The Urban Heat Island Effect: A Looming Threat

The Urban Heat Island Effect: A Looming Threat

By Shakari McGill

More people are living in cities than ever before. To meet the demands of growing populations, cities are also pouring more dark paving and developing more of our natural landscape than ever before. These conditions are a perfect storm for what is known as “urban heat island effect.”

Urban heat island effect occurs when heat from the sun is retained by, rather than reflected by, low albedo surfaces like dark paving. These masses then heat up and slowly release heat into the surrounding air, making the entire area run hotter than is typical. This poses a significant threat to people who reside in these areas because it can cause various health issues. The severity of this threat will only rise as the effects of climate change continue to worsen. Luckily, we have the tools to address the issue and will continue to iterate on them.


Because it further amplifies the heat increase caused by global warming, the urban heat island effect can cause ailments such as heat stroke, hyperthermia syncope, exhaustion, and dehydration. Additionally, it can exacerbate pre-existing conditions like cardiovascular disease. Populations most susceptible include children, elderly individuals, members of disadvantaged communities, athletes, and pets. Death from these complications is entirely possible and, in fact, is a growing concern in Australia, where more individuals are killed by heat than any other natural disaster in Australia.  If left unchecked, increased heat caused by the urban heat island effect could become just as threatening in the U.S.


In terms of addressing this issue through policy, Title 24 in California is a leader. Title 24 dictates that cool roofs – light colored roofs with high albedo and low solar emittance, be used exclusively for non-residential projects. Inclusion of cool roofs is optional for residential structures under this code.

In the context of incentives, the United States Green Building Council (USGBC), identifies methods that can be applied to a variety of structures in its LEED v4 handbook. Specific suggestions for new construction and larger buildings include: installing or utilizing existing plant material to cover paved areas within 10 years of growth, implementing architectural devices/shading structures with solar reflectance values of 0.28 or more, covering parking, and using high-albedo roofs. For new home construction, USGBC suggests using Energy Star-qualified roof products, relying on open pavers, and incorporating shading in the same manner as new construction/larger buildings.    

Moving forward, urban heat island policy and incentives should be prioritized and supported more heavily in disadvantaged communities. Individuals in these communities often live in structures that are poorly insulated and massively inefficient. Many policies and incentives deal mainly with new structures, while there is nothing in place to require or encourage upgrades in older structures. This is especially pressing considering that the majority of homes in California were built in the 1950s. In low-income communities where structures are too old — and therefore too expensive — to improve, these necessary updates often go unconsidered. Legislation demanding heat mitigating retrofits and subsequent funding through government initiatives such as the Sustainable Housing Initiative (SHI), which encourages sustainable building practices through the provision of grants, could help address both issues. But at the rate that our globe is warming and our cities are developing, action needs to be taken soon.

Further Reading:

Reducing Urban Heat Islands: Compendium of Strategies: Heat Island Reduction Activities

Urban Heat Island  

An effective public health program to reduce urban heat islands in Québec, Canada  

Assessing Vulnerability to Urban Heat: A Study of Disproportionate Heat Exposure and Access to Refuge by Socio-Demographic Status in Portland, Oregon

CalEPA Urban heat island Index (data for google maps)