As rain falls violently from the sky, city streets begin to more closely resemble streams and lakes than the typical concrete desert adorned with scorching sidewalks. As climate change intensifies both storms and temperature, urban areas are becoming hostile environments. While the issue of flooding and extreme heat are very different, they share a common cause and surprising solution.
A rising trend when addressing climate change in cities is focusing not on what’s built at street level, but what exists above it. Rooftops in cities act as radiators, absorbing the sun’s rays and storing heat effectively warming the entire building and the surrounding air. At the same time, they also contribute to stormwater runoff, overwhelming drainage systems during times of heavy rainfall. Green roofs, partly or entirely covered with vegetation, offer a promising solution. In addition to their visual appeal, green roofs help reduce flooding, lower temperatures, reintroduce nature to urban spaces, and improve overall public health.
Despite these benefits, cities argue that mandating green infrastructure would place an unequal financial burden on developers. Installation costs range from $15 to $40 per square foot depending on the type of green roof and there is continuous maintenance cost. However, this concern overlooks the long-term economic and environmental benefits. In order to make green roofs more accessible, some local governments have offset upfront costs through tax credits and grants.
Cities that have already implemented green roof policies demonstrate that it is both feasible and effective. Toronto for example became the first North American city to adopt a green roof bylaw in 2010, mandating them on new large buildings. Since then, millions of square feet of greenery has been installed and is currently aiding in reducing flooding and high temperatures. Copenhagen has also introduced similar policies as a part of their broader climate adaptation strategies. These examples directly counter the idea that green roofs are impractical and show that large-scale implementation is both achievable and beneficial.
One of the most immediate benefits of green roofs is their ability to absorb storm water. Traditional impervious roofs result in storm water rushing off almost instantly which contributes to overwhelmed sewer systems. Green roofs absorb and retain rainwater through vegetation and soil. According to Green Roofs for Healthy Cities, green roofs can be successful in catching a significant amount of precipitation and in cities with aging infrastructure this is especially important to avoid flooding. In some cases, green roofs can retain up to 70-90% of rainfall during summer months, significantly easing pressure on city systems and reducing the risk of sewage flooding into nearby waterways.
This infrastructure also plays a significant role in reducing the urban heat island effect. This is when cities experience temperatures of up to 7 degrees Fahrenheit warmer than surrounding rural areas due to the abundance of heat absorbing materials such as asphalt and concrete. According to the U.S. Department of Energy, rooftop temperatures on an extremely warm day can reach above 150 degrees Fahrenheit. This contributes to the increase of air temperature and the need for energy in buildings to operate cooling mechanisms.
Green roofs solve this problem by remaining generally cooler as the space covered by vegetation reflects sunlight rather than absorbing it and also releases moisture through evapotranspiration. This results in the surface temperature decreasing by 56 degrees and the internal building temperature by 27 degrees. By lowering rooftop and surrounding area temperatures green roofs would aid in reducing heat related illness, decrease energy demands for air conditioning, and make cities overall more livable. Studies from the Environmental Protection Agency show that they also contribute to improved air quality by filtering pollutants and capturing particulate matter, which is especially important in densely populated urban areas where respiratory related illnesses are more common.
Cities have prioritized efficiency and density over human health for far too long. Green roofs offer the chance to reintroduce nature into spaces that it has seemingly been erased. As towns and cities across the country update building codes and climate resilience plans, they face a critical opportunity and the choices made today will have lasting impacts for years to come. Cities should follow the example set by Copenhagen and Toronto, mandating green roof policies on new infrastructure and offering subsidies to curb installation costs because green roofs not only impact those in the building, but also the entire city as a whole.
Stella McHugh lives in Northampton.