The combination of heat waves with the aggregation of numerous concrete buildings in urban environments causes an unprecedented temperature rise, a phenomenon that is also known as the "urban heat island" effect. Cities with a population of more than 1 million people may experience a temperature difference of 1°C–3°C during the day and of 12°C during the night compared to nearby rural regions.
"Urban heat island" effect results in increased levels of pollution and may cause severe health issues, especially for young people and the elderly.
Currently, experts from Portland State examine the potential solutions of the problem. Those include planting vegetation and using reflective materials on the buildings' surfaces.
The study, published in journal Atmosphere, investigates on the temperature changes in different types of urban neighborhoods from those filled with vegetation to industrial areas that lack of plant life. Authors used computer modeling and simulated building roofs covered with trees and materials enabled to reflect heat waves placed both in roads and roofs.
The simulations showed that those approaches indeed ameliorated the situation. Roofs with vegetation provided localized cooling in addition to some subsequent benefits (pollution reduction and storm water management). According to Vivek Shandas, Associate Professor in Urban Studies and Planning at the Portland State University and lead author of the study, the findings are significant but the green roofs solution must be further investigated before being promoted as the ideal approach.
Authors also investigated on the consequences of the opposite procedure (removing the existing vegetation and replacing it with pavements). The results showed that this attempt could cause a temperature rise of about 13°C during summer.
The study has also included interactive maps showing the vegetation percentage and pollution indices in every piece of land in Portland.
The findings will be thoroughly examined by city officials and can be used for the future development of Portland.