Submitted to: Environmental and Water Resources Institute World Congress Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 8/28/2005
Publication Date: 5/15/2005
Citation: Colaizzi, P.D., Evett, S.R., Howell, T.A., Tolk, J.A. 2005. Lysimetric evaluation of single- and two-source energy balance models for alfalfa, grain sorghum, and cotton in the Southern High Plains. In: Proceedings of the American Society of Civil Engineers-Environmental and Water Resources Institute, World Water and Environmental Resources Congress, May 15-19, 2005, Anchorage, Alaska. p. 1-13. Interpretive Summary: Estimating water use of agricultural crops and other vegetation has numerous applications in meteorology, ground and surface water hydrology, crop science, and on-farm irrigation management. Water use of vegetated surfaces can be estimated using surface temperature and standard meteorological data. Surface temperature can be remotely sensed by thermal infrared thermometers from the ground or aboard aircraft or satellites. The surface temperature reported by infrared thermometers is a mixture of vegetation and soil, which complicates estimates of water use and evaporation. We evaluated two types of models that use surface temperature to estimate crop water use. The first type considers the surface as homogenous and does not attempt to account for differences in soil and vegetation temperature (termed the “single source”), whereas the second type does (termed the “two-source” because soil and vegetation are modeled as separate sources). We found that crop water use estimates were more accurate using the two-source energy balance model. This is an important finding because although the two-source is computationally more intensive than the single source model, it does not require additional input data beyond that required by the single source model.
Technical Abstract: The performance of a single source energy balance (SSEB) model was compared to a two source energy balance model described by Norman et al. (1995) and Kustas and Norman (1999), which has formulations using parallel and series resistances in the soil-canopy-atmosphere continuum (TSEB-pr and TSEB-sr, respectively). Sensible (H) and latent (LE) heat fluxes predicted by each model were compared to H and LE derived from precision weighing lysimeters for several seasons of fully irrigated alfalfa, dryland grain sorghum, and deficit irrigated cotton in Bushland, TX, USA. Each model requires surface temperatures, which were provided by infrared thermometers that viewed the lysimeter surface. Although the TSEB-sr requires additional assumptions in computing the resistance in the canopy boundary layer and some approximations in solving the resulting non-linear system of equations, its predictions of H and LE were better than those predicted with the SSEB or the TSEB-pr for all crops, which represented a variety of surface roughness and height characteristics. This implied that energy exchange between the soil and canopy could be significant, and this is considered by resistances in series. All models tended to underestimate the magnitude of H, which led to LE being overestimated, especially during periods of regional advection that commonly occurs at the study location.