Estimating basin evapotranspiration using distributed hydrologic model

Proposed in this study is an approach to estimate regional evapotranspiration from potential evaporation using a distributed hydrologic model. If water is freely available in the storage tank of interest, evapotranspiration is taken as Penman's potential evaporation. Otherwise, the reduction of actual evapotranspiration from potential evaporation is estimated using the simplified Philip's soil-moisture relationship with the combination of a physically based distributed tank (PDTank) model. The average annual evapotranspiration in the study area is estimated to be 716 mm. Results are also compared with the actual evapotranspiration estimated by using Morton's complementary relationships areal evapotranspiration (CRAE) model and Brusaert-Stricker's advection-aridity (AA) model. These three models give quite similar performance of goodness. The AA model gives the largest estimation for the annual evapotranspiration, the physically based distributed tank (PDTank) model gives the smallest estimation, and the CRAE model shows the amount in-between the AA model and the PDTank result. But the PDTank gives better results than both the CRAE and the AA models for winter evapotranspiration.