Abstract
Offline aridity and drought diagnostics typically project widespread terrestrial drying under climate change, whereas fully coupled Earth system models (ESMs) often simulate modest or regionally heterogeneous changes—and in some regions increasing—runoff. This long-standing divergence has been attributed largely to missing vegetation physiological effects and the neglect of sub-annual climate variability in offline diagnostic frameworks. Here, we show that a more fundamental issue is the violation of the diagnostic framework’s structural requirement that potential evapotranspiration (PET) and precipitation (P) act as independent climatic constraints. Using Penman and Penman–Monteith formulations, each with and without thermodynamic deflation via the complementary evaporation principle (CEP), we demonstrate that land–atmosphere feedbacks embedded in conventional PET estimates induce strong negative P–PET correlations (−0.45 ± 0.29; mean ± standard deviation) across land surfaces, which collapse toward near zero (−0.02 ± 0.42) after CEP deflation. Preserving PET–P independence substantially reduces inflation of the aridity index and brings offline diagnostic ET trends closer to ESM projections under a strong-emission scenario (from +0.61 to +0.39 mm yr−2; ESM mean: +0.28 mm yr−2). These results indicate that structural inconsistencies—rather than missing physiological processes alone—play a central role in the mismatch between offline diagnostics and ESM hydrology. Ensuring that PET is not inflated by land–atmosphere feedbacks is therefore essential for theoretically valid offline hydrologic assessments under a warming climate.
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Data availability
The ERA5 reanalysis and CMIP6 datasets used to reproduce the results of this study are publicly available from the Copernicus Climate Data Store (https://cds.climate.copernicus.eu/) and the IPSL ESGF node (https://esgf-node.ipsl.upmc.fr/projects/cmip6-ipsl/), respectively. The downscaled [CO2] dataset is accessible at Zenodo (https://zenodo.org/records/5021361).
Code availability
Python scripts used to estimate PET from meteorological inputs and to apply the CEP deflation are available upon reasonable requests from the first author (daeha.kim@jbnu.ac.kr).
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Acknowledgements
This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (RS-2024-00416443).
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D.K. conceived the study, performed the calculations, generated the visualizations, drafted the manuscript, and led the interpretation and discussion of the results. M.C. contributed to the discussion, interpretation, and revision of the manuscript. All authors reviewed and approved the final manuscript.
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Kim, D., Choi, M. A structural correction to atmospheric evaporative demand narrows the gap between offline aridity diagnostics and Earth system model projections. npj Clim Atmos Sci (2026). https://doi.org/10.1038/s41612-025-01306-3
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DOI: https://doi.org/10.1038/s41612-025-01306-3
