Green roofs can help cool cities in the summer heat, but building them is only the first step. Many don't survive

This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: As summer temperatures soar across the United States and Europe, cities are being forced to confront the difficult reality that they're getting dangerously hot. Record-breaking heat waves strain power grids, send people to cooling shelters and can make the top floors of some apartment buildings unlivable.

One way to help cool buildings is to install green roofs—living rooftops covered by plants that can transform heat-absorbing rooftops into cooling solutions. Green roofs have long been promoted as a method to help cities stay cool. Cities often offer developers incentives to install them.

But just building a green roof isn't enough. Our research shows that what happens after a green roof is built is as important as the decision to install a green roof in the first place. We found that many green roofs are neglected and don't survive beyond a few years, likely because of maintenance costs.

When buildings' operational budgets are cut, landscape elements—including green roofs—are often altered or maintenance is scaled back to save money. Unlike a traditional roof made of asphalt, metal or tiles, a green roof is made up of layers, including insulation, waterproofing and drainage, that allow plants to grow atop the building. Depending on their design, these roofs can support everything from low-growing sedums to shrubs and trees.

Rockefeller Center's rooftop terrace gardens in New York City were designed in the 1930s to hold trees, grass, shrubs and seating areas, providing parklike respites far above the traffic. The roof of the California Academy of Sciences in San Francisco is fully covered by 2.5 acres (1 hectare) of wildflowers, succulents and other native coastal flowers. These roofs are more than just decorative landscaping.

Plants absorb sunlight that would otherwise heat up the building below. They also cool the surrounding air through a process called evapotranspiration, in which they release water vapor. Additionally, they can reduce the amount of energy needed for heating and cooling buildings by acting as insulation.