Switzerland is experiencing its fourth heatwave of the season, prompting discussions about whether weeks where the thermometer rises above 30 degrees Celsius have become the norm for many Swiss. According to data from MeteoSwiss, an tool has been developed to track the number of heatwave days (maximum temperature exceeding 30 degrees) in a region since a person’s birth.
The persistence of these high temperatures has raised questions about historical comparisons. While contemporary weather patterns frequently push thermometers past the 30-degree threshold, analyzing these trends requires consideration of how weather stations operate and how data has been recorded. MeteoSwiss has measured temperatures since 1864, but evaluating extreme daily maximums involves specific methodological challenges.
Understanding the historical context of Swiss heatwaves involves looking closely at how temperature data is collected and standardized. MeteoSwiss records temperature measurements across a network of stations, and guidelines govern the placement of these instruments to ensure data integrity. Under standards set by the World Meteorological Organization, weather stations must remain as free as possible from artificial heat sources to maintain long-term observational consistency.
Over the decades, the relocation of several weather stations away from city centers toward peripheral areas has occurred. For example, the Zurich station was moved from the center to the periphery in 1949, while other stations like Basel/Binningen and Bern/Zollikofen are situated on the outskirts of their respective cities. Similarly, monitoring sites in Geneva and Sion are in their respective airports, and the Zurich/Fluntern station sits on the Zürichberg at an elevation of 556 meters.
The Urban Heat Island Effect and Tropical Nights
Because official weather stations are positioned away from city centers, recorded temperatures often differ from what residents experience on their balconies. In town, it is generally hotter than at the measurement station.
Data comparing two sites in Zurich between 1991 and 2020 illustrates this local disparity. During that period, the station in the city center registered an average of eight tropical nights per year. In contrast, the Fluntern station recorded an average of only one tropical night annually during the same period. This contrast highlights that the tool shows the value at the measurement station, not necessarily the value on a balcony.
Data Limitations Prior to 1960
People born in the 1950s and before do not find their birth year in the tool. MeteoSwiss explains that while temperature measurements date back to 1864, long-term homogeneous series since 1864 exist only as monthly and annual values for temperature averages and precipitation.
Calculating specific daily maximums required for identifying heatwave days—defined as maximum temperature exceeding 30 degrees—is different. Because stations have been moved, measuring devices replaced, and the environment built up over the decades, such changes distort comparisons. Consequently, comparable data for heatwave days is not available before 1960.
Next Steps and Official Climate Updates
MeteoSwiss maintains monitoring protocols to track heatwave frequency, duration, and intensity. Residents seeking real-time weather alerts, localized forecasts, and historical climate analyses can consult the official MeteoSwiss portal for regular updates and scientific publications.
Readers are encouraged to share their experiences with recurring summer heatwaves and join the ongoing conversation in the comments section below.