Peleg et al. (2025) Hotter summers, heavier showers: Global warming and its impact on Swiss short-duration rainfall extremes

Identification

• Journal: Weather and Climate Extremes
• Year: 2025
• Date: 2025-11-16
• Authors: Nadav Peleg, Marika Koukoula, Jan Rajczak, Sven Kotlarski, Eleonora Dallan, Francesco Marra
• DOI: 10.1016/j.wace.2025.100829

Research Groups

• Institute of Earth Surface Dynamics, University of Lausanne, Switzerland
• Expertise Center for Climate Extremes, University of Lausanne, Switzerland
• Federal Office of Meteorology and Climatology MeteoSwiss, Switzerland
• Department of Land, Environment, Agriculture and Forestry, University of Padova, Italy
• Research Center on Climate Change Impacts, University of Padova, Italy
• Department of Geosciences, University of Padova, Italy

Short Summary

This study quantifies future changes in Swiss sub-daily extreme rainfall using the physically-based TENAX model and Klima CH2025 climate projections. It finds that a 3 °C global warming could increase 10-minute rainfall return levels by up to 40% and hourly extremes by approximately 20%, with greater intensification in high-altitude regions despite an overall reduction in summer rainfall event frequency.

Objective

• To quantify potential future changes in Swiss sub-daily extreme rainfall (10-minute and hourly durations) under different global warming levels, particularly focusing on the magnitude and spatial variability of intensification in mountainous regions like the Swiss Alps.

Study Configuration

• Spatial Scale: Switzerland, specifically 61 MeteoSwiss climate stations covering diverse terrains from lowlands to high alpine regions, analyzed across five major regions (Jura, Plateau, Pre-Alps, Alps, South side of the Alps).
• Temporal Scale:
  • Observed Data: 1981–2020 (all-year for initial comparison), 1991–2020 (warm season: April to October) for reference.
  • Projections: Future periods corresponding to 1.5 °C, 2 °C, and 3 °C global warming levels (GWL) relative to present-day conditions, with regional warm-season wet-day temperature increases of 1.1 °C, 1.8 °C, and 3.3 °C respectively.
  • Event Duration: Sub-daily, specifically 10-minute and 1-hour rainfall extremes.

Methodology and Data

• Models used:
  • TENAX model: "Temperature-dependent non-asymptotic statistical model for extreme return levels" (physically-based statistical model). It decouples extreme rainfall dependence on temperature from rainfall event occurrence, using a magnitude component (Weibull distribution for rainfall intensities with temperature covariate), a temperature component (generalized Gaussian distribution for wet-day temperatures), and a non-asymptotic return level estimation component (Simplified Metastatistical Extreme Value formulation - SMEV).
  • Climate Projections: Klima CH2025 official Swiss climate change scenarios, based on CMIP5-driven EURO-CORDX model ensemble (up to 26 regional climate models).
• Data sources:
  • Observational Data: Station-based data series from Switzerland’s automatic measurement network (SwissMetNet), operated by MeteoSwiss. Includes 10-minute and hourly rainfall and near-surface (2-meter) air temperature data from 61 climate stations for 1981–2020.
  • Climate Model Data: Daily precipitation and temperature time series for each climate station from Klima CH2025 (CMIP5-driven EURO-CORDX ensemble), bias-corrected using quantile-mapping for 1991–2099.

Main Results

• Rainfall-Temperature Scaling: TENAX-estimated rainfall-temperature scaling rates in Switzerland are approximately 10% per degree Celsius for 10-minute extremes and 7% per degree Celsius for hourly durations. Scaling along the Alpine ridge is slightly higher.
• Future Intensification:
  • By a 3 °C global warming level (corresponding to a regional warm-season wet-day temperature increase of 3.3 °C), 10-minute rainfall return levels could increase by up to 40%, while hourly extremes intensify by approximately 20%.
  • Average intensification rates for 1.5 °C (1.1 °C regional warming) are 11.5% (10-min) and 5.4% (1-h); for 2 °C (1.8 °C regional warming) are 20.3% (10-min) and 9% (1-h).
• Spatial Variability: Projected changes show strong spatial variability, with high-altitude regions (Alpine ridge) experiencing greater intensification than lowlands due to stronger rainfall-temperature scaling and an amplified warming rate.
• Event Frequency Shift: Despite an overall reduction in summer rainfall event frequency (4% for 1.5 °C, 7% for 2 °C, 11% for 3 °C GWL), extreme events are expected to occur more frequently. Current 100-year return levels are projected to shift to 30-year return periods in some regions (e.g., 16 years in the Alps, 29 years in the Plateau for 10-min duration under 3 °C GWL).
• Model Validation: TENAX estimates differ by less than 10% from MeteoSwiss observation-based extreme value analyses (GEV method) at 60% of stations for 10-minute and 72% for hourly durations over the 10-year return period.

Contributions

• Provides a detailed, spatially high-resolution assessment of future sub-daily (10-minute and hourly) extreme rainfall intensification in Switzerland, specifically addressing uncertainties and spatial distribution, which was previously lacking with recent Klima CH2025 projections.
• Utilizes the physically-based TENAX model, offering a computationally efficient and robust framework to assess sub-daily changes directly from daily climate model outputs, bypassing the need for additional temporal downscaling.
• Confirms that thermodynamic factors (temperature-driven increases in rainfall intensity) largely outweigh dynamic factors (reduced event occurrence) in shaping future extreme rainfall in Switzerland, aligning with convection-permitting model (CPM) studies.
• Highlights the growing flood risk in Swiss cities (pluvial flooding) and the increasing threat of rainfall-driven hazards (landslides, debris flows) in mountainous areas, emphasizing the urgent need for proactive adaptation measures.

Funding

• Swiss National Science Foundation (SNSF), Grant 194649 ("Rainfall and floods in future cities")
• Department of Geosciences of the University of Padova, Italy ("TENAX" project) as part of "The Geosciences for Sustainable Development" [CUPC93C23002690001]

Citation

@article{Peleg2025Hotter,
  author = {Peleg, Nadav and Koukoula, Marika and Rajczak, Jan and Kotlarski, Sven and Dallan, Eleonora and Marra, Francesco},
  title = {Hotter summers, heavier showers: Global warming and its impact on Swiss short-duration rainfall extremes},
  journal = {Weather and Climate Extremes},
  year = {2025},
  doi = {10.1016/j.wace.2025.100829},
  url = {https://doi.org/10.1016/j.wace.2025.100829}
}