As climate change pushes many cities towards dangerous temperatures, planners are scrambling to mitigate excessive heat. One strategy is to replace artificial surfaces with vegetation cover. In water-limited regions, municipalities have to balance the benefit of cooler temperatures with using precious water for irrigation. A new study will make those decisions easier for the semi-arid Salt Lake Valley, the largest metropolitan area in Utah located in the northern part of the state.

One strategy is to replace artificial surfaces with vegetation cover. In water-limited regions such as Utah, a state with one of the lowest annual rainfall rates in the United States, municipalities have to balance the benefit of cooler temperatures with using precious water for irrigation.

A new University of Utah study will make those decisions easier for the semi-arid Salt Lake Valley, the largest metropolitan area in Utah located in the northern part of the state. The researchers used 60 sensors to analyze the microclimate in five locations throughout the valley. They found that neighborhoods dominated by impervious surfaces were warmer and drier than the urban parks — up to 2 degrees warmer in both the daytime and nighttime.

«It’s intuitive — we’ve all stood in a parking lot on a hot summer day, and you feel the heat from the ground. And when you’re standing on a lawn, it’s cooler,» said lead author Carolina Gomez-Navarro, postdoctoral researcher at the U. «But we need to back up intuition with data to determine the best strategy for our semi-arid cities.»

Gomez-Navarro and the team measured the temperature and humidity inside five parks and in their adjacent residential areas from June through August in 2016. They also analyzed how the surrounding landscape impacted air temperature. Surprisingly, they found that lawns reduced daytime and nighttime temperatures even more than trees did. While trees provide shade, lawns and turfgrass act like a swamp cooler — water moves through the plant, evaporating from tiny holes in the leaves and cooling the air.

Much of the heat that builds up during the day dissipates at night. The more open the land, the better heat can escape into the atmosphere. An area with many trees acts like a greenhouse, trapping heat close to the ground. The study concluded that a mixture of dispersed trees and grass is the most effective way to cool temperatures in the Salt Lake Valley.

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Materials provided by University of Utah. Original written by Lisa Potter. Note: Content may be edited for style and length.