Trees and vegetation are vital components for liveable, healthy suburbs and can assist in reducing what is known as the ‘urban heat island effect’.
Heat islands form in urban and suburban areas because many common construction materials absorb and retain more of the sun’s heat than natural materials in less developed rural areas. Temperatures of dark, dry surfaces in direct sun can reach 88°C during the day, while vegetated surfaces with moist soil under the same conditions might reach only 18°C.
These dark surfaces include roads, roofs and car parks that create artificial warmth or ‘urban heat islands’ in built up areas.
What are the impacts of urban heat islands?
Heat islands play a role in driving higher temperatures in our cities which can result in significant health impacts. In periods of prolonged heat, the urban heat island effect can place additional heat stress on all people, particularly those who are vulnerable to extreme heat such as the elderly, very young and those with existing medical conditions. In the week preceding the 2009 Black Saturday bushfires Melbourne experienced three consecutive days over 43°C. During this time the number of deaths in Melbourne increased from an average of 90 per day to over 200 per day. This resulted in 374 deaths above the normal.
How can trees and vegetation help?
Cooler, shaded spaces in our parks, near buildings, in streetscapes and alongside homes can reduce heat stress, particularly for those in our community who are most vulnerable to high temperatures.
Trees can cool our suburbs and city by providing shade and releasing moisture into the air through evapo-transpiration. Research suggests suburban areas with mature trees are 2-3°C cooler than new suburbs without trees.
Source: Heat Islands: Understanding and Mitigating Heat in Urban Areas, Gartland, L., Earthscan, 2011.