larger coverage area. But the low coverage grassland is half of the total area of grassland covering. The total coverage area of all forest land accounted for only 6.55% of the whole basin, far less than the average forest coverage in China.(3) The results showed that farmland,forest and grassland are main ecological use land in Shiyang River Basin. The evapotranspiration of farmland,forest,high coverage grassland,middle coverage grassland and lower coverage grassland were 632.74 mm,787.27 mm,749.21 mm,704.24 mm and 580.80mm respectively in vegetation growing period in 2004. The order of month evapotranspiration is same during different period in a year. And the distribution was a double peak curve.(4) Ecological water requirement of every type land was calculated using evapotranspiration method. The results showed that ecological water requirement is 133.26x 108m3 in vegetation growing period in 2004. Farmland water requirement is largest and reached 44.60 x 108m3. The water requirement of forest,high coverage grassland,middle coverage grassland and lower coverage grassland were20.33×108m3,12.56×108m3,23.20×108m3,32.57×108m3 respectively in 2004.(5) By further analysing for ecological water consumption and source, and the vegetation distribution and the type of ecological water consumption, the development policy based on protecting nature plant of Shiyang River Basin and Minqin oasis was proposed. Upstream and midstream of Shiyang River Basin should develop shrub and middle coverage grassland. It is not suitable to pursuit Arbor and high coverage grassland.Minqin oasis should develop natural vegetation along the river. It is not recommended in some region with low ground water level to plant artificial tree and grass. The key to maintain Minqin oasis is to maintain a certain river flow and reduce the exploitation of groundwater. The measure will make groundwater level gradually restore and natural vegetation gradually recover. This is the fundamental way to improve the ecological environment in Shiyang River basin. |
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