Modeling Evapotranspiration and Energy Balance in a Wheat-Maize Cropping System Using the Revised RZ-SHAW Model.

Abstract: Correctly simulating evaoptranspiration (ET) and surface energy balance is essential to estimating crop growth under water and heat stress conditions in agricultural systems. The revised hybrid model (RZ-SHAW), combining the Root Zone Water Quality Model (RZWQM) and Simultaneous Heat and Water (SHAW) model, was evaluated for estimating ET and surface energy balance components against observed data from an eddy covariance system in a wheat-maize double cropping system. The simulated soil water and crop growth agreed well with observed data after an automatic parameter optimization. The daily ET was slightly under-estimated by 0.05 mm in wheat seasons and over-estimated by 0.34 mm in maize seasons, compared with the observed from latent heat flux (LE) across 2003 to 2005. The root mean squared error (RMSE) and model efficiency (ME) values were 0.55 mm and 0.81 for the three years. The revised model estimated plant transpiration reasonably during middle and late crop seasons with RMSE and ME values of 0.56 mm and 0.78. The observed and estimated seasonal actual ET or potential ET showed a strong linear relation with slope value of near one. The goodness of fit for LE, H (sensible heat flux) and canopy temperature was better in the middle crop seasons than in the early crop seasons. The RMSE values for estimated Rn (net radiation), H , LE, G (ground heat flux) , and canopy temperature were 33.6, 36.8, 42.0, 30.2 W m-2, and 1.37 oC, respectively, for middle wheat seasons and were 28.7, 35.0, 44.9, 21.6 W m-2, and 1.22 oC, respectively, for middle maize seasons. These simulation results were comparable with previous studies, indicating that the revised hybrid model is reasonable for estimating ET, surface energy balance as well as crop growth under various climate and seasons.