As people rely more on air conditioning to stay cool, energy demand increases and waste heat released from buildings can make urban areas even hotter. Urban watering technologies are becoming important ways for reducing extreme heat in cities, but their use is often limited by the availability of water. The cooler roofs transferred less heat into buildings, while lower air conditioning use meant less waste heat was released into the city. Together, these effects helped reduce urban temperatures, cutting the number of heatwave days overall and lessening the intensity of extreme heat events. Junjie Yu, PhD researcher at The University of Manchester, added: “The rainwater tank also provides an additional co-benefit on reducing the extreme urban runoff.