Urban heat islands: dangers and mitigation strategies
February 24, 2025
Urban Heat Islands (UHIs) are a growing concern for cities worldwide, so let’s investigate their causes, impacts and mitigation strategies.
As urban areas expand, the concentration of buildings, roads, and other infrastructure leads to higher temperatures compared to surrounding rural areas (generally between 1 °C to 4 °C higher, though numerous factors can see this number fluctuate, particularly in times of peak heat). This phenomenon, known as the Urban Heat Island effect, poses significant challenges to public health, energy consumption and overall urban livability.
Pavement, buildings and other surfaces that absorb and retain heat can contribute to increased temperatures in urban areas across the entire day.
Understanding Urban Heat Islands
Urban heat islands occur when natural land cover is replaced with dense concentrations of pavement, buildings, and other surfaces that absorb and retain heat. These surfaces can absorb up to 90% of solar radiation during the day and slowly release it at night, leading to higher temperatures in urban areas across the entire day. There are also other factors that contribute to UHIs, including reduced vegetation, increased energy consumption, and the heat generated by vehicles and industrial activities.
As seen here in Planwisely, the urban heat island effect can increase average temperatures dramatically.
Impacts of Urban Heat Islands
The effects of urban heat are far-reaching and multifaceted; however, the most pressing concern might just be public health. In Australia, major heatwaves have caused more deaths since 1890 than bushfires, cyclones, earthquakes, floods and severe storms combined. The effects of extreme heat are felt even more keenly in urban heat islands, which only serves to exacerbate issues like heat-related illnesses, particularly among vulnerable populations such as the elderly and children.
Another undeniable effect of UHIs is an increase in energy consumption. Higher temperatures lead to increased demand for air conditioning, resulting in higher energy consumption and costs. This, in turn, can strain the power grid and increase greenhouse gas emissions. A 2017 study involving Sydney Water, UNSW and Low Carbon Living CRC found that energy consumption for cooling purposes in the UHI-affected Western Sydney region were up to 100 per cent higher than in the eastern zones of the city, and that peak electricity demand almost doubled when temperatures increased from 20 °C to 40 °C.
The effects of urban heat have been observed and studied in different areas of Sydney, Australia.
In addition to these acute effects, urban heat islands also degrade local ecosystems that are sensitive to changes in temperature. These negative effects can initiate and accelerate the demise of green spaces close to UHIs, which in turn increases their size and impact.
Urban heat mitigation strategies
Despite their prevalence and the dangers they pose, there are effective and proven strategies to mitigate the impacts of urban heat.
Beyond the broader conversation of climate change, the most effective (and most obvious) strategy to combat urban heat is increasing green cover in urban areas. Plants and trees help reduce the heat island effect by shading heat-absorbing surfaces in the built environment and by releasing water vapour that in turn lowers surrounding air temperatures. Urban greening or installing green roofs and walls – which can have added stormwater management and insulation benefits – are becoming more of a common practice in urban development, too.
Green roofs and walls have the potential to counter urban heat by covering heat-absorbing surfaces and cooling surrounding air temperatures through evapotranspiration.
Another modern strategy for combatting urban heat is designing urban areas with natural or man-made bodies of water, which is proven to be one of the most effective ways of cooling an urban environment. Wetlands, ponds, fountains or otherwise have an evaporative cooling effect while also providing a ‘thermal oasis’ for people to cool off and find relief from urban heat.
Creating places for people to gather and cool off is a tactical approach to combatting urban heat.
In addition to covering heat-absorbing surfaces and other methods of cooling urban areas, more effort is being given to producing and implementing reflective materials for roofs and pavements, helping to reduce heat absorption in buildings and surfaces and manage urban heat.
Each of these varied strategies play a part in mitigating the impacts of urban heat islands and creating more livable, resilient and sustainable environments. Plus, with climate change and the ongoing development of the urban environment showing no sign of abating, the importance of managing the problem will continue to rise. To help planners tasked with this challenge, Planwisely features a range of datasets and analytics tools for understanding environmental hazards (such as urban heat islands) and creating effective strategies for combatting them.
