Estimation of land surface evapotranspiration over the Heihe River basin based on the revised three-temperature model

Evaporation and heat transfer mechanisms differ for different types of soils. In this study, Evapotranspiration (ET) models for the bare soil, vegetation land, and the mixed regions were developed based on the Land Surface Energy Balance Theory. Surface energy fluxes and daily ET of the Heihe River Basin were estimated using Moderate Resolution Imaging Spectroradiometer (MODIS) satellite data and meteorological observation data, including the daily duration time of the sun, air temperature, etc. based on the revised three-temperature model (3T model), and then the distribution maps of ET were retrieved. Thereafter, Evaporator pan (E-601) measurements obtained from meteorological observation stations in the study area were chosen to validate the accuracy of the calculated ET. Results showed that the maximum absolute error was 1.70 mm/d, whereas the minimum was 0.05 mm/d, which indicated that the revised 3T model was of adequate accuracy in estimating ET in the study area and could be extended to the regional scale. Also, the spatial distribution of surface ET was different in the upper, middle and lower reaches in the study area and fit with vegetation conditions. On the whole, the ET increased from desert of northeast to mountain of southwest. The results showed that the ET in the study area ranged from 0.06 to 7.00 mm/d, with an average value of 2.43 mm/d, on 2 August 2008. The highest ET values was from the forest or alpine meadow areas in the upper reaches, with more than 4 mm/d, the lowest values was from the Gobi desert in the lower reaches, with below 2 mm/d, and ET of oasis in the middle reaches was not only changed with the crop growth stage and vegetation conditions, but also controlled greatly by human activities, with more than 3.5 mm/d. Copyright (c) 2011 John Wiley & Sons, Ltd.