A Penman-Monteith evapotranspiration model with bulk surface conductance derived from remotely sensed spatial contextual information

Abstract

A novel approach involving the use of the contextual information in a scatter plot of Moderate Resolution Imaging Spectrometer (MODIS) derived Land Surface Temperature versus Fraction of Vegetation (LST vs. F<inf>v</inf>) has been proposed in this study to obtain pixel-wise values of bulk surface conductance (G<inf>s</inf>) for use in the Penman-Monteith (PM) model for latent heat flux (?<inf>ET</inf>) estimation. Using a general expression for G<inf>s</inf> derived by assuming a two-source total ?<inf>ET</inf> (canopy transpiration plus soil evaporation) approach proposed by previous researchers, minimum and maximum values of G<inf>s</inf> for a given region can be inferred from a trapezoidal scatter plot of pixel-wise values of LST and corresponding F<inf>v</inf>. Using these as limiting values, G<inf>s</inf> values for each pixel can be derived through interpolation and subsequently used with the PM model to estimate ?<inf>ET</inf> for each pixel. The proposed methodology was implemented in 5 km × 5 km areas surrounding each of four flux towers located in tropical south-east Asia. Using climate data from the tower and derived G<inf>s</inf> values the PM model was used to obtain pixel-wise instantaneous ?<inf>ET</inf> values on six selected dates/times at each tower. Excellent comparisons were obtained between tower measured ?<inf>ET</inf> and those estimated by the proposed approach for all four flux tower locations (R2 = 0.85–0.96; RMSE = 18.27–33.79 W m–2). Since the LST- F<inf>v</inf> trapezoidal method is simple, calibration-free and easy to implement, the proposed methodology has the potential to provide accurate estimates of regional evapotranspiration with minimal data inputs. © 2019, © 2019 Informa UK Limited, trading as Taylor & Francis Group.