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United States Department of Agriculture

Agricultural Research Service

Title: Simulating Surface Energy Fluxes and Radiometric Temperatures for Two Arid Vegetation Communities Using the Shaw Model

Authors
item Flerchinger, Gerald
item Kustas, William
item Weltz, Mark

Submitted to: Journal of Applied Meteorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 8, 1997
Publication Date: N/A

Interpretive Summary: Accurately predicting transfer of water and energy at the soil atmosphere interface is crucial to understanding of surface/atmosphere interactions, improving atmospheric circulation models used to analyze global change scenarios, and improving hydrologic models of water supply and plant interactions. These applications require extrapolation of energy and water rpredictions to large land areas, making coupling with remotely sensed surface temperature and soil moisture available from satellites a necessity. The Simultaneous Heat and Water (SHAW) model is a detailed physical process model capable of simulating the effects of a multi-species plant canopy on heat and water transfer at the soil-atmosphere interface. The model was used to simulate the surface energy balance and surface temperature of two vegetation communities using data collected on the Walnut Gulch Experimental Watershed. The two vegetation communities included a grass-dominated and a shrub-dominated site. Variation in heat and water transfer at the soil surface, transpiration of water from the plants, and plant and soil surface temperatures were simulated quite well for both sites. The potential for verifying and periodically updating model predictions of surface energy and water transfer using satellite observations were explored. Further development of this technology can provide accurate predictions of plant water use, soil moisture, and heat and energy transfer for application in atmospheric circulation and hydrologic models.

Technical Abstract: Soil-Vegetation-Atmosphere-Transfer (SVAT) models are gaining attention as the need to better represent the interaction between the soil and atmosphere in atmospheric circulation models becomes more apparent. The Simultaneous Heat and Water (SHAW) model is a detailed physical process model capable of simulating the effects of a multi-species plant canopy on heat and water transfer at the soil-atmosphere interface. The model was used to simulate the surface energy balance and surface temperature of two vegetation communities using data collected during the Monsoon '90 multidisciplinary field experiment. The two diverse vegetation communities included a sparse, relatively homogeneous, grass-dominated community and a shrub-dominated site with large bare interspace areas between shrubs. The diurnal variation in the surface energy balance was simulated well at both sites, while canopy leaf temperatures were simulated somewhat better at the erelatively homogeneous grass-dominated site. The variation in surface fluxes accounted for by the model (i.e. model efficiency) ranged from 65% and 59% for latent heat flux at the grass-dominated and shrub-dominated site, respectively, to 98% for net radiation at both sites. Canopy leaf temperatures for the shrub-dominated site were consistently overpredicted by 1.8oC compared to measured values. Soil surface temperature were simulated quite well at both sites (mean bias error less than 0.9oC and model efficiency of 94%). The ability of the model to simulate canopy and surface temperature gives it the potential to be verified and periodically updated using satellite observations of radiometric surface temperature when extrapolating model-derived fluxes to other areas.

Last Modified: 12/21/2014
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