Location: Soil and Water Management Research
Title: The Penman-Monteith Equation as a method to initialize canopy temperature in the two-source energy balance model and comparison to other methods Authors
|Agam, Nurit -|
Submitted to: ASA-CSSA-SSSA Annual Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: June 26, 2013
Publication Date: November 3, 2013
Citation: Colaizzi, P.D., Agam, N., Tolk, J.A., Evett, S.R., Howell, T.A., Oshaughnessy, S.A., Gowda, P., Kustas, W.P., Anderson, M.C. 2013. The Penman-Monteith Equation as a method to initialize canopy temperature in the two-source energy balance model and comparison to other methods [abstract]. ASA-CSSA-SSSA Annual Meeting Abstracts. Session 195-10, p.123. Technical Abstract: A two source energy balance (TSEB) model can calculate the energy balance of the soil and canopy separately, which is useful in partitioning evapotranspiration (ET) into the evaporation (E) and transpiration (T) components. One common TSEB formulation is driven by a measurement of surface brightness temperature (Tb). Because Tb commonly includes both canopy (Tc) and soil (Ts) component temperatures for partial canopy cover, the TSEB requires an initial calculation of Tc, and then solves the energy balance by iteration. The initial calculation of Tc commonly uses the Priestley-Taylor (PT) equation, which has resulted in reasonable agreement between calculated and measured ET for most ranges of vapor pressure deficit. However, in recent studies where separate measurements of E and T were obtained, the PT equation overestimated initial Tc, resulting in incorrect partitioning of soil and canopy fluxes, where E and T were over- and under-estimated, respectively. Substitution of the Penman-Monteith (PM) equation, where the bulk canopy resistance term was allowed to vary during iteration, greatly reduced error in E and T calculations compared with the PT equation, especially when vapor pressure deficit exceeded 3.5 kPa. The recursive combination method (RCM) is a version of the PM equation where Tc is allowed to vary in calculating the saturated vapor pressure-temperature relation, but the more complex RCM did not reduce error between calculated and measured E, T, and ET compared with the PM. Comparison of the PT, PM, and RCM methods used in the TSEB will be discussed in light of the physical assumptions of each method.