Evaluation of the Priestley-Taylor method to estimate latent heat flux by triangular and trapezoidal approaches using remote sensing data

The current study was carried out to evaluate the Priestley-Taylor (PT) model to estimate latent heat flux (lambda ET) and to compare the performance of the Priestley-Taylor (PT) model by computing PT parameter (phi) by triangular and trapezoidal approaches. The triangular and trapezoidal methods are well established by (e.g., Jiang and Islam, Int J Remote Sens 24:2221-2236, 2003 and Laxmi and Nandagiri, Remote Sens Lett 5:981-990, 2014). Since (Laxmi and Nandagiri, Remote Sens Lett 5:981-990, 2014) trapezoidal approach for estimating latent heat flux is applied and validated only at one flux tower. The present study's novelty is to compute, compare and validate lambda ET in different vegetation types, terrain types. For the validation purpose, lambda ET measurements were collected for diverse vegetation and terrain types where the flux tower was installed. The errors arise due to spatial mismatch between in situ station ground land surface temperature (LST) and MODIS (Moderate Resolution Imaging Spectroradiometer) satellite LST, which is minimal compared to other satellite data products. Relative performances of lambda ET values yielded R-2 of 0.72-0.94 and RMSE of 18.34-32.70 W/m(2) for PT triangular approach. The trapezoidal approach shows good results with high R-2 and low RMSE than the triangular approach. The trapezoidal approach proposed in this study provided reasonably accurate estimates of lambda ET for different types of vegetation and terrain type where the flux towers data available during specific years on AsiaFlux website (https://db.cger.nies.go.jp/asiafluxdb/?page_id=16) were retrieved. As a result of the methods developed in this study, actual evapotranspiration can be derived using XET at regional to spatial scales.