Heat without relief? Future projections of heat exposure in Swiss cities in a warmer climate

Extremely high temperatures pose a growing threat to human health, especially in urban areas, where limited nighttime cooling restricts recovery from daytime heat stress. By contrast, suburban and rural areas often experience lower nighttime temperatures, which can partly alleviate heat stress. This study examines current heat exposure in urban and rural areas of five Swiss cities – Basel, Bern, Geneva, Lausanne, and Zurich – and how this might change in a warmer future climate. Using the heat warning level concept developed by MeteoSwiss, we evaluate the changes in the frequency and intensity of heatwaves at urban-rural station pairs under global warming of 1.5°C, 2.0°C, and 3.0°C, as projected by the Swiss Climate CH2025 Scenarios. Our results indicate that continued global warming will lead to higher daytime and nighttime temperatures in summer, resulting in substantially greater exposure to heat in both urban and rural areas. Under present-day conditions, heatwaves are relatively rare in these cities. On average, they occur less than once a year in rural areas and once a year in urban areas, lasting approximately three days. Under warmer conditions, they will become more frequent, longer, and more intense, particularly in urban environments, where higher warning levels will be reached more often. At GWL3.0, rural areas are projected to experience an average of three heatwaves per year, whereas urban areas may experience an average of four. Heatwaves will also last longer in urban areas, with an average duration of 14 days compared to 10 days in rural areas. In addition, the season conducive to heatwaves is projected to lengthen. These findings emphasise the growing significance of urban heat exposure as a climate-related health issue in Switzerland. They also underline the importance of robust heat warning systems in supporting timely communication, preparedness, and adaptation planning in urban environments that are becoming increasingly prone to heat.