Comparison of an improved Penman-Monteith model and SWH model for estimating evapotranspiration in a meadow wetland in a semiarid region

Accurately estimating evapotranspiration (ET) for meadow wetland ecosystems is of great significance for water management in semiarid regions. Taking a meadow wetland ecosystem in the Horqin Sandy Land as an example, this study coupled the Ball-Berry canopy stomatal conductance model to Penman-Monteith (P-M) model and Shuttleworth-Wallace (S-W) model, and the improved P-M model and SWH model were calibrated and validated by long-term (2013–2018 growing seasons) eddy covariance (EC) measurements. The results indicated that the improved P-M model and SWH model performed well either at half-hourly or daily timescales, with high coefficient of determination (R2) and index of agreement (IA) and low root mean square error (RMSE). Generally, the SWH model performed better than the improved P-M model, especially under the low leaf area index (LAI) conditions. In addition, in the growing seasons from 2013 to 2018, the mean ET measured by the EC system was 2.78 mm/d, which was approximately equal to the mean modeled ET from the SWH model (2.75 mm/d) and slightly higher than the mean modeled ET from the improved P-M model (2.34 mm/d). The improved P-M model and SWH model were highly sensitive to the parameter in estimating canopy surface resistance and to vapor pressure deficit (VPD) in meteorological variables.