Estimation of evapotranspiration over Wuding River Basin with an eco-hydrological model and MODIS data
基于MODIS数据的无定河流域蒸散模拟

A physically distributed eco-hydrological model(VIP model),under support of Terra-MODIS remotely sensed vegetation index,land use and DEM data,is applied to simulate the temporal and spatial variation of evapotranspiration and other water balance components over the Wuding River Basin on the Loess Plateau,from 2000 to 2003.The spatial resolution of the simulation is 250 m and time step of 1 hour.The results show that the mean evapotranspiration is 300 mm,397 mm,460 mm and 443 mm in 2000,2001,2002 and 2003,respectively;the annual evapotranspiration amount is the main component of water budget and the evaporation value from soil is a bit larger than the canopy transpiration;evapotranspiration over the basin mainly occurred during summer time,which contributes more than 60% of the annual amount;and the annual values of evapotranspiration from the vegetation types are similar,though their monthly processes are quite different.This is the common phenomenon in the semi-arid region.Over the whole basin,the annual amount of evapotranspiration and its components are decreasing gradually from the southeastern part to the northwestern part of the basin;the coefficient of variation of evaporation and transpiration is 30% and 14% respectively,whereas that of evapotranspiration is only 9%,due to the compensating effect of evaporation and transpiration.The simulated annual evapotranspiration values over the nine sub-basins of the Wuding River Basin agree well with the evapotranspiration derived from water balance method,showing that the simulation results of VIP model are reasonable.The result from this study is valuable for assessing water conservation projects and serves as reference for re-vegetation policy making.