The estimation of regional daily total evapotranspiration based on layered bowen ratio and its validation

First the paper discussed the importance of daily total evapotranspiration in hydrology, agriculture, forestry and environmental studies. Then the function relation between evaporative fraction and Bowen ratio was discussed based on energy balance without advection. Variation of Bowen ratio with time front China Ecosystem Research Network was classified into four types and the influential factors were analyzed. And daily total evapotranspiration was estimated based on the flux observations of the stations. The results showed that average error of about twelve percent was probably produced without considering variation of Bowen ratio with nine when retrieving daily total evapotranspiration. Finally the paper retrieved total evapotranspiration of North China Plain in DOY78, 2002 based on the hypothesis that Bowen ratio was unchanged in a day, a two-layer model and,MODIS data in combination with the weather data. The results showed that it is necessary to take variation of Bowen ratio with time into account to further improve the retrieval precision of daily total evapotranspiration based on remote sensing.

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