Zhong et al. (2025) Sub-diurnal asymmetric warming has amplified atmospheric dryness since the 1980s

Identification

• Journal: Nature Communications
• Year: 2025
• Date: 2025-09-09
• Authors: Ziqian Zhong, Hans W. Chen, Aiguo Dai, Tianjun Zhou, Bin He, Bo Su
• DOI: 10.1038/s41467-025-63672-z

Research Groups

• Department of Space, Earth and Environment, Division of Geoscience and Remote Sensing, Chalmers University of Technology, Gothenburg, Sweden
• Department of Atmospheric and Environmental Sciences, University at Albany, State University of New York, Albany, USA
• State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China
• State Key Laboratory of Earth Surface Processes and Resource Ecology, Faculty of Geographical Science, Beijing Normal University, Beijing, China
• Regional Climate Group, Department of Earth Sciences, University of Gothenburg, Gothenburg, Sweden
• Stockholm Resilience Centre, Stockholm University, Stockholm, Sweden

Short Summary

This study reveals that sub-diurnal asymmetric warming, characterized by a faster increase in daily maximum temperature (Tmax) relative to daily minimum temperature (Tmin), has significantly amplified atmospheric dryness (vapor pressure deficit, VPD) over land since the 1980s. This asymmetry has driven a larger increase in saturated vapor pressure (SVP) than actual vapor pressure (AVP), contributing an additional ~18% to the global land VPD increase.

Objective

• To determine whether the faster increases in daily maximum temperature (Tmax) relative to daily minimum temperature (Tmin) have contributed to the rising atmospheric vapor pressure deficit (VPD) since the 1980s, and to quantify the relative importance of Tmax and Tmin in driving VPD variations.

Study Configuration

• Spatial Scale: Global land areas, analyzed at 0.5° × 0.5° grid resolution and using 1398 in-situ observation stations and 56 FLUXNET tower sites.
• Temporal Scale: Main analysis period: 1980–2023 (44 years). Extended analysis for ERA5-Land: 1950–2023 (74 years). Data collected at sub-daily (hourly, half-hourly), daily, monthly, and annual scales.

Methodology and Data

• Models used: Ridge regression, Random Forest (RF) regression, Shapley Additive Explanations (SHAP) framework, Fourier transform-based filtering for seasonal variations.
• Data sources:
  • HadISD dataset: In-situ sub-daily observations (temperature, dew point temperature) from 1398 stations.
  • ERA5-Land reanalysis: Hourly gridded temperature, dew point temperature, soil moisture content (0–28 cm), and total evaporation (approximately 9 km resolution, aggregated to 0.5° × 0.5°).
  • FLUXNET2015 dataset: Half-hourly observations of temperature, VPD, and soil water content from 56 flux tower sites.
  • Self-calibrated Palmer Drought Severity Index (scPDSI): Monthly data from the Climatic Research Unit (CRU) at 0.5° × 0.5° resolution.
  • Fire Weather Index (FWI): Monthly data from the Copernicus Emergency Management Service (CEMS) at approximately 0.25° × 0.25° resolution.

Main Results

• From 1980 to 2023, the faster rise in Tmax compared with Tmin over land intensified VPD. The mean diurnal temperature range (DTR) across all stations increased at an average rate of 0.10 °C per decade.
• Sub-diurnal asymmetric warming contributed an additional ~18% to the increase in global land VPD based on ERA5-Land reanalysis data, and ~30% across sub-daily station observations.
• Interannual variations in saturated vapor pressure (SVP) were primarily determined by Tmax, with Tmax exerting a greater impact on SVP than Tmin across nearly 90% of land areas. A 1 °C increase at global average land Tmax (18.2 °C) results in a 1.35 hPa rise in SVP, which is roughly 72% higher than the rise from the same increase at global average land Tmin (8.6 °C).
• Tmin was the dominant driver of actual vapor pressure (AVP) over 44% of land areas, primarily in mid-latitudes, exerting a positive influence.
• Tmax was generally negatively correlated with relative humidity (RH), while Tmin showed a positive correlation with RH.
• VPD was significantly and negatively correlated with the self-calibrated Palmer Drought Severity Index (scPDSI) across 47.7% of the global land area, indicating a strong link between atmospheric dryness and drought.
• The Fire Weather Index (FWI) showed a significant positive correlation with VPD (93.8% of land area) and DTR (85.7% of land area), suggesting a strong connection between faster daytime warming and heightened fire danger.
• VPD declined from the 1950s to the mid-1970s at a rate of –0.25 hPa per decade, primarily associated with a significant decrease in Tmax (–0.13 °C per decade). In contrast, from 1977 to 2023, VPD increased significantly at 0.31 hPa per decade, paralleling faster Tmax warming (0.30 °C per decade) compared to Tmin (0.27 °C per decade).

Contributions

• Quantifies for the first time the substantial amplification effect of sub-diurnal asymmetric warming on atmospheric dryness, demonstrating its significant contribution to the observed increase in global land VPD since the 1980s.
• Provides a detailed mechanistic understanding of how Tmax and Tmin differentially influence SVP, AVP, and relative humidity, explaining the asymmetric impact on VPD.
• Highlights a critical gap in current Earth system models (ESMs), suggesting that future VPD projections may be underestimated if they do not adequately account for continued global brightening, increasing DTR, and the identified amplification effect of sub-diurnal asymmetric warming.
• Emphasizes the urgent need for improved simulation of future DTR trends and their influence on VPD to enhance predictions of terrestrial water availability, carbon cycling, and the frequency and intensity of extreme events like droughts and wildfires.

Funding

• Chalmers University of Technology (internal funding)
• VAPOR project (grant number 101154385), funded by Horizon Europe, MSCA Postdoctoral Fellowships 2023
• National Science Foundation (grant number AGS-2015780)

Citation

@article{Zhong2025Subdiurnal,
  author = {Zhong, Ziqian and Chen, Hans W. and Dai, Aiguo and Zhou, Tianjun and He, Bin and Su, Bo},
  title = {Sub-diurnal asymmetric warming has amplified atmospheric dryness since the 1980s},
  journal = {Nature Communications},
  year = {2025},
  doi = {10.1038/s41467-025-63672-z},
  url = {https://doi.org/10.1038/s41467-025-63672-z}
}