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ARS Home » Pacific West Area » Boise, Idaho » Northwest Watershed Research Center » Research » Publications at this Location » Publication #187863

Title: Evaluation of SHAW model in simulating the components of net all wave radiation

item Flerchinger, Gerald

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/26/2006
Publication Date: 11/3/2006
Citation: Xiao, W., Flerchinger, G.N., Yu, Q., Zheng, Y. 2006. Evaluation of shaw model in simulating the components of net all wave radiation. Transactions of the ASABE.49(5):1351-1360.

Interpretive Summary: All crop surfaces receive solar radiation from the sun and exchange thermal radiation continuously with the atmosphere. This exchange process is critical to warming and cooling of the plant 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, a detailed model of near-surface heat and water movement, to simulate the surface radiation exchange within a corn canopy was tested using data collected at Yucheng, in the North China Plain. Based on simulation results, the SHAW model can reasonably simulate the surface radiation balance, but weaknesses in the model were identified and point toward areas for future model improvements. Model modifications are planned to address these weaknesses identified in the model. An 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: All surfaces receive short-wave radiation during daylight and exchange long-wave radiation continuously with the atmosphere. This exchange is critical to understanding plant microclimate and ultimately influences plant growth. Simulating radiation exchange accurately will provide agricultural management with a beneficial guide. The Simultaneous Heat and Water (SHAW) model was employed to calculate the components of net radiation (including downward and upward short and long-wave radiation) of a maize canopy using data collected at Yucheng, in the North China Plain. The model simulated upward short- and net all-wave radiation well with model efficiency (ME) equaling 0.97 and 0.98 respectively, while overestimating downward and upward long-wave radiation by 12.1 and 8.3 W m-2 with ME equaling 0.68 and 0.89. Two modifications to the model were implemented and tested to improve the simulated long-wave radiation exchange. In one modification, alternative schemes were tested to simulate cloudy sky long-wave radiation and the best algorithm was employed in the model. With this modification, both downward and upward long-wave radiation was simulated better with ME rising to 0.88 and 0.91. A second modification was implemented to use leaf temperature rather canopy air temperature to compute emitted long-wave radiation, a simplification in the original model. Because upward long-wave radiation was already overpredicted by the original model, this modification made midday simulation even worse as midday leaf temperatures are typically higher than canopy air temperature. This modification did however remove some of the bias in nighttime emitted long-wave radiation. While the SHAW model simulates the radiation balance and transfer processes within the canopy reasonably well, results point to needed areas for model improvement.