Summary

Urbanization and the growing urban population have exacerbated the Urban Heat Island (UHI) effect. To better understand the extent of exposure and the spatial distribution of health risks associated with the UHI effect, this study assessed the spatial distribution of UHI intensity and vulnerable populations across three Swiss cities: Bern, Basel, and Zurich.

We used publicly available simulated night-time temperature data for the summer of 2020 at a fine spatial resolution. UHI intensity was calculated as the temperature difference between urban areas and rural reference stations for each city. We then identified vulnerable populations with higher mortality risks from extreme heat and the UHI effect, utilizing existing evidence from previous studies. Based on this evidence, we identified older adults (aged > 64 years), females, and individuals with the lowest socio-economic status as vulnerable to the UHI effect in Switzerland.

A key feature of this study is the identification of at-risk neighbourhoods affected by the UHI effect using census and publicly available temperature data. This comprehensive approach can potentially be extended to other cities, offering insights for identifying vulnerable neighbourhoods and the determinants exacerbating heat risks at the district level.

Data

Demographic and socio-economic data

We collected individual-level population and household statistics, referred to as 'STATPOP', from the Swiss Federal Statistical Office for the years 2012 to 2021. For this study, we used STATPOP data from 2020 to ensure temporal consistency with the temperature data. Furthermore, we integrated the Swiss-SEP Index, an area-based indicator reflecting socio-economic position in Switzerland (Panczak et al., 2023).

For workforce information, we used statistics on the Swiss economy, known as 'STATENT', from the Swiss Federal Statistical Office for the year 2020. Using STATENT, we calculated the number of employees by economic sector (agricultural, industrial, and service sectors) by district.

Temperature data

We used simulated night-time (4 a.m.) air temperature data at 2 meters above ground level for the year 2020. This dataset is based on the FITNAH 3D model, which incorporates terrain height, land use structure, and vegetation height (Gross 1989; Gross 1993; Gross 2002). The spatial resolution of the temperature data varied by city: Bern (5m x 5m), Basel (10m x 10m), and Zurich (25m x 25m).

Methods

UHI intensity was calculated as the temperature difference between urban areas and rural reference points. We then computed district-level mean UHI intensity and identified 'High UHI areas' and 'Extreme UHI areas', defined as districts experiencing UHI intensity higher than the city-wide average and above the 90th percentile, respectively.

For detailed information on exposure assessment methods and the development of the heat vulnerability index, please refer to the project report: https://doi.org/10.48620/87094

Information

This website is designed to interactively explore the spatial distribution of vulnerable populations and infrastructure affected by the Urban Heat Island (UHI) effect in Swiss cities. The temperature and demographic data presented on the website are based on the year 2020.

The website provides content solely for informational purposes and may not reflect the most up-to-date developments on the topics addressed.

This project is funded by the NCCS-Impacts Programme, under the project "Impacts of climate change on health, well-being and performance of humans and on food safety in Switzerland." It was developed by Sujung Lee. For any questions or feedback, please contact: sujung.lee@unibe.ch