Estimation of hourly actual evapotranspiration over the Tibetan Plateau by random forest model

Actual evapotranspiration (ETa) is a key variable in the energy and water cycle of the earth climate system. Evapotranspiration product with high temporal resolution and accuracy is of great significance to the effective use of water resources and regulation of local climate. Here, one–year hourly ETa over the entire Tibetan Plateau (TP) was estimated by a combination use of satellite data from Fengyun-4A and Random Forest (RF) model. The validation against in situ measurements from six stations equipped with eddy-covariance instruments shows a root mean square error (RMSE) of 32.24 mm month^-1 and a correlation coefficient of 0.85. Compared with results from surface energy balance system (SEBS) with a RMSE value of 59.13 mm month^-1, Maximum Entropy Production (MEP) with a RMSE value of 62.28 mm month^-1 and the European Centre for Medium-Range Weather Forecasts Reanalysis-5 (ERA5) with a RMSE value of 53.64 mm month^-1, the ETa results from RF model have the highest accuracy. The annual spatial average RF ETa over the whole TP was about 387.34 mm. Thus, the total ETa of the TP was about 1039.85 km³ yr⁻¹. The annual average ETa in the eastern (long. > 95°E), central (95°E ≥ long. > 85°E) and western (long. ≤ 85°E) parts of the TP are 478.63 mm, 356.94 mm and 279.67 mm, respectively. In addition, diurnal averaged and monthly averaged ETa over different land cover types and different climate zones over the TP were also clearly identified. The ETa over cropland and the humid area is the highest with the largest variation range.