December 8, 2023

On the first day of May in 1927, researcher Wilhelm Schmidt attached a mercury thermometer to the door of his car while driving around Vienna for over three hours, taking temperature records. The resulting thermal maps revealed warmer areas with “tightly built parts of the inner city” and cooler contours tracing patches of wooded waterways, grassy parks, and grassy areas. Schmidt’s work was the first to identify cities as “islands” of heat within the “sea” of lower-temperature surroundings.

In the 2003 heat wave in Europe, these islands were connected to about 50% of deaths related to heat in some parts of England and to an increase in deaths of the elderly in Paris. The Environmental Protection Agency cites these islands as an essential cause of the 702 deaths related to heat throughout the U.S. on average each year between 2004 and 2018. Over half of the world’s population is living in urban areas, which can exacerbate the local impacts of the rising global temperature–and the suffering is becoming more severe.

University of Toulouse meteorology researcher Eva Marques and her colleagues are now updating Schmidt’s vehicle technique using a more modern approach to track danger zones of heat. They are using thermometers inside automobiles connected to the internet to determine the temperature variations that can occur over only a few blocks of the city. The data can aid urban planners in developing heat-management guidelines in areas without access to advanced instruments.

Urban heat islands happen when the natural vegetation is replaced by asphalt or concrete, steel, or other substances that absorb and store more heat than the surrounding area. They can keep these regions more comfortable, particularly during the night. The heat islands can also impact the quality of air in a city by altering humidity levels and how pollutants are distributed. “With the increase of extreme events like heat waves, city planners need to rethink how urban spaces are designed,” Marques declares.

A lot of cities need weather stations that can detect heat islands in a comprehensive manner and efficiently. Therefore, Marques and her coworkers utilized Internet-connected sensors, which are being used in automobiles as standard equipment. They first gathered data from temperature sensors for cars in Toulouse, a French town with high-resolution weather stations, to compare and study how other factors like airflow influenced the accuracy of car-mounted thermometers. The researchers then developed temperature maps of various Western European cities using a database containing millions of measurements from car sensors that the manufacturers had taken for insurance purposes between 2016 and 2018.


A heat island in the urban area near Toulouse, France, is depicted in a consolidated car thermometer data from summer 2018 nights. More intense colors signify hotter air. Credit: University of Toulouse, Meteo-France/CNRS, France

Researchers found that they could accurately assess temperature variations for areas smaller than 200 x 200 meters using high-quality data taken at intervals of 10 seconds. This technique allowed them to determine heat levels at the surface, where temperature changes local to the extent of human activity and 3-D urban geometry and airflows. The research was published in the Bulletin of the American Meteorological Society.

“Connected vehicle observations related to weather are an underused source of microscale observations,” Amanda Siems Anderson, a researcher at the U.S. National Center for Atmospheric Research (NCAR), who was not a part of the research. “This work demonstrates a novel use for these data.” Iain Stewart, a researcher in urban climate from the University of Toronto, who was not part of the research, says the study “is provocative and points to future possibilities for data retrieval in cities.”

The sensors that are factory-installed in cars can offer a wealth of weather and climate-related data, according to Siems Anderson. The problem is in ensuring the consistency and accuracy of data as well as establishing an infrastructure that can pull these data from sufficient vehicles. For instance, NCAR already collects vehicle data to enhance weather forecasts by utilizing a five-minute daily update system. However, these initiatives “often use 10 to several hundred [dedicated] vehicles, which do not provide adequate coverage unless they’re in a very confined area,” Siems-Anderson explains. Going beyond pilot studies requires a massive increase in the number of vehicles. Quality control is essential in collecting data from cars that happen to be within a particular zone.

Authorities are working to build the capabilities. State and local initiatives across the U.S. aim to install and maintain infrastructure that can collect and analyze connected vehicle data and enhance the accuracy of community-driven climate research. For instance, the U.S. Department of Transportation For example, it has implemented pilot programs in places like New York and Wyoming that keep track of weather and traffic. These data may eventually fill the gaps between fixed weather stations, allowing applications such as mapping and monitoring urban heat islands.

“Our maps could help researchers improve their understanding of how greenbelts, new buildings and bodies of water impact local thermal variations,” Marques states. She aims to make information on urban climate accessible to policymakers. 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. Some smaller French cities without sophisticated weather stations still want to use heat maps to gauge the conditions of their cities, Marques says. “Crowdsourcing data is a new hope to produce and share maps with these municipalities in the years to come,” she says.

According to Stewart, developing high-quality temperature maps for city planning isn’t easy. Crowdsourcing the data required is only in the beginning stages. Maps should ideally incorporate places off-road where people gather. However, eventually, Stewart states, “hot, crowded cities in lower-income regions of the world stand to benefit most” from the crowdsourced thermal maps. Cities with lower incomes in tropical regions have been historically unstudied in urban climate and may need access to the tools that benefit the other areas of the globe. Yet, they are the most susceptible to urban heat.


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