Nayak et al. (2025) Regional and vertical scaling of water vapor with temperature over Japan during extreme precipitation in a changing climate

Identification

• Journal: Scientific Reports
• Year: 2025
• Date: 2025-10-15
• Authors: Sridhara Nayak, Tetsuya Takemi
• DOI: 10.1038/s41598-025-22287-6

Research Groups

• Research and Development Center, Japan Meteorological Corporation, Osaka, Japan
• Disaster Prevention Research Institute, Kyoto University, Kyoto, Japan

Short Summary

This study investigates the regional and vertical scaling of atmospheric water vapor with temperature over Japan during extreme precipitation events in present and future climates. It finds a strong positive relationship between specific humidity and temperature in the lower atmosphere, with a rate of change of 8.3 ± 2.4% per degree Celsius, indicating increased intensity of extreme precipitation in a warming climate.

Objective

• To investigate the regional variation of Clausius-Clapeyron (CC)-like scaling of extreme precipitation events across the coast, interior, and seven regions of Japan in the present (1951–2010) and future (2051–2110) climates.
• To examine the scaling of moisture content (specific humidity) at different pressure levels of the troposphere with respect to temperature during wet days across these regions.
• To explore the vertical profile of the rate of change of specific humidity with temperature on wet days to understand the dynamics of moisture and precipitation extremes over Japan.

Study Configuration

• Spatial Scale: Seven distinct regions of Japan (Sea of Japan side of North Japan, Sea of Japan side of East Japan, Sea of Japan side of West Japan, Pacific Ocean side of North Japan, Pacific Ocean side of East Japan, Pacific Ocean side of West Japan, and Okinawa), as well as generalized coastal and interior regions. Model resolution: 20 km (d4PDF), 0.25 degrees (APHRODITE).
• Temporal Scale:
  • Present climate: 1951–2010 (d4PDF), 1961–2015 (APHRODITE), 1980–2022 (MERRA-2).
  • Future climate: 2051–2110 (d4PDF).

Methodology and Data

• Models used:
  • database for Policy Decision making for Future climate change (d4PDF) ensemble simulations (50 ensemble members for present climate, 90 for future climate), utilizing 60-km global and 20-km regional atmospheric models, with warming data from MIROC5.
• Data sources:
  • Asian Precipitation—Highly—Resolved Observational Data Integration Towards Evaluation (APHRODITE) daily datasets (observational).
  • Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) (reanalysis).
• Methodology:
  • Wet days defined as daily precipitation exceeding 1 mm.
  • Daily precipitation, specific humidity, and relative humidity on wet days stratified into 1 °C temperature bins.
  • 99th percentile values computed for each temperature bin.
  • Rate of change of specific humidity with temperature calculated using the equation: P₂ = P₁(1 + α)ΔT, where α is the rate of change.

Main Results

• A strong positive relationship between specific humidity and temperature was found on wet days in the lower atmospheric levels over Japanese regions, while no significant relationship was observed at higher levels.
• The rate of change of specific humidity with temperature on wet days varied by region, falling within the range of 8.3 ± 2.4% per degree Celsius. At the 1000 hPa level, the rate was 6.8–7.3% per degree Celsius, closely following the Clausius-Clapeyron (CC) scaling.
• Extreme precipitation events exhibited a CC-like scaling with temperature up to a certain threshold (e.g., 21 °C in northern regions, 27 °C in Okinawa).
• In a future warming climate, the CC-like relationship for extreme precipitation events is projected to extend to a higher temperature range by 2–4 °C, and for specific humidity by 4 °C.
• Intensities of extreme precipitation events are anticipated to increase in the future, by approximately 10 mm/d over North Pacific, East Pacific, and North Sea of Japan regions, and by approximately 20 mm/d over other regions.
• Coastal regions exhibited the CC-like relationship up to approximately 23 °C, while interior regions showed it up to around 20 °C.
• Relative humidity at 850 hPa showed the highest values among all pressure levels and is projected to remain above 80% over a wider temperature range in the future, contributing to stronger precipitation events.
• An increase in upward motion (vertical velocity) at 700 hPa was observed in the future climate, suggesting enhanced convective activity that amplifies extreme precipitation.

Contributions

• This study is the first to investigate the scaling of water vapor at multiple pressure levels of the free troposphere and its direct relationship to temperature in the context of extreme precipitation events over Japan, for both present and future warming conditions.
• It provides novel insights into the vertical profile of the rate of change of specific humidity with temperature on wet days across different regions of Japan.
• It highlights the regional variability of the CC-like scaling of extreme precipitation and moisture, differentiating between coastal and interior areas, and across seven distinct Japanese regions.
• The research demonstrates that both thermodynamic (increased moisture availability) and dynamic (enhanced vertical motion) factors contribute to the intensification of extreme precipitation under future warming scenarios.

Funding

• Integrated Research Program for Advancing Climate Models (Grant Number JPMXD0717935498)
• Advanced studies of climate change projection (Grant Number JPMXD0722678534)
• Environment Research and Technology Development Fund JPMEERF20192005 of the Environmental Restoration and Conservation Agency
• Data Integration and Analysis System (DIAS, Project No. JPMXD0716808999)
• Japan Society for the Promotion of Science (JSPS) Scientific Research 24H00369

Citation

@article{Nayak2025Regional,
  author = {Nayak, Sridhara and Takemi, Tetsuya},
  title = {Regional and vertical scaling of water vapor with temperature over Japan during extreme precipitation in a changing climate},
  journal = {Scientific Reports},
  year = {2025},
  doi = {10.1038/s41598-025-22287-6},
  url = {https://doi.org/10.1038/s41598-025-22287-6}
}