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Urban Heat Island Effect: Causes and Solutions

The Urban Heat Island Effect and How to Fix it

It isn’t your imagination, cities are on average hotter than rural areas. The reason for this is the Urban Heat Island effect.

Traditionally designed cities create and retain heat energy at alarming rates. While you may not consider a slightly increased temperature a huge negative, there are in fact a number of environmental issues that make our overheating cities a big concern that needs to be addressed [1].

Luckily, the solutions available to urban planners are cost effective, low impact and can in fact improve urban lifestyles. Before we look at some available solutions though, we should first better understand exactly how this problem is caused.

The Reason Why Cities are Hotter

There is no arguing with the science, cities are measurably warmer than the surrounding rural areas, but why? The answer comes down to some basic rules of physics, namely the conservation of energy.

Cities are full of life and a lot goes on in a relatively small space. Cars, busses and trains whizz by, joggers, pedestrians and cyclists compete for room on the footpaths. City streets are full of life, and this movement and usage of energy creates waste heat [2].

Waste heat is unavoidable and a natural consequence of movement, but what causes the real problem in large cities is the way in which waste heat is then trapped. Building and paving materials in particular, such as asphalt or concrete are great insulators and retain heat [3].

It is the density of buildings, pavements and parking lots that make our cities hot places to live. It is not a small problem either. EPA figures suggest that in the right conditions, the difference in urban and rural temperatures in the same region can be as much as 12°F [4].

The Hidden Costs of Urban Heat Islands

The problem of urban heat islands is not just one of uncomfortably high temperatures. Unnaturally high ambient temperatures can have a number of financial and environmental costs which are detailed further below.


It goes without saying really that higher temperatures lead to an increased use of cooling, especially in warm climates. The summer months are when this problem is felt most acutely, as the demand for electricity spikes during high demand periods, putting strain on the network and its power generation capabilities [5].

As discovered during research conducted by the EPA, for every 1°F increase after 68°F, energy consumption increases from 1-2% [6]. In the most extreme cases, the increased peak demand can cause brownouts or blackouts.


Waterways that have urban areas within their catchment also suffer the negative consequences of Urban Heat Islands. The previously mentioned hard surfaces that capture and retain heat energy from the town or city maintain higher temperature for a surprisingly long time due to their insulating properties [7].

This heat us is very easily transferred into any stormwater or surface run-off that flows over these surfaces. This unnaturally heated water then enters local waterways, disrupting the ecosystem in a negative way. Many species of aquatic life are highly sensitive to temperature changes and warm water is susceptible to algae blooms which can harm both wildlife and humans if left unchecked [8].


Urban Heat Islands allow species who would not normally inhabit a region due to unsuitable temperatures to thrive, often pushing out native species and disrupting the local ecosystem [9].

Vermin species in particular thrive in warmer temperatures, causing hygiene and public health problems that can be difficult and expensive to address [10].

Solving the Problem of Urban Heat Islands

Urban Heat Islands are clearly a problem that urban planners should look to fix and surprisingly, with just some minor changes can limit the heat trapped by hard surfaces considerably.

Not only do these solutions lower average urban temperatures, many of them create a more liveable and attractive city.

Green Roofs

Although simply changing the color of roofs to a more reflective one, such as white with paint or other surface coverings, there has been a big push toward using ‘Green Roofs’ to combat the Urban Heat Island Effect [0].

Instead of just changing the roof colour, gardens are planted on large city building with flat rooftops. The vegetation is not only attractive, it slows the heat absorption of the roof, lowering the overall amount of retained heat in the building [11].

The best thing is that the garden is relatively cheap to create and maintain and can pay for itself with lower building cooling costs in summer.

More Trees and Gardens

Along the same vein, planting more trees and gardens across the city is a simple and cheap way to lower heat absorption. Trees, shrubs and other ground cover stops the absorption of heat energy and do not retain heat in the same way as hard surfaces [12].

Using gardens for heat mitigation is most effective when they can be used as a replacement for hard surfaces. This method in particular is very low cost and low impact and the vast majority of city residents welcome more trees and gardens as a quality of life improvement.

Fewer Hard Surfaces

One of the most logical solutions to the heat retention problem in urban areas is to limit the use of hard surfaces that use materials that retain heat. This can be put into action by removing existing hard surfaces, or planning new projects with a lower percentage of covered space.

The big problem with this strategy is that hard surfaces are a necessary part of a well functioning urban environment, it is hard to convince planners to reduce their use, as they fear it can reduce the amenity of residents.

