By 2100, arid cities like Phoenix will become hotbeds for heatwaves compared to their rural surroundings, while cities on the eastern seaboard will be less severely affected by heatwaves compared to theirs. The findings highlight the importance of heat-mitigation strategies and infrastructures such as green roofs.
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 heatwaves compared to their rural surroundings, while cities on the eastern seaboard will be less severely affected by heatwaves 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. The overuse of air conditioners also emits heat into the urban heat islands, playing a significant role.
The findings are tied to urban-rural development. A city’s water availability, through rainfall or irrigation, dictates its evaporative cooling effects on temperature, which reduces the severity of a heat wave. In other words, cities with more moisture will cool more quickly.