A study from the University of Utah found that buildings and materials that are created with waterproof materials have an effect on how land absorbs or releases heat energy. This phenomenon causes urban heat islands, developed areas that are hotter than nearby rural areas. For this study, the team focused on the semi-arid Salt Lake Valley, the largest metro area in northeast Utah.

Thermal image showing the surface temperature variation at a Sugar House park site. Source: Carolina Gomez-NavarroThermal image showing the surface temperature variation at a Sugar House park site. Source: Carolina Gomez-Navarro

The team used 60 sensors to analyze the microclimate in five parks in the Salt Lake Valley; Hunter, Lone Park, Midvale City, Southridge and Sugar House. A dozen sensors were placed around the parks and adjacent residential areas that measured temperature and humidity. Photos of the ground around each sensor were captured with satellite images. These images were used to estimate the percentage of roofs, pavement, trees or turfgrass in the area. Images of the canopy cover were gathered by taking photos of the sky above each sensor with a fisheye lens. This software calculated the area of trees that obstructed the sky. They analyzed how the surrounding landscape is impacted the air temperature from June through August 2016.

The results showed that neighborhoods that were made of mostly impermeable surfaces were warmer and driver than the parks. Lawns reduced the daytime and nighttime temperature more than trees. While trees provide shade, lawns act as a swamp cooler. Water moves through the grass, evaporating from tiny holes in the leaves and cooling the air. The more open an area of land is, the better heat can escape into the atmosphere. Areas with trees act like a greenhouse, trapping heat close to the ground. They also found that open landscapes had hotter daytime temperatures and areas with more canopy cover saw more shade reduced temperatures. Turfgrass had nearly the same impact on air temperatures and perceived temperature.

The team concluded that a mixture of trees and grass is the most effective way to cool temperatures in the Salt Lake Valley. The more turfgrass an area had, the lower the temperature was. The next step is to study how different landscapes directly affect how comfortable humans are in their environment and how plant covert types affect soil loss.

This study was published in Agricultural and Forest Meteorology.