Luckily, a new generation of all natural stabilized aggregates are available that can be used as an alternative. Aggregates stabilized by Organic-LockTM are all natural and do not trap heat like concrete or asphalt, yet still provide a hard surface that is durable and
American Disability Association compliant.

Replacing urban paths and trails with stabilized aggregate is cost effective, has a low life cycle cost compared to traditional materials and goes a long way towards lowering urban temperatures.

Green Building Programs

New green building standards, such as LEED have recognized the problem of Urban Heat Islands and address it with their green building standards [13].

In order for a building or project to receive LEED certification, it must meet a range of criteria, including limiting hard surfaces, incorporating greenery and vegetation and using alternative materials that do not cause excessive and unnatural heating or cooling [14].

Even older projects can retroactively become certified if modified appropriately, but the best way to get certified is to have environmental standards in mind during initial planning and construction. Although there can be costs involved, long term benefits include higher resale values and the potential for government tax breaks.

Do Your Part In Eliminating Urban Heat Islands

The next time you are planning an urban project, take into consideration the impact you may be having on the retention of heat.

With some simple design and material choices like using Organic-LockTM in place of other hard surfaces, you can greatly reduce the environmental impact of your development.

Not only does this improve your reputation and standing, it can be a cost effective decision based on low installation costs and affordable long term maintenance.


[1] [11] Norton, Briony & Bosomworth, Karyn & Coutts, Andy & Williams, Nicholas & Livesley, Steve & Trundle, Alexei & Harris, Richard & Mcevoy, Darryn. (2013). Planning for a Cooler Future: Green Infrastructure to Reduce Urban Heat. https://www.researchgate.net/publication/260146703_Planning_for_a_Cooler_Future_Green_Infrastructure_to_Reduce_Urban_Heat

[2] [5] Society, N. (2019). urban heat island. Retrieved 6 November 2019, from https://www.nationalgeographic.org/encyclopedia/urban-heat-island/

[3] [7] Federal Highway Administration (2019). Pavement Thermal Performance And Contribution To Urban And Global Climate. Retrieved 6 November 2019 from: https://www.fhwa.dot.gov/pavement/sustainability/articles/pavement_thermal.cfm

[4] [6] Heat Island Impacts | US EPA. (2019). Retrieved 6 November 2019, from https://www.epa.gov/heat-islands/heat-island-impacts

[8] Kinouchi, T., Yagi, H., Miyamoto, M. (2007). Increase in stream temperature related to anthropogenic heat input from urban wastewater. Journal of Hydrology, Volume 335, Issues 1–2, Pages 78-88. https://www.sciencedirect.com/science/article/pii/S0022169406005877

[9] [10] Seifert, J. (2019). Spring comes sooner to urban heat islands, with potential consequences for wildlife. Retrieved 6 November 2019, from https://news.wisc.edu/spring-comes-sooner-to-urban-heat-islands-with-potential-consequences-for-wildlife/

[12] Guo-yu QIU, Hong-yong LI, Qing-tao ZHANG, Wan CHEN, Xiao-jian LIANG, Xiang-ze LI (2013).
Effects of Evapotranspiration on Mitigation of Urban Temperature by Vegetation and Urban Agriculture,
Journal of Integrative Agriculture, Volume 12, Issue 8, Pages 1307-1315. https://www.sciencedirect.com/science/article/abs/pii/S2095311913605432

[13] [14] Marceau, M., & Van Geem, M. G. (2007). Solar reflectance of concretes for LEED sustainable sites credit: heat island effect. Portland Cement Association. http://kerckhoffstone.com/media/2015/02/Solar-Reflectance-Heat-Island-reduction.pdf


Guardians of the First Amendment Memorial

Installations of Organic-Lock Blended Aggregate at the Guardians of the First Amendment Memorial

Located in Annapolis, Maryland, the Guardians of the First Amendment Memorial honors the lives lost in one of the largest mass killings of journalists in American history. On June 28, 2018, five Capital Gazette journalists were slain in their newsroom, and this memorial opened on the third anniversary as a place to commemorate their lives and the First Amendment that lost their lives defending.

Margies Garden at Whitnall Park


Margie’s Garden, built in memory of local teacher Margaret Kezman, is the children’s addition to the Boerner Botanical Gardens at Whitnall Park in Hales Corners, Wisconsin. The garden is uniquely designed for children and their families, offering an environment that encourages exploration, imagination, and interaction with nature.