Global Evapotranspiration Datasets Assessment Using Water Balance in South America

Abstract

Evapotranspiration (ET) connects the land to the atmosphere, linking water, energy, and carbon cycles. ET is an essential climate variable with a fundamental importance, and accurate assessments of the spatiotemporal trends and variability in ET are needed from regional to continental scales. This study compared eight global actual ET datasets (ETgl) and the average actual ET ensemble (ETens) based on remote sensing, climate reanalysis, land-surface, and biophysical models to ET computed from basin-scale water balance (ETwb) in South America on monthly time scale. The 50 small-to-large basins covered major rivers and different biomes and climate types. We also examined the magnitude, seasonality, and interannual variability of ET, comparing ETgl and ETens with ETwb. Global ET datasets were evaluated between 2003 and 2014 from the following datasets: Breathing Earth System Simulator (BESS), ECMWF Reanalysis 5 (ERA5), Global Land Data Assimilation System (GLDAS), Global Land Evaporation Amsterdam Model (GLEAM), MOD16, Penman–Monteith–Leuning (PML), Operational Simplified Surface Energy Balance (SSEBop) and Terra Climate. By using ETwb as a basis for comparison, correlation coefficients ranged from 0.45 (SSEBop) to 0.60 (ETens), and RMSE ranged from 35.6 (ETens) to 40.5 mm·month−1 (MOD16). Overall, ETgl estimates ranged from 0 to 150 mm·month−1 in most basins in South America, while ETwb estimates showed maximum rates up to 250 mm·month−1. ETgl varied by hydroclimatic regions: (i) basins located in humid climates with low seasonality in precipitation, including the Amazon, Uruguay, and South Atlantic basins, yielded weak correlation coefficients between monthly ETgl and ETwb, and (ii) tropical and semiarid basins (areas where precipitation demonstrates a strong seasonality, as in the São Francisco, Northeast Atlantic, Paraná/Paraguay, and Tocantins basins) yielded moderate-to-strong correlation coefficients. An assessment of the interannual variability demonstrated a disagreement between ETgl and ETwb in the humid tropics (in the Amazon), with ETgl showing a wide range of interannual variability. However, in tropical, subtropical, and semiarid climates, including the Tocantins, São Francisco, Paraná, Paraguay, Uruguay, and Atlantic basins (Northeast, East, and South), we found a stronger agreement between ETgl and ETwb for interannual variability. Assessing ET datasets enables the understanding of land–atmosphere exchanges in South America, to improvement of ET estimation and monitoring for water management.

Evapotranspiration Assessment by Remote Sensing in Brazil with Focus on Amazon Biome: Scientometric Analysis and Perspectives for Applications in Agro-Environmental Studies

“…Analyzing data from the Amazon basin, they found MOD16 and P-LSH performed better than other methods, such as ERA5 and CMIP models, despite all underestimating actual evapotranspiration. Ruhoff et al [39] also used the water balance residual method to estimate evapotranspiration in South America and Rodell et al [93] applied the water balance residual method to estimate evapotranspiration in seven river basins in different locations around the world, including the Tocantins-Araguaia basin in Brazil. This highlights the potential challenges of using water balance methods, particularly due to uncertainties in surface runoff measurements.…”

“…Focusing on remote sensing studies for large-scale ET evaluation, we reviewed seven articles for South America [24,37,39,[44][45][46][47], four for Brazil [25,[48][49][50], and seven at the regional level. For regional studies, three assessed the Northeast region [10,51,52], one covered both the Southeast and Northeast regions [53], another focused on the Bauru mesoregion in São Paulo [54], and one each dealt with transition zones between the Cerrado and Amazon (Cerrado/Amazônia and Urucuia Aquifer) [55][56][57].…”

“…Studies have been conducted at global [21,22] and continental levels [23,24], within specific biomes [25][26][27], individual states [28,29], river basins of varying sizes [30][31][32], small experimental units [33,34], and even focusing on specific Landsat scenes [35,36]. This heterogeneity in scale and modeling approaches has prompted numerous comparisons of ET estimation methods, both with each other and against in situ data [7,[37][38][39], seeking to identify the most accurate and effective techniques.…”

Validation and Comparison of Seven Land Surface Evapotranspiration Products in the Haihe River Basin, China

“…In situ measurements, including the Bowen ratio, lysimeters, laser isotopes, and eddy co-variance, can be used as the relative true values in pixel-scale evaluations to evaluate ET products. Regional evaluations are based on the water balance method [17][18][19][20][21] and the multi-site scale expansion method [22]. In the absence of ground truth ET data, indirect validation becomes feasible, which includes the cross-checking method, multi-scale evaluation method based on high-resolution remote sensing data, and spatiotemporal change trend analysis method.…”