Find a way to control the heat of the city-ScienceDaily

In cities, heat is often intensified and amplified. This is a phenomenon known as the urban heat island effect. Asphalt, concrete, and similar materials absorb and retain much more heat than vegetation, so urban temperatures are often 10 degrees Fahrenheit higher than in the surrounding suburbs and rural areas. In areas with few trees and green spaces, this heat often disproportionately affects older people, low-income communities, and some color communities.

Rooftop greening is designed to harness the cooling power of plants to reduce the temperature of urban spaces. Greens can be vast (shallow soil, less maintained plants) or concentrated (deeper soils, more diverse plants and trees).

The GISS team is investigating three sites in Chicago to see how rooftop greening affects the surface temperature around those buildings, and between those sites and other nearby sites without rooftop greening. I checked if there was a difference. Two of the three rooftop greens in the study lowered temperatures, but the results showed that efficacy could depend on location and plant diversity, among other factors.Results were recently published in the journal Sustainable cities and societies.

Study rooftop greening in the urban jungle

Christian Braneon, a climate scientist and civil engineer at Columbia University and GISS, said: “It is important to understand how these urban design interventions are effective in more frequent heat waves and more extreme heat situations.”

Braneon and the GISS team worked with Chicago’s Public Health and Planning and Development Department to survey three sites that installed green roofs in the early 2000s: Millennium Park, City Hall, and Wal-Mart Shopping Center. Using images captured by the Landsat 5 satellite between 1990 and 2011, researchers compared changes in surface temperature and vegetation at the research site and a nearby control site without rooftop greening.

Results from the three sites were mixed. Millennium Park, which is densely populated with plants near Lake Michigan, has seen a significant drop in average temperature after the rooftop greening was installed in 2004. During the study period, rooftop greening was the only place where climate warming was completely mitigated.

The city hall, which is also a centralized site, installed a rooftop greening in 2002. After the rooftop greening was installed, the temperature was lower than that of the control site, but it increased toward the end of the survey period.

Wal-Mart’s site told another story. Millennium Park and the rooftop greenery of the City Hall were added to the existing building, but a new supermarket was built during the study period. Wal-Mart installed a vast rooftop greenery, but the change from vacant grassland to stores reduced the landscape’s vegetation index.

“In many places, we may be developing areas where something wasn’t there before. It’s just overgrown with vegetation,” said Braneon, co-leader of urban studies at GISS’s Climate Impacts Group. .. “You may think that greening a new building will have a big impact, but it can also add a lot of impermeable material, such as parking lots around the building. As a result, you can park. It may reduce the impact of the parking lot, but it certainly does not produce the cooling effect of the overgrown vegetation. “

Scientists say that the benefits of rooftop greening depend on a variety of factors, from geographic areas and plant diversity to the cooling efficiency of the rooftop structure and the building itself.

Research on larger sample sizes is needed to disperse these details, but this research represents a promising start. Understanding these variables becomes more important as the effects of the urban heat island are expected to increase as the Earth’s climate warms.

The research method is designed to be used in other cities for further research, said Kathryn McConnell, lead author and candidate for a PhD in the Faculty of Environment, Yale University. Simple analysis, published data, and models for direct integration with cities help city planners assess the feasibility of rooftop greening in their area.

“We hope that the method we have proposed shows a low-cost way for people working in resource-poor cities (which may not be accessible to university and government researchers) to study their communities. “We do,” said McConnell. ..

“Traditionally, civil engineers and urban planners assumed a steady climate,” Braneon added. “The whole practice is based on the premise that we can look at the past and assess future risks. Civil engineers and urban planners practice because everything is bothering us because of climate change.”