New App Cool Routes Shows Pedestrians the Way to Stay Cool in Heatwaves

As a heatwave sweeps across Western Europe, with temperatures soaring in cities like Paris and Warsaw, a new tool from Arizona State University (ASU) offers a potential respite for pedestrians. The Cool Routes application is an online navigation system designed to identify cooler routes by analyzing sun exposure and the temperature humans perceive.

This innovative system goes beyond simply measuring air temperature. It incorporates the impact of direct sunlight and heat reflected from buildings and pavement, providing a more accurate picture of how hot a specific path will feel. In Phoenix, one of the hottest U.S. cities, the difference can be stark: perceived temperatures can exceed 66 degrees Celsius (140 Fahrenheit) in direct sun, plummeting to around 38 degrees Celsius (100 Fahrenheit) in the shade.

Cool Routes updates its data hourly using weather forecasts and factors in the presence of buildings and trees that provide shade. Ariane Middel, director of ASU's SHADE Lab, explained to "Popular Science" that the website functions like a standard navigation map but includes a thermal conditions layer. Instead of just asking "how to get there fastest?", it answers "how to get there coolest?"

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Cool Routes is a website accessible to everyone. The user can open it in a browser, select a starting point and destination on the ASU campus in Tempe, and then see routes that take into account heat exposure.

During tests on the ASU campus in Tempe, the system successfully identified cooler routes over 70% of the time, even reducing perceived heat load by an average of 4.5 degrees Celsius (8 Fahrenheit). Researchers used a mobile monitoring station to verify the results, finding them highly precise. Middel noted that people often don't need to significantly lengthen their journey to reduce heat exposure; a slightly longer path can be considerably more shaded than the shortest one.

While currently limited to the ASU Tempe campus, the technology behind Cool Routes has broader implications. Researchers believe the data collected could assist urban planners in designing cities with more shade, including new tree plantings and overhead coverings, to mitigate the effects of extreme heat.

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One of the most important findings was that people often don't need to significantly lengthen their route to reduce heat exposure. In many cases, a slightly longer route is much better shaded than the shortest one.