A Two-Source Model for Estimating Evaporative Fraction (TMEF) Coupling Priestley-Taylor Formula and Two-Stage Trapezoid

Abstract

Remotely sensed land surface temperature and fractional vegetation coverage (LST/FVC) space has been widely used in modeling and partitioning land surface evaporative fraction (EF) which is important in managing water resources. However, most of such models are based on conventional trapezoid and simply determine the wet edge as air temperature (T a ) or the lowest LST value in an image. We develop a new Two-source Model for estimating EF (TMEF) based on a two-stage trapezoid coupling with an extension of the Priestly-Taylor formula. Latent heat flux on the wet edge is calculated with the Priestly-Taylor formula, whereas that on the dry edge is set to 0. The wet and dry edges are then determined by solving radiation budget and energy balance equations. The model was evaluated by comparing with other two models that based on conventional trapezoid (i.e., the Two-source Trapezoid Model for Evapotranspiration (TTME) and a One-source Trapezoid model for EF (OTEF)) in how well they simulate and partition EF using MODIS products and field observations from HiWATER-MUSOEXE in 2012. Results show that the TMEF outperforms the other two models, where EF mean absolute relative deviations are 9.57% (TMEF), 15.03% (TTME), and 30.49% (OTEF).

Comparison of Three Theoretical Methods for Determining Dry and Wet Edges of the LST/FVC Space: Revisit of Method Physics

“…Furthermore, we compared the three theoretical methods for estimating LE by determining the dry and wet edges in a Two-source Model for estimating Evaporative Fraction (TMEF) [19]. The LE was estimated based on the same TMEF model and the same input parameters but with different boundaries of the LST/FVC space.…”

“…Since the vegetation under each site is maize, a maximum possible LAI of 5.0 was selected in the Moran method [32]. FVC was calculated from NDVI using a non-linear relationship, i.e., FVC = [(NDVI − NDVI min )/(NDVI max − NDVI min )] 2 where NDVI min and NDVI max were set as 0.2 and 0.86 [19].…”

“…Diagram of the dry and wet edges in Land surface temperature and fractional vegetation coverage (LST/FVC) space [19].…”

Intercomparison of Three Two-Source Energy Balance Models for Partitioning Evaporation and Transpiration in Semiarid Climates

“…The iterative procedure is commonly adopted in the TSEB model and this approach is verified by different researchers [69,74,75]. The VFC/LST-based approach and related contextual-based method are applied by different researchers, such as Zhang et al [24], Zhang et al [55], Merlin et al [44], Merlin et al [45], Long and Singh [47], Yang et al [48], Song et al [53], and Sun [49].…”

“…The main assumption of this method is that the isolines in the VFC/LST trapezoid space is mainly controlled by soil water availability and the isolines within a VI/LST trapezoidal space are used to decompose the composite temperature into component temperatures. This method was recently revised and adopted by Sun et al [46], Long and Singh [47], Yang and Shang [48], Yang et al [25], and Sun [49] to develop two-source models.…”