Study: Impervious materials are causing cities to be hotter than rural areas
Siobhan Treacy | October 14, 2020A 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-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.
The study, as posted, seemed to leave a big hole in the study's design. An assumption of pervious surfaces = available water for evaporative cooling, vs. impervious surfaces = no evaporative cooling, is apparent. Related variables appear to be uncontrolled or ignored. Urban "heat islands" is a phenomenon that has been well documented for many decades. The study's recommendation that urban areas would benefit from more growing surfaces is good.
--JMM
This is true and not new information. Because most of the sensors in the world are in cities that are getting larger, the climate change data is skewed.
In reply to #2
Friend,
When the data from the sensors are analyzed and correlated with sensor location the climate change data are somewhat different but still remain significantly in the same direction. So, I think I agree with you--just depends on the amount of "skew".
--JMM