Uncertain effect of component differences on land evapotranspiration

Abstract

Study region: Global and 28 large river basins Study focus: Actual evapotranspiration (ETa) plays a key role in the redistribution of water, carbon and energy. The emergence of many ETa products has made uncertainty assessment increasingly important. The FLUXNET2015 dataset and 28 large watershed water balance datasets were used in this study. The monthly scale products of the ERA5-Land reanalysis data (ERA5), Global Land Data Assimilation System (GLDAS), Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA) and Penman-Monteith-Leuning Model Version 2 (PML) terrestrial evapotranspiration models were evaluated from 2001 to 2017. The differences in composition (vegetation transpiration (T), soil evaporation (Es), canopy interception loss (Ei) and other components (open water and ice and snow sublimation) (Eo)) and vegetation among the four ETa products were compared.New Hydrological Insights for the Region: At the site scale, the ERA5 and MERRA products significantly outperformed the GLDAS and PML products, with the latter exhibiting poorer reliability in site validation. The PML product's basin-scale water balance KGE metric overall outperformed those of the ERA5, GLDAS, and MERRA products, with KGE > 0 in 23 basins. The use of basin-scale data mitigates the impact of local outliers on the simulation results, leading to KGE validation metrics at the basin scale that are overall superior to those obtained from site-scale validation. There were large errors in the estimates of T and Es in the ERA5 product, related to the overestimation of Es and underestimation of T. The boundary between sea and land (used to divide marine evapotranspiration and land evapotranspiration) was unclear in the PML products. Eo/ETa was overestimated, and there were clearly high values at the land margin (Eo peaks as high as 3803 mm/yr). The difference in evapotranspiration components had a considerable influence on the uncertainty of ETa. The vegetation types in the 4 ETa products for DBF***, EBF***, ENF***, MF***, GRA***, and CRO*** all exhibited significant differences at the P<0.001 level. This study contributes to product uncertainty analysis and the determination of ways to improve ETa products.

Keywords

• Land evapotranspiration
• Component differences
• Uncertainty
• Evapotranspiration components