Wan et al. (2026) Integrated relative humidity as a layer-resolved indicator for moisture-precipitation interactions

Identification

• Journal: Scientific Reports
• Year: 2026
• Date: 2026-04-04
• Authors: Moufeng Wan, Hui Su, Chengxing Zhai, Meining Wu, Pak Wai Chan, Shuangchen Du
• DOI: 10.1038/s41598-026-47087-4

Research Groups

• State Key Laboratory of Climate Resilience for Coastal Cities, Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology
• Division of Emerging Interdisciplinary Areas, The Hong Kong University of Science and Technology
• Hong Kong Observatory

Short Summary

This study introduces Integrated Relative Humidity (IRH) as a layer-resolved diagnostic to quantitatively investigate moisture-precipitation interactions in subtropical coastal environments, revealing distinct vertical saturation structures across precipitation lifecycle stages and identifying specific IRH thresholds for precipitation events.

Objective

• To introduce Integrated Relative Humidity (IRH) as a novel, layer-resolved diagnostic for tropospheric saturation.
• To investigate moisture-precipitation interactions in the subtropical coastal environment (Hong Kong) using IRH across different precipitation lifecycle stages.
• To develop a quantitative diagnostic framework using IRH that can inform the development of nowcasting tools and aid in model evaluation.

Study Configuration

• Spatial Scale: Subtropical coastal environment (Hong Kong).
• Temporal Scale: 16 years (2005–2020).

Methodology and Data

• Models used: Integrated Relative Humidity (IRH) diagnostic, computed from the surface to nine standard pressure levels (1000 hPa to 150 hPa).
• Data sources:
  • Co-located radiosonde data from the Integrated Global Radiosonde Archive (IGRA).
  • Rain gauge data from the Hong Kong Observatory.

Main Results

• IRH probability density functions (PDFs) reveal stage-specific vertical structures of saturation, with consistent saturation peaks observed near 850 hPa.
• The Before Rain (BR) stage shows increasing lower-tropospheric saturation, the During Rain (DR) stage exhibits the highest deep-column saturation, and the After Rain (AR) stage displays reduced mid-level saturation, reflecting dynamic moisture redistribution.
• Bimodal PDF structures in BR, DR, and AR stages are consistent with transitions between shallow and deep convective regimes.
• Reversed cumulative distribution function (RCDF) for IRH = 0.90 effectively captures low/mid-level moisture buildup during BR and DR stages.
• RCDF for IRH = 0.80 highlights upper-level moisture dissipation during the AR stage.
• Crucial IRH thresholds for identifying precipitation events were established:
  • An IRH of 0.82 at 700 hPa corresponds to 84% of DR events and excludes 76% of No Rain (NR) cases.
  • An IRH of 0.70 at 150 hPa corresponds to 82% of DR events and excludes 76% of NR cases.
  • The threshold of 0.70 at 150 hPa is also exceeded in 72% of BR events, with the same 76% NR exclusion.

Contributions

• Introduces Integrated Relative Humidity (IRH) as a novel, layer-resolved diagnostic, offering a more detailed vertical understanding of tropospheric saturation compared to traditional column-integrated metrics.
• Provides a quantitative diagnostic framework for analyzing moisture-precipitation interactions across distinct precipitation lifecycle stages in subtropical coastal environments.
• Establishes specific, quantitative IRH thresholds that effectively distinguish between precipitation and non-precipitation events, demonstrating potential for improving nowcasting tools and enhancing climate model evaluation.

Funding

• The Hong Kong Jockey Club Charities Trust (FA123) for the JC STEM Lab of Precipitation and Convection.
• State Key Laboratory of Climate Resilience for Coastal Cities (ITC-SKLCRCC26EG01).
• ITC-RTH scheme (P0413).
• ITF grant (ITP/047/23LP).

Citation

@article{Wan2026Integrated,
  author = {Wan, Moufeng and Su, Hui and Zhai, Chengxing and Wu, Meining and Chan, Pak Wai and Du, Shuangchen},
  title = {Integrated relative humidity as a layer-resolved indicator for moisture-precipitation interactions},
  journal = {Scientific Reports},
  year = {2026},
  doi = {10.1038/s41598-026-47087-4},
  url = {https://doi.org/10.1038/s41598-026-47087-4}
}