Research On Evaporation And The Influencing Factors In Yinchuan Plain Based On Remote Sensing

Located in arid and semi-arid area, with strong evapotranspiration (ET) and little precipitation, the eco-environment of the Yinchuan plain is very fragile and the groundwater is very important for the human living and social development. Accurately calculation of the groundwater evaporation is not only important for the evaluation and development of the groundwater resources, but also crucial for understanding the interchange among groundwater, surface water and atmospheric water. Therefore, research on the groundwater evaporation and its influence factors can provide scientific reference for development and evaluation of the shallow groundwater resources, reasonable allocation of the plain water resources and eco-environment protection. Based on the Surface Energy Balance System, this thesis studied ET in Yinchuan Plain from January 2004 to December 2004 using NOAA/AVHRR which was issued by NASA. The result indicated that, the ET first increase to maximum in July and then reduce in October, The ET in north part of the plain is larger than that of the south part in dry season and on the contrary, the ET in north part is less than that of the south part in high water period. This paper also estimate the smallest ecological water demand in the Yinchuan Plain. The smallest ecological water demand is 45.82×108m~3 if the vegetation could developed normally and there is no recession trend in vegetation.This paper also study the influence of the temperature、precipitation、groundwater depth and NDVI for ET in Yinchuan Plain. The relationship between temperature, precipitation and ET presents positive correlation. The influence of the groundwater depth for ET is very small if the groundwater in more than 3m after the simulation of the relationship between water depth and ET in lower water period. On the other hand, the threshold depth of evaporation of the phreatic water is 5m. If the groundwater depth is larger than 5m, there is no evaporation of phreatic water and it is only occurred evaporation of soil evaporation. The NDVI also affects the ET significantly. The daily ET of the no-vegetation area (NDVI<0.2) is almost the same as that of the vegetation area (NDVI>0.2) if the groundwater depth is above 1m. The daily ET of the vegetation area is larger than that of no-vegetation area when the groundwater depth is between 1m and 5m, and the difference ET between vegetation area and no-vegetation area is the transpiration. The daily ET is close to be a constant and it represents the evaporation of the soil water if the groundwater depth is more than 5m.