Many large cities across the world are in danger of becoming all but unlivable due to rising local temperatures. In cities, air, surface and soil temperatures are almost always warmer than in rural areas, with temperatures often up to 10C hotter. This is the urban heat island effect. Urban heat islands are most evident in both warmer surfaces, and aerial temperature observations near the ground.
WHAT CAUSES THE URBAN HEAT ISLAND EFFECT?
A major reason is the reduced number of trees and plants in urban areas. While vegetation tends to cool down surrounding areas by evaporating water, paved urban landscapes often absorb heat. As a result, water runs off instead of seeping into the ground.
The below thermal image of Melbourne’s Royal Parade shows how trees can cool urban areas. While the road is around 60oC, areas under trees are around 30oC cooler on average. Even a 5% fall in urban tree cover can lead to a 1-2oC rise in air temperature.
The placement and design of buildings can also increase temperatures. Tall buildings are often built close to one another, trapping heat by slowing air movement. Also, dense and dark-coloured building materials such as asphalt can store large amounts of heat. These combine with excess heat from industry and transport, to create urban heat islands.
REDUCING THE URBAN HEAT ISLAND EFFECT
If temperatures continue to increase, the health and wellbeing of our communities could be under threat. Air conditioners are often turned to as a solution, feeding a vicious cycle as these tend to emit waste heat outside. Though urbanisation often causes urban heat islands, we can reduce it by changing our cities to absorb less heat. Some ways include building with light-reflecting materials, and planting trees in places with less vegetation.
So how exactly do trees lower temperatures?
They provide shade to cool building interiors while blocking the sun’s heat to cool the surrounding air and soil, and helping water evaporate. This means buildings will not need air conditioning as often, allowing people to save energy and reduce air pollution.
GREENER MEANS CLEANER
Urban forests could make all the difference between healthy cities and unbearable ones. Hence, we should encourage regulations that motivate more greenery in our cities. Several cities across the world have done this, including Seattle, Berlin, Toronto and Singapore.
Otherwise, you can help by growing plants in your backyard or balcony, or joining a tree planting club such as Trees For Life. Every tree helps reduce temperatures and makes your city healthier.