The Time-Space Variation And Estimation With Remote Sensing Of Evapotranspiration In Ebinur Lake Basin

The study of evapotranspiration is related to a wide range of scientific knowledge, such as hydrology, meteorology, agrology, geography, phytology and so on.It is an important part of matter and energy cycle in the ecological system, and also is one of the important factors of climate change. Because of the lack of water resources in arid and semiarid regions, quantitative calculation of evapotranspiration is necessary for estimating the water demand of agricultural and ecological, planning and reasonable allocating of the water resources and avoiding the waste of water resources. Ebinur lake basin is located in Eurasia hinterland, away from the ocean, lack of the rain. The wind in here is large and windy, the evaporation also is great and sunny. The climate is very dry and there is drastically climate change in Ebinur lake basin. So the climate is a typical temperate continental drought climate. Recently, the increasing of population, expanding of cultivated land area and the developing of social economy in the river basin leaded to the increasing of demand for water, rapidly reduce and cutout of the main rivers water flowing into the Ebinur lake,the declining of underground water level around the lake,the degradation of the lake ecology and ecosystem and also declined the natural vegetation and expaned the desertification.Quantity estimation of evapotranspiration has a great important for comprehensive management and planning of the ecological environment and achievement of sustainable development of river basin. Because of the large area of Ebinur lake basin, the traditional observation and calculation method is not very representative. The remote sensing technology brings a great hope to estimate the evapotranspiration in a large area. This study is based on the SEBAL model, which is more mature and used widely in our country and abroad, and aim to study the daily and monthly characteristics of evapotranspiration on space-time distribution pattern in Ebinur lake basin.This study used the DEM(digital elevation map), MODIS remote sensing products and meteorological stations data in Ebinur lake basin. This study obtained the surface parameters in SEBAL model in view of the slope, aspect, altitude, vegetation height factors, which is based on the MRT, ENVI, ERDAS IMAGE software.In this way the study avoided the faults of traditional calculation methods.The study analyzed the variation trend and period of evapotranspiration in recent 56 year, which was calculated by the Penman-Montieth formula.The conclusion is as follows:(1) The distribution of daily actual evapotranspiration: the actual evapotran spiration of mountains is higher than plain on the spatial distribution, the west ern regions is higher than other places, such as Ala Shan kou and Wen Quan;the daily actual evapotranspiration of mountains is between 4 and 6.90 mm/d,and the deserts is between 0.5 and 2.0 mm/d.On the time distribution, the hig hest evapotranspiration from tell on the whole appeared in July and August. T he average daily actual evapotranspiration of the whole basin is between 4 and6.50 mm/d, and is less than 4.5 mm/d in May, June and September.There we re some differences of actual evapotranspiration from May to September, it als o indicated that the temperature, humidity, sunshine duration and radiation inten sity affect the increase or decline of the evapotranspiration.(2) The distribution of monthly actual evapotranspiration: On the spatial distribution, the actual evapotranspiration of mountains is higher than plain, thegrass is higher than farmland and the farmland is higher than bare land. The lowest actual evapotranspiration appeared in the desert areas. On the timedistribution, the maximum monthly actual evapotranspiration is in July and August and the average value of monthly actual evapotranspiration is between120 and 150 mm / mon, in May, Jun and September it is between 110 and120mm/mon.(3) The time variation of reference crop evapotranspiration: Since the 1960 to 2015, reference crop evapotranspiration has been showed a declining trend in Ebinur lake basin; the mutation of evapotranspiration begined in 1982; In recent 56 years, in the 32 a timescale there are strong periodic in 28 a and weak periodic in 15 a and 8a. The 28 a strong periodic showed that annual evapotrans piration appeared periodicity,such as decline_increase_decline_increase_decli ne. Which can be launched from the above results is that there will be a incre ase of evapotranspiration in the next period.(4) The error between remote sensing inversion results and the reference crop evapotranspiration, eddy covariance observation value was less than 10%, and it is within the scope of permit, so SEBAL model has higher accurac y and reliability for estimating the actual evapotranspiration of Ebinur lake basi n. The observation data was low owing to the large aperture scintillometer, so the LAS observation data was not used to verify the remote sensing inversion results.The low observation data may caused by the improper debugging of th e instrument internal parameters, and may be also related to the surrounding environment of the equipment, such as the topography、the irregularity of unde rlying surface、the temperature of surface soil and moisture of soil layer.These problems need to be explored in future study.