Author(s): Rachel Berkowitz

How connected cars can map urban heat islands

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Crowdsourced vehicle data trace the contours of dangerous city temperatures

Early one May morning in 1927 researcher Wilhelm Schmidt attached a mercury thermometer to his car door and drove around Vienna for three hours, recording temperatures. His resulting thermal maps showed hotter areas that coincided with “tightly built parts of the inner city” and cooler contours tracing wooded patches, grassy parks and waterways. Schmidt's efforts were the first to map a city's “islands” of heat in a “sea” of lower-temperature surroundings.

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University of Toulouse meteorology researcher Eva Marques and her colleagues are now updating Schmidt's car technique with modern methodology to chart dangerous heat zones. Their approach uses thermometers in Internet-connected personal cars to map how temperatures can vary over just a few city blocks; such data could help urban planners develop heat-mitigation policies in places without access to sophisticated instrumentation.

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Many cities lack weather station networks that can monitor heat islands comprehensively, so Marques and her colleagues took advantage of Internet-connected sensors that are increasingly becoming standard equipment in cars. First the researchers collected measurements from car temperature sensors in the French city of Toulouse, which has high-resolution weather stations for comparison, and examined how factors such as airflow affected the accuracy of the car-mounted thermometers. Next the scientists created temperature maps in several western European cities using a database comprising millions of car sensor measurements that manufacturers had collected for insurance purposes from 2016 to 2018.

The researchers found they could reliably estimate temperature variations for spaces as small as 200 by 200 meters with fine-grained data collected at 10-second intervals. This method let them assess heat at the street level, where temperatures vary locally based on human activity, 3-D urban geometry and airflows. Their work was detailed in the Bulletin of the American Meteorological Society.

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“Our maps could help researchers improve their understanding of how greenbelts, new buildings and bodies of water impact local thermal variations,” Marques says. Her goal is to make urban climate data available for policy-making processes. For example, her team collaborates with Toulouse municipal officials on making schoolyards greener and prioritizing neighborhoods for upgrades to cool buildings more efficiently—although they are not yet using her car-collected maps. And some small French cities that lack sophisticated weather station networks nonetheless want to use heat maps to assess urban conditions, Marques says. “Crowdsourcing data is a new hope to produce and share maps with these municipalities in the years to come,” she adds.

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