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Energy budget of Amazonian forests has a large influence on regional and global climate, but relevant data are scarce. A novel energy partition method based on the maximum entropy production (MEP) theory is applied to simulate evapotranspiration in Amazonia. Using site‐level eddy flux data, the MEP method shows high skill at the hourly, daily, and monthly scales. Consistent performance under different levels of land surface dryness is revealed, hinting that drought signal is appropriately resolved. The site‐level MEP‐based estimates outperform the estimates of the Moderate Resolution Imaging Spectroradiometer evapotranspiration product, which is commonly used for large‐scale assessments. At the Amazon basin scale, the two series yield similar averages but exhibit spatial differences. The parameter parsimony and demonstrated skill of the MEP method make it an attractive approach for environments with diverse strategies of water flux control. Classical methods for estimating vapor flow from vegetated surfaces, known as the process of evapotranspiration, require input data on water vapor gradient, wind speed, and surface roughness as well as model parameters that are often difficult to obtain from in situ and remote sensing observations. The uncertainty of these variables can be especially large for the Amazon rainforest with high biodiversity, making it challenging to evaluate evapotranspiration in space and time. In this study, we assess the performance of a novel model that needs fewer input data and model parameters than classical methods. The model performance is validated through comparison with observations from nine sites across the Amazon basin and shows a better skill as compared to a commonly used evapotranspiration product. We also show that the model has a satisfactory performance in estimating evapotranspiration when satellite data are used, providing reasonable estimates at the scale of the entire Amazon basin. Maximum entropy production theory demonstrates excellent skill in estimating evapotranspiration (ET) in the Amazon rainforestModel performance is consistent at different drought levels without using surface resistance parametersLarge differences are found with a commonly used ET product based on Moderate Resolution Imaging Spectroradiometer data

The 21st century evapotranspiration (ET) trends over the continental U.S. are assessed using innovative, energy‐based principles. Annual ET is projected to increase with high confidence at the rate of 20 mm for every 1℃ of rise in near‐surface air temperature, or 0.45 or 0.98 mm/year/year, depending on the emission scenario. The ET trajectory is dominated (58%) by the increase of land‐surface net radiative energy. An enhancement of the fraction of energy taken up by ET becomes a more important controller (53%) in late 21st century, under the high emission scenario. This increase is explained by the “tug of war” between atmospheric vapor demand and land‐surface ability to supply water. An assessment of future water availability (precipitation minus ET) shows no significant changes at the continental scale. This outcome nevertheless hides strong spatial variability, emphasizing the role of ET in shaping the distribution of water availability among human populations. Water quantity in the environment is strongly controlled by its evaporation into the atmosphere from plants, soil, and water bodies—the process that is called evapotranspiration. This study calculates evapotranspiration trend over the U.S. during the 21st century and assesses factors determining its evolution. Annual evapotranspiration is predicted to grow at the rate of 20 mm for every 1° Celsius of rise in near‐surface air temperature, leading to 14%–23% increase with respect to the historic period, depending on climate scenario. This increase is due to the impacts of future greenhouse gas emissions on energy that fuels evapotranspiration, as well as interplay between the growing water vapor demand by the atmosphere and changing land‐surface water supply conditions in the warmer climate. The predicted evapotranspiration trends will result in the strengthening of uneven distribution of water quantity across the U.S. in the future. Maximum Entropy Projection theory yields robust estimates of evapotranspiration (ET) under a warmer climateAvailable energy surplus and supply‐demand interactions result in temporally linear increase of ET over the contiguous U.SET and precipitation changes result in uneven spatial distribution of water availability (precipitation minus ET) Maximum Entropy Projection theory yields robust estimates of evapotranspiration (ET) under a warmer climate Available energy surplus and supply‐demand interactions result in temporally linear increase of ET over the contiguous U.S ET and precipitation changes result in uneven spatial distribution of water availability (precipitation minus ET)