ARS | Publication request: EVALUATION OF A TWO-SOURCE ENERGY BALANCE MODEL IN AN ADVECTIVE ENVIRONMENT

Submitted to: Proceedings of the World Water and Environmental Resources Congress
Publication Type: Proceedings
Publication Acceptance Date: February 15, 2006
Publication Date: May 20, 2006
Citation: Colaizzi, P.D., Evett, S.R., Howell, T.A., Tolk, J.A., Li, F. 2006. Evaluation of a two-source energy balance model in an advective environment. In: Proceedings of the World Water and Environmental Resources Congress. Examining the Confluence of Environmental and Water Concerns, May 21-25, 2006, Omaha, Nebraska. 2006 CDROM.

Interpretive Summary: Crop water use (termed evapotranspiration, or ET) can be estimated from thermal infrared measurements of surface temperature, meteorological data, and mathematical models. Since surface temperature is a mixture of vegetation and soil temperatures, mathematical models must separate these temperatures in order to accurately estimate total ET. We tested a model for estimating ET using infrared surface temperatures for alfalfa, corn, cotton, grain sorghum, winter wheat, wheat stubble, and bare soil in the windy environment of the Texas Panhandle. The model tended to overestimate ET of crops and surfaces when ET was low (such as when the soil was dry and the crop was sparse), but usually provided accurate estimates of ET when it was high (such as for windy conditions, hot days, and fully grown crops). These results are important because they show that the model is feasible for estimating ET for a number of crops and surfaces in the harsh environment of the US Southern Great Plains; furthermore, the model should continue to be refined to improve its accuracy. Accurate models for estimating regional ET will facilitate water conservation in irrigated agriculture.

Technical Abstract: A two-source energy balance model (TSEB) was evaluated in terms of latent heat flux (LE) for six crops, wheat stubble, and bare soil in an advective environment, and net radiation (Rn) was modeled both with and without separate transfer characteristics used for visible and near-infrared radiation. Observed (i.e., ground-truth) LE was derived from changes in mass measured by precision weighing lysimeters averaged to 0.5-h, and observed Rn was measured by net radiometers at the lysimeters. Agreement between observed and predicted Rn was not greatly influenced by separation of visible and near-infrared radiation, possibly because constant soil albedo was assumed for visible and near-infrared wavelengths. The TSEB tended to overestimate LE for lower observed LE (< |400| W m-2) by up to 200 W m-2, but relative error improved as observed LE increased and appeared not to be influenced by strong regional advection.