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United States Department of Agriculture

Agricultural Research Service

Research Project: ENHANCED SYSTEM MODELS AND DECISION SUPPORT TOOLS TO OPTIMIZE WATER LIMITED AGRICULTURE

Location: Agricultural Systems Research Unit

Title: Simulating the surface energy balance in a soybean canopy with SHAW and RZ-SHAW models

Authors
item MA, LIWANG
item FLERCHINGER, GERALD
item AHUJA, LAJPAT
item SAUER, THOMAS
item PRUEGER, JOHN
item MALONE, ROBERT
item HATFIELD, JERRY

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 21, 2011
Publication Date: February 5, 2012
Citation: Ma, L., Flerchinger, G.N., Ahuja, L.R., Sauer, T.J., Prueger, J.H., Malone, R.W., Hatfield, J.L. 2012. Simulating the surface energy balance in a soybean canopy with SHAW and RZ-SHAW models. Transactions of the ASABE. 55(1):175-179.

Interpretive Summary: Correct simulation of surface energy balance in a crop canopy is critical for better understanding of soil water balance, canopy and soil temperature, plant water stress, and plant growth. One existing effort is to incorporate the surface energy balance in the Simultaneous Heat And Water (SHAW) into the Root Zone Water Quality Model (RZWQM). In this study, an improved version of RZ-SHAW hybrid model was tested for a soybean canopy for energy balance components (net radiation, sensible heat, latent heat, and ground heat flux), canopy and soil temperature, evapotranspiration (ET), and soil water content against measured data and against predictions of the original SHAW model. In terms of root mean squared error (RMSE), Both RZ-SHAW and SHAW simulated net radiation, sensible heat, and latent heat well. However, the ground heat flux simulated by RZ-SHAW was slightly worse with RMSE of 28.9 W m-2 compared to 22.6 W m-2 for SHAW, which could be due to difference in evaporation simulations. Simulated soil temperature at both 1.5 cm and 4.5 cm by RZ-SHAW was comparable to that of SHAW with RMSE of 2.18 oC and 2.23 oC, respectively, compared to 2.13 oC and 2.20 oC by SHAW. Similarly, simulated canopy temperature was essentially the same with RMSE of 1.77 oC by RZ-SHAW and 1.69 oC by SHAW. Simulated surface soil water was reasonable for both models. Simulated ET had a RMSE of 0.069 cm d-1 by RZ-SHAW and 0.074 cm d-1 by SHAW. However, we had to increase the minimum soil water suction for plant water uptake from 1500 kPa to 3500 kPa to meet transpiration demand during dry soil conditions. The evaluated RZ-SHAW can be used as a new tool to better simulate soil-crop water conditions by providing complete energy balance and canopy temperature.

Technical Abstract: Correct simulation of surface energy balance in a crop canopy is critical for better understanding of soil water balance, canopy and soil temperature, plant water stress, and plant growth. One existing effort is to incorporate the surface energy balance in the Simultaneous Heat And Water (SHAW) into the Root Zone Water Quality Model (RZWQM). In this study, an improved version of RZ-SHAW hybrid model was tested for a soybean canopy for energy balance components (net radiation, sensible heat, latent heat, and ground heat flux), canopy and soil temperature, evapotranspiration (ET), and soil water content against measured data and against predictions of the original SHAW model. In terms of root mean squared error (RMSE), both RZ-SHAW and SHAW simulated net radiation, sensible heat, and latent heat well. However, the ground heat flux simulated by RZ-SHAW was slightly worse with RMSE of 28.9 W m-2 compared to 22.6 W m-2 for SHAW, which could be due to difference in evaporation simulations. Simulated soil temperature at both 1.5 cm and 4.5 cm by RZ-SHAW was comparable to that of SHAW with RMSE of 2.18 oC and 2.23 oC, respectively, compared to 2.13 oC and 2.20 oC by SHAW. Similarly, simulated canopy temperature was essentially the same with RMSE of 1.77 oC by RZ-SHAW and 1.69 oC by SHAW. Simulated surface soil water was reasonable for both models. Simulated ET had a RMSE of 0.069 cm d-1 by RZ-SHAW and 0.074 cm d-1 by SHAW. However, we had to increase the minimum soil water suction for plant water uptake from 1500 kPa to 3500 kPa to meet transpiration demand during dry soil conditions. The evaluated RZ-SHAW can be used as a new tool to better simulate soil-crop water conditions by providing complete energy balance and canopy temperature.

Last Modified: 8/19/2014