Research On Ecological Variation Of Vegetation And The Influencing Factors In Yinchuan Plain Based On Remote Sensing Data

Located in arid and semi-arid area, Ningxia is one of the areas with weakest ecological environment. The weak eco-environment restricts the economic and social development of Ningxia province. From 2002 onwards, the water allocation of Ningxia area has been decreased in order to solve the problem of water inception for Yellow River. The shortage of water resources made the eco-environment become worse and induced the composition of main environmental factors incompatible. The natural function of eco-system became low, the environmental capacity became little and the ecological balance is weak.On the basis of summarizing many national and international references, this research studied the variation of ecological vegetation from 1982 to 2002 in Ningxia area by using GIMMS NDVI and MODIS NDVI which was issued by NASA. According to the result, from 1982 to 1999, the development of vegetation in most areas was good except Yanchi-Mahuangshan area. However, after 2000, with the decrease of water allocation of the Yellow River, the vegetation of Yinchuan plain, Zhongning plain and Hongsipu area began recession in small extent. Based on the analysis of meteorological data, the vegetation in Yanchi-Mahuangshan area, Helan mountain area and Liupan mountain area are influenced by precipitation. The recession of vegetation in Hongsipu area was the effect of secondary salinization which was induced by human activity.With area of 7,790 km~2, Yinchuan plain is located in north area of Ningxia province and has a very important position in social and economic development. In this paper, the principle of vegetation recession in this area was discussed in detail. According to the result, the ecological vegetation in Yinchuan plain was influenced by water allocation of the Yellow River. The main reason of the recession was the descending of the groundwater level which was induced by decreasing of water allocation from the Yellow River.The relationship between groundwater level and vegetation development wasalso discussed in this paper. The proper water level for the development of vegetation is 3 m and the interval is 2m to 4m. It would induce soil sanilization if the water depth is lower than 2m and the groundwater supply is less for vegetation if the water depth is more than 4m.At last, the ecological water demand of Yinchuan oasis was calculated in this paper. The smallest ecological water demand is 49.56 X 108m3 if the vegetation could developed normally and there is no recession trend in vegetation. The influence of the water depth for evapotranspiration is very small if the water depth is more than 3 m after the simulation of the relationship between ground water depth and evapotranspiration.