Energy balance simulation of a wheat canopy using the RZ-SHAW (RZWQM-SHAW) model

American Society of Agricultural and Biological Engineers
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Journal Article
American Society of Agricultural and Biological Eng..., 2007, 50 (5), pp. 1507 - 1516
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RZ-SHAW is a new hybrid model coupling the Root Zone Water Quality Model (RZWQM) and the Simultaneous Heat and Water (SHAM model to extend RZWQM applications to conditions of frozen soil and crop residue cover RZ-SHAW offers the comprehensive land management options of RZWQM with the additional capability to simulate diurnal changes in energy balance needed for simulating the near-surface microclimate and leaf temperature. The objective of this study was to evaluate RZ-SHAW for simulations of radiation balance and sensible and latent heat fluxes overplant canopies. Canopy energy balance data were collected at various growing stages of winter wheat in the North China Plain (36 degrees 57'N, 116 degrees 6'E, 28 m above sea level). RZ-SHAW and SHAW simulations using hourly meteorological data were compared with measured net radiation, latent heat flux, sensible heat flux and soil heat flux. RZ-SHAW provided similar goodness-of-prediction statistics as the original SHAW model for all the energy balance components when using observed plant growth input data. The root mean square error (RMSE) for simulated net radiation, latent heat, sensible heat, and soil heat fluxes was 29.7, 30.7, 29.9, and 25.9 W m(-2) for SHAW and 30.6, 32.9, 34.2, and 30.6 W m-2 for RZ-SHAW, respectively. Nash-Sutcliffe R-2 ranged from 0.67 for sensible heat flux to 0.98 for net radiation. Subsequently, an analysis was performed using the plant growth component of RZ-SHAW instead of inputting LAI and plant height. The model simulation results agreed with measured plant height, yield, and LAI very well. As a result, RMSE for the energy balance components were very similar to the original RZ-SHAW simulation, and latent, sensible, and soil heat fluxes were actually simulated slightly better RMSE for simulated net radiation, latent heat, sensible heat, and soil heat fluxes was 31.5, 30.4, 30.2, and 2 7.6 W m(-2). respectively.
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