For the past month, two trucks outfitted with weather sensors, lasers and balloons have roamed Arizona’s scorching cities measuring the heat in extraordinary detail. Such a ground-level view of urban “microclimates” could help cities keep people cool more effectively as climate change boosts temperatures.
“Arizona has been the most extreme environment where we’ve deployed so far because of the intensity of the heat,” says at Brookhaven National Laboratory in New York, who is leading the survey. On the team’s first day in Phoenix, temperatures were so high many of the sensors shut down. “Our lasers are sounding the alarm,” she says.
The trucks are part of a broader effort to understand how heat works in cities at a scale relevant to people. Due to their lack of vegetation and abundance of heat-absorbing concrete and buildings, cities tend to have higher temperatures than surrounding areas. But such urban heat islands also occur between neighbourhoods within cities, or even between blocks. Often, the poorest parts of cities are also the hottest.
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Satellites can take the temperature of the land surface at high resolution. But this doesn’t capture factors in the complex topography of a city that determine people’s experience of the heat, such as air temperature, wind speed and humidity, says at Montana State University, who was not involved in the study. “People assume we have a better understanding of urban climate than we actually do.”
Lamer and her colleagues designed the trucks they call “” to fill this gap. The trucks are bristling with dozens of sensors to scan the urban environment as they rove about. The equipment includes radar to detect clouds, lasers to measure air pollution and weather balloons that take measurements high above street level.
The trucks have been used to measure urban heat in New York City and in Houston, Texas, quantifying the of parks and how can trap or help ventilate air pollution at street level. Now, the researchers are monitoring the much more extreme heat of the US Southwest.
For the past month – the survey concluded on 3 July – the researchers conducted surveys in Phoenix and Tucson, Arizona, both rapidly growing cities that have seen sweltering heatwaves this year. In Phoenix, broke 38°C (100°F) every day in June. “When you’re actually there in the field, you really feel it,” says Lamer.
The number of people who are either homeless or who work outdoors without good options to stay cool was also “eye-opening”, says Lamer. “Any decrease in temperature would be to their benefit.”
While the temperatures were extreme, the heat wasn’t the same everywhere. At one point, the researchers measured a 3 to 4°C (5.4 to 7.2°F) difference between downtown Phoenix and a green space on the outskirts of the city. The region’s ubiquitous golf courses also seemed to have a cooling influence on nearby areas, although no formal analysis has yet been completed. “I could feel a temperature difference, but the numbers will tell,” says Lamer.
Once analysed, observations collected by the trucks will to develop urban climate models that can represent the interactions between weather and the built environment. Ultimately, Lamer says this could help urban planners understand how the placement of a park or the configuration of street trees will affect the heat, block to block. “The same solution might work at one place, and not work in another place,” she says.
