Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/2007
Publication Date: 8/1/2007
Citation: Yu, Q., Flerchinger, G.N., Xu, S., Kozak, J.A., Ma, L., Ahuja, L.R. 2007. Energy balance simulation of a wheat canopy using the rz-shaw (rzwqm-shaw) model. Trans. of ASABE 50(5): 1507-1516.
Interpretive Summary: The Root Zone Water Quality Model (RZWQM) is a powerful research and management tool for simulating crop growth, nutrient processes and water quality impacts, however its ability to track over-winter conditions were limited. A hybrid model coupling RZWQM and the Simultaneous Heat and Water (SHAW) model, termed RZ-SHAW, was developed to improve soil temperature simulation and over-winter snow and frozen soil effects within the model. The study evaluated the RZ-SHAW by comparing model simulations of heat, water and crop growth components with field measurements. The results demonstrated a successful coupling of RZWQM and SHAW in terms of canopy energy balance simulation. RZ-SHAW is offered as a new comprehensive model for simulating management and climate effects on crop development, nutrient cycling, runoff and water quality. Emergence and development of crops, their pests, and various soil organisms are altered by heat and water movement near the soil-atmosphere interface. The ability to accurately simulate heat, water and nutrient movement at the surface and within the soil can enhance land management.
Technical Abstract: RZ-SHAW is a new hybrid model coupling the Root Zone Water Quality Model (RZWQM) and the Simultaneous Heat and Water (SHAW) Model to extend RZWQM applications to conditions of frozen soil and soil surface with crop residue cover. The objective of this study was to evaluate RZ-SHAW for simulations of radiation balance and sensible and latent heat fluxes over plant canopies. Canopy energy balance data were collected at various growing stages of winter wheat in the North China Plain (36'57'N, 116'36'E, 28 m above see level). Both RZ-SHAW and SHAW were compared for net radiation, latent heat fluxes, sensible heat fluxes, and soil heat fluxes using hourly meteorological data. RZ-SHAW provided essentially the same goodness-of-prediction as the original SHAW model for all the energy balance components when using observed plant growth input data. The average root mean square error (RMSE) for simulated net radiation, latent heat, sensible heat, and soil heat was 31.3 W m-2 for SHAW and 35.8 W m-2 for RZ-SHAW. The slight differences between the two models might be attributed to different methods of soil water balance calculation. An analysis was performed using the plant growth component of RZ-SHAW instead of inputting LAI, plant height, and initial water content. The model simulation results agreed with the plant height and yield very well. However, predicted leaf area index (LAI) and water contents during results deviated from measured values. As a result, the average RMSE for the energy balance components was slightly higher (41.7 W m-2) than the other two model simulations. However, when LAI was in good agreement with measured LAI, the simulated energy balance components did match the measured values very well. Overall, the results demonstrated a successful coupling of RZWQM and SHAW in terms of canopy energy balance simulation. RZ-SHAW offers a new model to simulate diurnal changes in energy balance and air temperature needed for simulating plant canopy effects on soil temperature