Rooftop rainwater sprinkler systems could help cool warming cities, study says

Researchers led by Zhonghua Zheng at the University of Manchester modeled a system combining rooftop rainwater tanks with sprinklers that trigger at set temperatures, using Tokyo as a case study. The model, published in Earth's Future, found the approach could meaningfully reduce both indoor and outdoor temperatures during heat waves by relying on evaporative cooling.

Urban heat islands can run 15 to 20 degrees Fahrenheit hotter than surrounding land at midafternoon, and a minimum of 35,000 excess deaths were recorded in Europe during heat waves this summer. The researchers say the system uses existing rainwater rather than straining municipal supplies, and could also help with runoff and flooding, though they emphasized cooling benefits most.

Outside scientists cautioned the idea needs real-world testing on actual buildings before anyone gets excited, and that it may work less well in already-humid tropical climates. Cost and feasibility for individual homes versus whole neighborhoods remain open questions.

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