How do urban heat islands impact human health?
Urban heat Islands (UHI) pose a serious threat to public health, particularly for children, the elderly, people with respiratory illnesses and those who work outdoors. Higher temperatures can increase the risk of heat-related illnesses such as heat stroke or heat stress and even death. Older adults who are stressed by heat during the day need to cool down and recover at night. But high nighttime temperatures make it more difficult to do so, and increase the risk of heat stroke. High temperatures also intensify air pollution in cities by creating smog, a dangerous pollutant that can make it difficult to breathe, which in turn triggers asthma attacks and spiking emergency room visits. This is particularly concerning because asthma is the most common chronic disease among children.
Get the Latest from American Forests
Stay up-to-date on our urban forestry work, reforestation projects, research and more.
Sign up for emails
People with lower incomes and people of color generally have higher incidences of pre-existing health conditions that make them more vulnerable to heat impacts. And lower-income neighborhoods and communities of color are, on average, much hotter than more affluent White communities. That’s largely due to systemic inequities and discriminatory policies and practices. What’s more, many families in these groups are among the 13 percent of U.S. households that do not have air conditioning. Still others cannot afford to fully operate their air conditioning systems.
How does climate change intensify the urban heat island effect?
Climate change is leading to higher temperatures and longer, more intense and more frequent heat waves. Cities will suffer even more during extreme heat events. Actions like planting and maintaining city trees and other vegetation can help keep cities cool. These actions can also help cities be more resilient to other climate change impacts like reducing flooding and improving air quality.
What role do trees play in mitigating urban heat islands and promoting health?
There are two main techniques that help reduce urban heat islands: using reflective materials on the surface of buildings and roads so they absorb less heat, and using trees and plants to cool the environment. Properly selected and planted trees provide shade to buildings and sidewalks, helping to reduce temperatures. Trees provide additional cooling through transpiration—a natural air cooling effect that occurs when trees release moisture into the air. This is especially beneficial in places where heat is trapped in concrete and asphalt surfaces. And because cool air naturally settles near the ground, temperatures directly under trees can be 20 to 45 degrees cooler than air temperatures in nearby unshaded areas. This is why trees are air conditioning for cities.
Trees also benefit urban areas by making it easier for us to breathe. Trees act as air filters, absorbing pollutant gases and filtering particulates from the air by trapping them on bark and leaves. Trees help filter the air not only to benefit people but also the earth’s ecosystems as a whole. Nationwide, city trees already prevent approximately 1,200 heat-related deaths and countless heat-related illnesses annually. This is particularly critical now, during COVID-19, which disproportionately affects people of color.
Combatting extreme heat amid the COVID-19 pandemic
As temperatures rise across America’s cities and the ongoing coronavirus pandemic strains physical and mental health, more people than ever are seeking refuge in parks. But not everyone is finding that refuge. A study conducted by the Trust for Public Land found that across 14,000 U.S. city neighborhoods, communities of color are more likely to be located near smaller asphalt-filled parks. These parks are also 5 times more crowded than parks serving majority white communities. This disparity in access to the kinds of parks that adequately reduce temperatures and provide cooling calls for a new approach to expanding urban forests and parks.
For these reasons, American Forests is committed to creating Tree Equity. By planting the right trees, the right way in the right place, we create healthier, climate-resilient communities for everyone. One way we do so is by participating in coalitions, such as the Extreme Heat Resilience Alliance, which is addressing the growing threat of extreme urban heat on vulnerable people worldwide.