Past, present and future (urban) climates of Bern, Switzerland

In the city of Bern, Switzerland, two urban measurement campaigns were operated by the University of Bern in the periods 1972 to 1974 and 2018 to 2024. In the first campaign, air temperature was measured at six locations with a resolution of two hours, in the second campaign at 55 locations with a resolution of 10 minutes. The summer (June to August) air temperature data of both measurement campaigns was homogenized and corrected for three variables: daily minimum temperature (T_min), daily mean temperature (T_mean), and daily maximum temperature (T_max). The data from the second measurement campaign was subsequently used to simulate urban temperatures in Bern during the currently used reference period (1991 to 2020) and for three global warming scenarios (Global warming level (GWL) 1.5 °C, 2.0 °C and 3.0 °C). To do so, a two-step quantile mapping approach (which includes a transfer function from rural to urban stations) was applied, since the original urban dataset is too short for a direct quantile mapping. Finally, a dataset of three temperature variables for six to 55 locations in and around the city of Bern during six different periods was created.

In this poster, we illustrate the calculation of this dataset and highlight the results regarding calculated heat indices (tropical nights and official heat warning levels). We show that the heat warning thresholds, which were never hit in the first measurement campaign, are reached at almost all locations in the second campaign. We furthermore discuss the differences between the GWL scenarios and the importance of the urban heat island effect during past, present and future (urban) climates of Bern.