Kim et al. (2026) A structural correction to atmospheric evaporative demand narrows the gap between offline aridity diagnostics and Earth system model projections

Identification

• Journal: npj Climate and Atmospheric Science
• Year: 2026
• Date: 2026-01-05
• Authors: Daeha Kim, Minha Choi
• DOI: 10.1038/s41612-025-01306-3

Research Groups

• Department of Civil Engineering, Jeonbuk National University, Republic of Korea
• School of Civil, Architectural Engineering & Landscape Architecture, Sungkyunkwan University, Republic of Korea
• Department of Global Smart City, Sungkyunkwan University, Republic of Korea

Short Summary

This study demonstrates that the divergence between offline aridity diagnostics and Earth system model (ESM) projections is primarily due to structural inconsistencies, specifically the violation of precipitation-potential evapotranspiration independence caused by land-atmosphere feedbacks. A thermodynamic correction using the complementary evaporation principle significantly reduces this bias, bringing offline evapotranspiration trends closer to ESM projections.

Objective

• To demonstrate that the divergence between offline aridity diagnostics and Earth system model (ESM) projections stems from structural inconsistencies in offline frameworks, specifically the violation of the assumption that potential evapotranspiration (PET) and precipitation (P) are independent climatic constraints, and to show how a thermodynamic correction can narrow this gap.

Study Configuration

• Spatial Scale: Global land surfaces, analyzed on a pixel-by-pixel basis at 0.25°×0.25° (ERA5) and 1°×1° (CMIP6) resolutions.
• Temporal Scale: Historical period (1981–2020) and future projections (2015–2100, specifically 2071–2100 for late-century analysis) using monthly and annual aggregated data.

Methodology and Data

• Models used:
  • Penman equation (open-water, PETOW)
  • Two-source Penman–Monteith formulation (vegetated, PETVeg)
  • Complementary Evaporation Principle (CEP) framework (for WETOW, WETVeg)
  • Budyko framework (Turc–Mezentsev equation)
  • Coupled Model Intercomparison Project Phase 6 (CMIP6) Earth System Models
• Data sources:
  • ERA5 reanalysis (precipitation, actual evapotranspiration, 2 m air and dew-point temperatures, surface net radiation, 2 m wind speed, LAI)
  • CMIP6 ESMs (historical: 1980–2014; SSP5-8.5: 2015–2100)
  • Gridded atmospheric carbon dioxide concentration ([CO2]) datasets (Cheng et al., 2022)

Main Results

• Conventional PET estimates (PETOW, PETVeg) exhibit strong negative correlations with precipitation (P–PET correlations of −0.45 ± 0.29 and −0.34 ± 0.29, respectively), violating the Budyko framework's independence assumption.
• Applying the Complementary Evaporation Principle (CEP) deflation significantly reduces these correlations towards near zero (−0.14 ± 0.42 for WETOW, −0.02 ± 0.42 for WETVeg).
• CEP deflation substantially reduces the inflation of the aridity index (Φ) and brings offline diagnostic evapotranspiration (ET) trends closer to ESM projections under the SSP5-8.5 scenario.
• Under the SSP5-8.5 scenario by 2100, the uncorrected PETOW yields an ET trend of +0.61 mm yr⁻², which is more than double the ESM ensemble mean of +0.28 mm yr⁻².
• Combining both CEP deflation and physiological suppression (WETVeg) reduces the Budyko-derived ET trend to +0.39 mm yr⁻², significantly narrowing the gap with ESM projections.
• The study concludes that structural inconsistencies, rather than missing physiological processes alone, play a central role in the mismatch between offline diagnostics and ESM hydrology.

Contributions

• Identifies that the violation of the P-PET independence assumption due to land-atmosphere feedbacks is a more fundamental cause of divergence between offline aridity diagnostics and ESMs than previously emphasized factors (e.g., missing physiological effects, sub-annual variability).
• Introduces and demonstrates the effectiveness of the Complementary Evaporation Principle (CEP) as a thermodynamic structural correction to PET, significantly improving the agreement between offline Budyko-type models and ESM projections.
• Quantifies the relative contributions of structural inconsistencies versus process-based deficiencies in the mismatch, showing that structural corrections are essential for theoretically valid offline hydrologic assessments.

Funding

• National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (RS-2024-00416443)

Citation

@article{Kim2026structural,
  author = {Kim, Daeha and Choi, Minha},
  title = {A structural correction to atmospheric evaporative demand narrows the gap between offline aridity diagnostics and Earth system model projections},
  journal = {npj Climate and Atmospheric Science},
  year = {2026},
  doi = {10.1038/s41612-025-01306-3},
  url = {https://doi.org/10.1038/s41612-025-01306-3}
}