One of the topics where citizen science can support researchers and environmental agencies more consistently is disclosing the impact of small neighbourhoods to the Urban Heat Island (UHI) effect, the process regulating the temperature difference between a city and its rural surroundings. Being strictly regulated by the city topography, land cover and materials of the built objects, the air temperature within the urban layout can vary consistently from one street to the other, thus providing a differential contribution to the UHI. Air temperature monitoring by citizens can provide simple but reliable additional measurements to depict these street-to-street differences and settle further investigations to reveal the causes (what physical process contributes the most to a certain hotspot) and design solutions (how can we mitigate that hotspot). MeteoTracker are suitable sensors for this investigation allowing a large spatial coverage of measurements with a small commitment from citizens.
In this context, the University of Bologna designed an experimental exercise where volunteering citizens were invited to bike specific tracks in different areas of the city, once per hour for 24 hours, to map the evolution of the UHI within Bologna. An equal number of infrared photos were collected from the top of the second highest tower within the city to depict the temperature of the surfaces, i.e., a forcing of the urban heat. Infrared photos revealed the different thermal footprint of insolated surfaces, different materials (pottery, concrete, …) and vegetation cover, leaving room for useful discussion among the thermal properties of the urban objects and the correct use of them to minimize the hotspot formation. Alongside, the spatial coverage of air temperature owed by the MeteoTracker allowed to compare the city center with the neighborhood of the Sant’Orsola hospital, located outside the historical center, and characterized by lower buildings and vegetation.
These measurements allow for a reflection on the UHI evolution within the same urban environment, also depicting the role of its precursors and evidencing the impact of mitigating factors. They show how small temperature differential during the day between different areas of the same city (insulated surfaces warms at similar rates) can become large during the night (up to 3°C according to late night measurements), owed to the different tendency of materials in releasing the stored heat in time. Despite this activity being largely research-driven, the fundamental co-operation with citizens was essential for its realization. Moreover, it provides useful insight on the UHI effect that can be the basis for inspirational discussions among the participants and relevant public authorities.