LAUSR

Abstract Reliable estimation of actual evapotranspiration (AET) is essential for hydrological, ecological, and land-surface models. The water balance method is a useful tool for estimating AET. However, it usually neglects soil moisture (SM), which is a dominant factor in AET simulation. Based on field observations, an inverse hydrological modeling method was proposed for regional AET simulation. The method can be applied to estimate AET in other basins, where observations of SM are available. A nonlinear relationship between AET and potential evapotranspiration, a soil water constraint factor, was developed and calibrated for the studied basin. Results of the AET evaluation indicated this relationship was able to estimate AET accurately for both monthly and two-week series, as the Nash and Sutcliffe efficiency coefficient (NSE) was 0.903 and 0.613, respectively. The meteorologically based complementary relationship (CR) method was also able to estimate monthly AET accurately, in particular the revised CR method. But it showed poor performance when estimating AET at a shorter timescale. The performance of the revised CR method with a calibrated parameter was better than that of the initial CR method, as the NSE improved from 0.52 to 0.70. Overall, the performance of the nonlinear relationship with calibrated parameters was better than that of the CR method. In conclusion, monthly AET can be accurately estimated using the CR method based only on meteorological data.