A variety of approaches are being developed to minimize urban heat island effect

Japan Times : Because of buildings, streets, and other human construction, cities absorb more heat than the surrounding countryside. When they absorb so much heat during the day that they don’t cool off over night, a cycle can develop in which temperatures are significantly higher in urban areas than in their outskirts. To combat this urban heat island effect, city planners and architects are developing a mix of high- and low-tech solutions. They include covering roofs with plants or making them reflective, designing buildings that allow for more airflow through the city, planting trees to increase shade, and adding streams to absorb and move heat. But each option comes with challenges. Adding trees to increase shade needs to be done in a way that doesn’t trap pollution or block wind, and adding streams can be difficult in already developed areas. At least 20–30% of roofs would need to be covered with green or reflective materials to be effective.