Evaluation of Six Land Surface Evapotranspiration Products over the Tibetan Plateau

Uncertainties in the evapotranspiration (ET) products used in the Tibetan Plateau (TP) region were determined based on the data from satellite remote sensing and observations having different spatial and temporal resolutions, limiting their utility for hydrometeorological and climate assessment. Six ET (PML, EB-ET_V2, GLEAM, GLDAS, ERA5_Land, and MOD16) products were evaluated based on eddy observations, and the differences between the products were compared. Moreover, the uncertainties in ET products in the TP region were analyzed. The results of the analysis are as follows: (1) A good correlation and consistency exist in the mean state and seasonal cycle between the observed and ET values of the corresponding pixel. Moreover, GLEAM product exhibits a high degree of agreement with the observed values and has applicability, and MOD16 product exhibits poor performance at most sites. (2) In terms of seasonal changes, ERA5_Land product values are highly consistent with the observed changes during spring, GLEAM product values are nearly consistent with the observed changes during summer and winter, and EB-ET_V2 product values are highly consistent with observed values during autumn. (3) Spatially, GLEAM product has higher correlation (the correlation coefficient R＞0.88) and consistency (index of agreement IOA＞0.89) compared to those of EB-ET_V2 product and GLDAS product. Substantial differences exist in the temporal and spatial distribution of various products during different seasons, especially during spring. Compared with other products, MOD16 product is underestimated in summer and overestimated in winter in most regions. (4) The annual average ET for each product except for MOD16 product is considerably different. The annual average ET values of the remaining five products over multiple years arranged in descending order are as follows: ERA5_Land product (401.46 mm a⁻¹)＞PML product (334.37 mm a⁻¹)＞GLEAM product (298.46 mm a⁻¹)＞EB-ET_V2 product (271.39 mm a⁻¹)＞GLDAS product (249.67 mm a⁻¹). The total annual evaporation in the TP region is 330.59 mm a⁻¹. The assessment results provide a detailed understanding of the quality and dynamics of ET products in the TP region, which can serve as reference data for regional water management and water resource assessment in the TP region.