Latent Heat Flux and Canopy Conductance Based on Penman-Monteith, Priestley-Taylor Equation, and Bouchet's Complementary Hypothesis

A novel method is presented to analytically resolve the terrestrial latent heat flux (lambda E) and conductances (boundary layer g(B) and surface g(S)) using net radiation (R-N), ground heat flux (G), air temperature (T-a), and relative humidity (RH). This method consists of set of equations where the two unknown internal state variables (g(B) and g(S)) were expressed in terms of the known core variables, combining diffusion equations, the Penman-Monteith equation, the Priestley-Taylor equation, and Bouchet's complementary hypothesis. Estimated lambda E is validated with the independent eddy covariance lambda E observations over Soil Moisture Experiment 2002 (SMEX-02); the Global Energy and Water Cycle Experiment (GEWEX) Continental-Scale International Project (GCIP) selected sites from FLUXNET and tropics eddy flux, representing four climate zones (tropics, subtropics, temperate, and cold); and multiple biomes. The authors find a RMSE of 23.8-54.6 W m(-2) for hourly lambda E over SMEX-02 and GCIP and 23.8-29.0 W m(-2) for monthly lambda E over the FLUXNET and tropics. Observational and modeled evidence in the reduction in annual evaporation (E) pattern on the order of 33% from 1999 to 2006 was found in central Amazonia. Retrieved g(S) responded to vapor pressure deficit, measured lambda E, and gross photosynthesis in a theoretically robust behavior. However, the current scheme [Penman-Monteith-Bouchet-Lhomme (PMBL)] showed some overestimation of lambda E in limited soil moisture regimes. PMBL provides similar results when compared with another Priestley-Taylor-based lambda E estimation approach [Priestley-Taylor-Jet Propulsion Laboratory (PT-JPL)] but with the advantage of having the conductances analytically recovered.