Indoor heat in Amsterdam: Comparing observed indoor air temperatures from a professional network and from a citizen science approach

Ongoing climate change is increasing summertime temperatures, and frequency and intensity of heatwaves in Europe, which can threaten human health. Relatively little is known about how quickly outdoor heat penetrates into residences during heatwaves. Long-term and systematic networks recording indoor temperatures are challenging to install and maintain, and therefore scarce. We first report on crowdsourced indoor air temperature data in residences in Amsterdam (The Netherlands) during a heatwave event in September 2023. These data complement professional long-term indoor air temperature observations in 92 houses in Amsterdam. Second, we document the lessons learnt in the design and execution of this citizen science activity. 571 indoor temperature records were collected through the citizen science crowdsourcing approach, with a median value of 28.0 °C on the warmest day in the study period, while outdoor mean minimum and maximum temperatures reached 20.6 °C and 31.1 °C respectively. The results indicate that the crowdsourcing approach reports temperatures that are significantly higher than the professional approach, which supports the need for professional indoor networks. Finally, local media attention was critical in reaching a wide audience.