Hotter summers, heavier showers: Global warming and its impact on Swiss short-duration rainfall extremes

Short-duration extreme rainfall events are the main trigger for natural hazards such as flash floods and debris flows. As a result of climate change, extreme convective summer events are expected to intensify markedly in mountainous regions such as the Swiss Alps, although the magnitude of intensification on a sub-daily basis is uncertain. Here, we quantify potential future changes in Swiss sub-daily extreme rainfall using the physically-based TENAX model, which captures the dependence of extreme rainfall on temperature. An independent evaluation against MeteoSwiss observation-based extreme value analyses shows that TENAX estimates differ by less than 10% at 60% of stations for 10 min and 72% for hourly durations over the 10-year return period. TENAX-estimated rainfall-temperature scaling rates in Switzerland are around 10% ° C −1 for 10-min extremes and 7% ° C −1 for hourly durations. Applied with the Klima CH2025 climate projections that are CMIP5-based, results indicate that by the time global warming attains a 3 °C temperature increase compared to present-day conditions, 10-min rainfall return levels could increase by up to 40%, while hourly extremes intensify by approximately 20%. The projected changes exhibit strong spatial variability, with high-altitude regions experiencing greater intensification than lowlands due to stronger rainfall-temperature scaling and an amplified warming rate. Despite an overall reduction in summer rainfall event frequency, extreme events are expected to occur more frequently, with current 100-year return levels projected to shift to 30-year return periods in some regions. These results highlight the growing flood risk in Swiss cities and the increasing threat of rainfall-driven hazards in mountainous areas, underscoring the urgent need for proactive adaptation measures. • Future rainfall return levels in Switzerland are projected using the TENAX model. • 10-min and hourly durations were examined. • Rainfall-temperature scaling and warming rates are lower in valleys than in highlands. • Projections reveal a large increase in rainfall extremes, notably along the mountains. • Extreme summer rain may triple under 3.3 °C Swiss warming compared with 1991–2020.