Consistency and uncertainty of gridded terrestrial evapotranspiration estimations over China

Terrestrial evapotranspiration (ET) is a critical process in water, energy and carbon cycles but challenging to estimate. Several gridded terrestrial ET products have been developed for regional or global applications based on different algorithms and forcing inputs and with different temporal-spatial resolutions and accuracy. This study systematically investigates the consistency and uncertainty of eight ET products over China for the period from 2003 to 2014. Temporal and spatial pairwise correlation analysis indicates that the ET products are largely consistent with each other, among which the ET estimates from GLEAM and EB-ET presenting highest spatial consistency with each other (R-2 = 0.91). Compared to the ground-based observations from the flux network, the centered root-mean-squared-deviation (RMSD) for each of the eight products is found lower than 30 mm/month, according to which CR and PMLv2 outperform the others. The ET products however show considerable difference in the estimated mean annual ET averaged over China (from 378 mm/a to 528 mm/a). Uncertainty assessment based on the extended collocation method (ECM) suggests the uncertainties in ET estimates are more evident in the arid region than in the humid region. It also indicates that model averaging (like that in generating the GLASS ET product) could substantially reduce the uncertainties. The findings of this research could facilitate the application of the ET products to assess water balance dynamics over China while considering their uncertainties.