Drift et al. (2025) Dependence of Convective Precipitation Extremes on Near-Surface Relative Humidity

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Identification

• Journal: Journal of Climate
• Year: 2025
• Date: 2025-08-04
• Authors: Robert J. van der Drift, Paul A. O’Gorman
• DOI: 10.1175/jcli-d-24-0738.1

Research Groups

Not specified in the provided text.

Short Summary

This study uses convection-resolving simulations to demonstrate that reducing near-surface relative humidity (RH) weakens convective precipitation extremes through thermodynamic, dynamic, and precipitation efficiency mechanisms.

Objective

• To investigate the dependence of convective precipitation extremes on near-surface relative humidity (RH), specifically contrasting the conditions over land (where RH is lower and projected to decrease) with idealized ocean-based radiative-convective equilibrium (RCE) simulations.

Study Configuration

• Spatial Scale: Convection-resolving scale (idealized RCE).
• Temporal Scale: Equilibrium states.

Methodology and Data

• Models used: Convection-resolving simulations of Radiative-Convective Equilibrium (RCE).
• Data sources: Model-generated simulation data.
• Approach: A "top-down" experimental design where near-surface RH is reduced by increasing surface evaporative resistance, while free-tropospheric temperatures are held constant by increasing surface temperatures.

Main Results

• Reduced near-surface RH leads to a deeper and drier boundary layer, which weakens convective precipitation extremes via three distinct mechanisms:
  1. Thermodynamic weakening: An increase in the lifting condensation level (LCL) reduces the intensity of precipitation extremes.
  2. Dynamic weakening: The higher LCL reduces positive buoyancy in the lower troposphere, weakening updrafts.
  3. Precipitation efficiency: Increased re-evaporation of rainfall as it falls through the deeper, drier boundary layer substantially decreases the amount of water reaching the surface.
• These effects are physically distinct from the Clausius–Clapeyron scaling (6%–7% K⁻¹) typically observed in constant-RH simulations.

Contributions

• The research highlights that changes in relative humidity can seasonally offset the intensification of rainfall extremes driven by increases in absolute water vapor (specific humidity) over land.
• It establishes the necessity of treating relative humidity as a separate variable from specific humidity when predicting future changes in convective precipitation extremes.

Funding

Not specified in the provided text.

Citation

@article{Drift2025Dependence,
  author = {Drift, Robert J. van der and O’Gorman, Paul A.},
  title = {Dependence of Convective Precipitation Extremes on Near-Surface Relative Humidity},
  journal = {Journal of Climate},
  year = {2025},
  doi = {10.1175/jcli-d-24-0738.1},
  url = {https://doi.org/10.1175/jcli-d-24-0738.1}
}