Estimation Of Evapotranspiration In Heihe River Basin Based On Remote Sensing

Land surface energy flux is an important part in global water cycle and energy balance. The research on land surface energy flux is very important in global climate change, land surface atmosphere interaction, as well as in water resources management. Moreover, water is the source of life. More over, water is the fudamental guarantee of human survival, socio-economic development and sustainable development. With the increasing population and rapid development of economy, water shortage has become a restrictive factor to the development of many areas around the world. The water resource has become a hot issue in the 21st century. Evapotranspiration is an important part in water cycle. Thoroughly understanding of regional evapotranspiration condition is extremely important for water resources plan and water resources management. Under the situation of water shortage and deteriorating water quality, in order to utilize the water resources efficient, it is very important to realize regional evapotranspiration.The traditional site observation is only valid in small spatial size. In recent years, with the rapid development of remote sensing technology as well as quantitative inversion method, regional evapotranspiration detection based on remote sensing has become a hot research field. This method can effectively avoid the defect exists in traditional methods. It has great value for water resources planning and management in regional scale.Heihe River Basin is the second largest inland river basin in northwest of China arid region. Sustainable use of water resources related to ecological, environmental, econo-mic and other important areas. Therefore, there is an urgent need for acknowledge basin water balance in its spatial distribution and temporal changes with scientific and quantitative understanding.Thus, the research to the evapotranspiration mechanism, the spatial distribution and temporal changes of evapotranspiration in the Heihe River Basin, is extremely urgent. In order to afford some reference to watershed management, we need a clear understanding of the evapotranspiration process in the Heihe River Basin. In this paper, MODIS data and field observation data were collected. Based on the theory of quantitative remote sensing, vegetation index, leaf area index, surface emissivity, and other important surface parameters were retrived. Using time series analysis method, some important vegetation phenological information, such as the beginning of season, end of season, length of season, NDVI amplitude of season, were extracted. Based on SEBS model, using the surface parameters as input, evapotranspiration of typical days in the Heihe River Basin were calculated. The time scale expansion methods were systematic summarized. Using the METRIC method proposed by Allen as the time scale exapansion method, evapotranspiration in each month of 2008 were calculated.The main research results are as follows: 1.Phenological information is a good indicator of vegetation status. With the sixteen-day maximum value composite (MVC) MODIS dataset, the phonological information was extracted using the Savitzky-Golay filter. The spatial characteristics of the beginning of season, the end of season, the length of season, NDVI amplitude of season were analyzed. The result showed that phonological information in the Heihe River Basin have obvious spatial pattern. The upstream mountainous grass have a short grow season, the middlestream areas were affected by intense human activities, phonological information is consistent with crops of wheat, maize growth state.2.Deeply understanding of evapotranspiration mechanism, temporal and spatial distribution of evapotranspiration in Heihe River Basin is extremely important for durative use of water resources and watershed management. Based on SEBS model, evapotranspiration of typical days in the Heihe River Basin were calculated. Moreover, the results were verified with flux data of Yinke station. The results are nice except the result in the day of 121 st and 151 st.3.The spatial distribution of monthly evapotranspiration, annual evapotranspira-tion have more practical value in irrigation, water resources management. With the review of time scale expansion methods, the METRIC method which proposed by Allen was selected. Then, evapotranspiration in each month of 2008 were calculated.