As our climate changes and temperatures continue to rise, it is increasingly important that we talk about heat, both in terms of heat waves and heat islands. Most people are familiar with heat waves in some capacity and in pop culture we see them depicted playfully with melting popsicles and children playing near open fire hydrants. Rarely, however, do we see the dark side of these heat events.  According to the EPA, “more than 100,000 Americans have died from heat effects since 1979.” While these severe temperature events are unhealthy for all populations, many groups and communities are especially vulnerable. This long list includes elderly people over 65 (with risks increasing over 85 years of age) as well as houseless people and low-income communities who lack access to adequate air conditioning and cooling.  

Urban Heat Islands 

While heat waves may be natural events, urban heat islands are largely the result of our built environment. Many urban spaces feature large expanses of asphalt, concrete, and other black top surfaces. As these dark surfaces heat up, they absorb and trap heat and raise the surface temperature around them. This rise in surface temperature is what then leads to heat islands because, even if the air temperature that we base our forecast on says one thing, the surface temperatures are what we feel in our day to day lives and are influenced by the built environment around us. More specifically, the concept of urban heat islands refers to the heat difference between urban and suburban areas and the rural areas that surround them. This temperature difference can be anything from 1°F to as high as 22°F when comparing the two environments. Many people have experienced the heat island effect on a smaller scale without knowing it. Something as simple as walking on grass barefoot versus walking on asphalt barefoot during the summer makes this effect painfully clear. 

Urban Cool Islands 

In the same way that black top and other dark surfaces raise surface temperatures and cause the heat island effect, green-blue spaces like vegetation and water can lower surface temperatures and create urban cool islands (UCIs). Though they are not studied as much as urban heat islands, urban cool islands may be the key to the projected increase in frequency and intensity of heat waves due to climate change. Green- blue spaces refer to vegetation like trees, shrubs, and grass, and bodies of water like pools, oceans, lakes, rivers, and streams. As plants in green spaces absorb carbon dioxide, they produce oxygen and, through transpiration, cool the air around them as the water inside turns to vapor and evaporates. In addition to the cooling effect of evaporation, trees provide shade for sidewalks and roads which in turn cools down the surfaces that would otherwise contribute to the heat island effect. Blue spaces, like lakes and rivers, cool the air around them, not just through evaporation, but through the breezes caused by the temperature difference between the land and water. 

Urban Heat Islands and Environmental Justice

From an environmental justice point of view, heat islands are an issue that demands urgent action and education. The list on the right shows a larger list of vulnerable communities, many of which already experience several environmental burdens in regards to air quality, clean water access, food security, and poverty. These factors can make it more difficult to deal with, and recover from, heat waves and the heat island effect. 

The reason why a disproportionate number of minority communities live in urban heat islands can be traced all the way back to redlining. From the 1930s to the late 1960s, Black and other people of color were denied housing loans in neighborhoods. This racist housing practice continues to hurt minorities today because the neighborhoods that they were pushed into have been historically underinvested in. NPR cites a study that shows that “In a study of 108 urban areas nationwide, the formerly redlined neighborhoods of nearly every city studied were hotter than the non-redlined neighborhoods, some by nearly 13 degrees.”. This is the legacy of redlining and is yet another reason why we need to act now and work to protect our most vulnerable communities.  

What Can We Do? 

One answer to this growing problem is to invest in green infrastructure and working with these communities to make sure that their needs are met on a daily basis and not just in the aftermath of a disaster. Green infrastructure can take many forms, and includes everything from planting trees alongside streets and within parks, green roofs that double as community gardens, and even the planting of native plants in open spaces. Other forms of infrastructure that can help support vulnerable communities in dealing with heat islands and heat waves are accessible cooling stations, improved public transportation, access to clean water for both recreation and drinking, and improving access to adequate and cost-effective air conditioning.  

As we begin to plan Delaware’s response to climate change, initiatives and programs targeted at mitigating the harm done by heat islands and heat waves must be included in our solutions. It is crucial that we are including the voices of our most vulnerable as we search for these solutions and that we begin to get to the bottom of the social inequities that then lead to community experiences of environmental injustice.  

Marissa McClenton is the author of this blog and a student at University of Delaware as well as the Clean Water Campaign’s Grassroots Organizer. Stay tuned for more insights and resources from the DEIJ Corner and Marissa in the future!