Heat waves are among the deadliest and most common of environmental extremes. As the earth continues to warm due to the buildup of greenhouse gases, heat waves are expected to become more severe, particularly for cities, where concrete and a dearth of trees create what's known as the urban heat island effect. Using a global climate model, researchers measured how severely heat waves interact with urban heat islands, now and in the future, in 50 American cities across 3 climate zones. In terms of relative temperature increase, today's Eastern and Southeastern cities are more severely affected by heat waves than arid and semiarid Western cities. This is because of the amount of impenetrable, concrete surfaces and lack of moisture in Eastern and Southeastern cities compared to their rural surroundings. In contrast, both rural and urban dry environments experience similar temperature increases, and both have less annual rainfall than their Eastern and Southeastern counterparts. However, by 2100, this is expected to flip. Arid cities like Phoenix will become hotbeds for heat waves compared to their rural surroundings, while cities on the Eastern seaboard will be less severely affected by heat waves compared to theirs. This is because future arid cities will remain water-limited due to the lack of permeable surfaces in cities, while their rural neighbors are projected to be no longer "dry" due to higher rainfall.
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