ET-WB: water-balance-based estimations of terrestrial evaporation over global land and major global basins

Abstract

Abstract. Evaporation (ET) is one of the crucial components of the water cycle, which serves as the nexus between global water, energy, and carbon cycles. Accurate quantification of ET is, therefore, pivotal in understanding various earth system processes and subsequent societal applications. The prevailing approaches for ET retrievals are either limited in spatiotemporal coverage or largely influenced by the choice of input data or simplified model physics, or a combination thereof. Here, using an independent mass conservation approach, we develop water-balance-based ET datasets (ET-WB) for the global land and the selected 168 major river basins. We generate 4669 probabilistic unique combinations of the ET-WB leveraging multi-source datasets (23 precipitation, 29 runoff, and 7 storage change datasets) from satellite products, in situ measurements, reanalysis, and hydrological simulations. We compare our results with the four auxiliary global ET datasets and previous regional studies, followed by a rigorous discussion of the uncertainties, their possible sources, and potential ways to constrain them. The seasonal cycle of global ET-WB possesses a unimodal distribution with the highest (median value: 65.61 mm per month) and lowest (median value: 36.11 mm per month) values in July and January, respectively, with the spread range of roughly ±10 mm per month from different subsets of the ensemble. Auxiliary ET products illustrate similar intra-annual characteristics with some over- or underestimation, which are completely within the range of the ET-WB ensemble. We found a gradual increase in global ET-WB from 2003 to 2010 and a subsequent decrease during 2010–2015, followed by a sharper reduction in the remaining years primarily attributed to the varying precipitation. Multiple statistical metrics show reasonably good accuracy of monthly ET-WB (e.g., a relative bias of ±20 %) in most river basins, which ameliorates at annual scales. The long-term mean annual ET-WB varies within 500–600 mm yr−1 and is consistent with the four auxiliary ET products (543–569 mm yr−1). Observed trend estimates, though regionally divergent, are evidence of the increasing ET in a warming climate. The current dataset will likely be useful for several scientific assessments centering around water resources management to benefit society at large. The dataset is publicly available in various formats (NetCDF, Mat, and Shapefile) at https://doi.org/10.5281/zenodo.8339655 (Xiong et al., 2023).

Response of evapotranspiration to the 2022 unprecedented extreme drought in the Yangtze River Basin

“…This method is commonly employed as the reference to evaluate ET products over the basin scale (Long et al, 2014; Xu et al, 2019). Monthly water balance‐derived ET (WBET) can be generated using three hydrological components: precipitation, runoff and TWS, expressed as follows (Rodell, Famiglietti, et al, 2004; Xiong et al, 2023): where P is monthly precipitation (mm), R is monthly runoff (mm) and is monthly changes in TWS (mm). Here, refers to the difference between TWS at the start and end of the month t .…”

“…The first method is based on the monthly GRACE‐mascon data and calculate by differencing the TWS in preceding and following months and then dividing by 2 months, which is a common operation combined with the backward difference and smoothing approach. Previous studies often have approximated the using the similar operation (Long et al, 2014; Xiong et al, 2023). The second method is to apply the daily TWS from the assimilation product proposed by Li et al (2019).…”

“…This method is commonly employed as the reference to evaluate ET products over the basin scale (Long et al, 2014;Xu et al, 2019). Monthly water balance-derived ET (WBET) can be generated using three hydrological components: precipitation, runoff and TWS, expressed as follows (Rodell, Famiglietti, et al, 2004;Xiong et al, 2023):…”