Submitted to: Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 4/1/2008
Publication Date: 4/19/2008
Citation: Flerchinger, G.N., Xiao, W., Sauer, T., Yu, Q. 2008. Evaluation of the SHAW Model for Within-Canopy Radiation Exchange. 35 pp. On compact-disk, International Symposium on Crop Modeling and Decision Support Systems, Jiangsu Key Laboratory for Information Agriculture, Nanjing Agricultural University, Nanjing China.
Interpretive Summary: The exchange of solar and thermal radiation is critical to warming and cooling of plant canopies and ultimately influences plant growth. Understanding these transfer processes within the soil-plant-atmosphere system enhances our ability to predict plant response and to evaluate management and climate scenarios. The ability of the Simultaneous Heat and Water (SHAW) model to simulate the surface radiation exchange within wheat, corn, and soybean canopies was tested. Based on simulation results, the SHAW model can reasonably simulate the surface radiation balance, but weaknesses in the model for simulating within canopy radiation exchange were identified. Modifications to the model were implemented to improve model simulations. The improved model will lead to a more reliable model for evaluation of management and climate scenario influences on plant microclimate and plant response.
Technical Abstract: Radiation exchange at the surface plays a critical role in the surface energy balance, plant microclimate, and plant growth. The ability to simulate the surface energy balance and the microclimate within the plant canopy is contingent upon simulation of the surface radiation exchange. A validation and modification exercise was conducted of the Simultaneous Heat and Water (SHAW) model for simulating the surface radiation exchange over and within wheat, maize and soybean plant canopies using data collected at Yucheng, in the North China Plain and near Ames, Iowa. Methodologies were developed for simulating short-wave and long-wave radiation fluxes within a multi-species, multiple layer plant canopy. Although the original SHAW model slightly underpredicted reflected solar radiation, one would conclude that the simulations were quite reasonable if within-canopy measurements were not available. However, within canopy short-wave radiation was seriously underestimated by the original SHAW model. Improvements were made to the SHAW model for simulating radiation exchange within the plant canopy. Modification to the SHAW model improved both above canopy reflected radiation and within-canopy radiation simulations. Alternative approaches to simulating canopy transmissivity to diffuse radiation had a minor influence on simulated short-wave radiation, but made almost no difference in simulated long-wave radiation or evapotranspiration.