Inter-comparison of the Penman-Monteith type model in modeling the evapotranspiration and its components in an orchard plantation of Southwest China

Abstract

Crop evapotranspiration (ET) along with its components (canopy transpiration (T) and soil evaporation (E)) estimates are crucial for agroecosystem hydrological process research and developing agricultural water-saving strategies. An inter-comparison of the Penman-Monteith type model, including Penman-Monteith (PM), Shuttleworth-Wallace (S-W), Two-Patch (T-P) and topography- and vegetation-based surface energy partitioning algorithm (TVET), Clumping (CL) and developed Two patch-Two layer (T-T) model was conducted to estimate ET and its components in a kiwifruit orchard. Results showed that all models can well capture the pattern of eddy covariance-based hourly ET (ETEC), with a slope of 0.82–1.10, R2 of 0.78–0.83, and RMSE of 0.039–0.049 mm 0.5 h–1, and yield relatively reliable estimates validated by sap flow-based hourly T, with a slope of 0.93–1.16, R2 of 0.72–0.79, and RMSE 0.017–0.026 mm 0.5 h–1. All the P-M type models agreed well with the daily ETEC, with a slope of 0.88–1.21, R2 of 0.82–0.86, and RMSE of 0.55–0.88 mm d–1, respectively. S-W overestimated actual ET due to overestimation in both T and E, T-P and TVET models overestimated T but underestimated actual E as they ignored the soil contribution under the canopy. T-T model outperformed other models in daily ET, T, and E estimates, with R2 of 0.86, 0.73 and 0.73, and RMSE of 0.56, 0.39 and 0.46 mm d–1, respectively. The output ET and T of the different P-M type models were most sensitive to canopy resistance (rsc), while E is most sensitive to aerodynamic resistance between substrate and crop canopy. Net radiation was the most crucial meteorological factor affecting ET, T and E, as it directly participated in the energy balance calculation. The output T was sensitive to air temperature since it affected rsc, while E was relatively sensitive to soil water content since it greatly changed soil surface resistance.