A novel method of retrieving potential ET in China

Abstract

Terrestrial evaporation is the central link of land surface energy balance, which is very important for climate change, water cycle research and drought monitoring. Potential evapotranspiration (ETP) is an important form of ET, which play a significance for calculating standardized precipitation evapotranspiration index (SPEI). This paper proposed a novel method of retrieving ETP using precipitable water vapor (PWV) and temperature to obtain the high precision and resolution ETP dataset, and the ETP and SPEI are obtained with the temporal-spatial resolutions of monthly and 0.125° × 0.125°, respectively, in China. The PWV derived from the European Center for Medium-range Weather Forecasts (ECMWF) is first validated and calibrated using the Global Navigation Satellite System (GNSS) technique. ETP and SPEI at specific stations are then calculated using the site-based revised Thornthwaith (S-RTH) model with high precision. Finally, spherical harmonic function is applied to fit the coefficients of the S-RTH model in China, and a RTH model over China (C-RTH) with high spatial resolution (0.125° × 0.125°) is established. Statistical result reveals that (1) the average root mean square (RMS) and mean absolute error (MAE) of the calibrated ECMWF-derived PWV have been improved from 2.0/1.7 mm to 1.7/1.4 mm, respectively using the GNSS-derived PWV. (2) The improvement rate of ETP derived from the S-RTH model is approximately 68% compared with that from the TH model, and the average RMS and MAE of the ETP difference between S-RTH and Penman–Monteith (PM) are 10.7 mm and 8.5 mm, respectively. (3) The average RMS and MAE of potential difference between C-RTH and PM are 17.6 mm and 13.7 mm, respectively. Although the accuracy of the C-RTH model is slightly lower than that of the S-RTH model, it is significantly improved compared with the TH model, and the calculated ETP data have been converted from point to surface. The proposed method expands the application of GNSS technique to obtain ETP data set, which provides the basic data guarantee for drought disaster prevention and control in China.