Plant-covered roofs have become a regular sight in Portland, Oregon. The city is a leader in incorporating green infrastructure for stormwater management, including free street trees, rebates for small residential housing footprints, and green roofs.
Green roofs, also known as rooftop gardens or ecoroofs, typically have a layer of plants growing in soil on top of the roof, as well as material for waterproofing, structural support, and insulation. A new study from Reed College in collaboration with the University of Illinois and Portland State University explores the benefits of green roofs and how much Portland residents are willing to pay to increase the number of green roofs across the city.
For green roofs to reduce summer temperatures by less than 0.5 degrees, reduce sewer overflow by one, and increase pollinators by 50%, residents were willing to pay $202.40 per household or $54.4 million total for Portland.
“Countries around the world are investing significant public resources to reduce the impact of stormwater runoff,” explains Amy Ando, professor of agricultural and consumer economics at U of I, and a co-author on the study. “Green roofs are part of that solution because they capture some of the rain that would otherwise end up in sewage systems. Knowing the benefits from investing in green roofs is important for implementing sound public policies.”
The study investigates how much people would pay for benefits that include reduced sewer overflow events (CSOs), reduced urban heat island effect, and increased presence of pollinators like bees and butterflies. Like many cities, extreme rainfall events in Portland can quickly overwhelm old sewer systems and lead to flooding, which impacts water quality as well as transportation and properties.