In Portland, Oregon, roof coverings have become the norm. For stormwater management, the city is considered a leader as it incorporates green infrastructure, free street trees, green roofs, and discounts for small residential housing footprints.
Green roofs, also called rooftop gardens or eco-roofs, typically feature a layer of plants grown in the ground on the roof, along with structural support, waterproofing, and insulation materials. The benefits of green roofs and how much Portland residents are willing to pay to increase the city’s green roofs has been explored in a new study from Reed College in association with the University of Illinois and the University of Portland State.
Countries around the world are investing significant public resources to reduce the impact of stormwater runoff. Green roofs are part of this solution because they capture some of the rain that would otherwise end up in sewer systems. Knowing the benefits of investing in green roofs is important for implementing sound public policies.
Amy Ando, study co-author and professor of agricultural and consumer economics, University of Illinois
The research studies how much people would be willing to pay for benefits such as a decrease in the urban heat island effect, reduced sewer overflows (OSCs) and increased presence of pollinators, such as butterflies and bees. As with many cities, adverse rainfall in Portland can quickly overwhelm old sewer systems and lead to flooding, affecting water quality and possibly property and transportation.
Although CSO events have decreased significantly in Portland after a major system upgrade ($1.4 billion “Big Pipe Project”), they are still occurring. Our results show that survey respondents place the highest value on reducing CSO events and are willing to support additional funding for this.
Noelwah Netusil, Study Lead Author and Professor, Economics, Reed College
As of 2018, the City of Portland has required new downtown properties with a footprint of over 20,000 square feet with an eco-roof that covers 100% of the area (with some exceptions that include traffic lanes). evacuation and solar panels) to safeguard the city against flooding. Covering 1.4 million square feet, the majority of green roofs are concentrated in the center of the city.
Survey respondents specified how much they would pay for a green roof to arrive at a scale of benefits. For example, it will cost more to reduce sewer overflows three times a year instead of twice, lower air temperatures by more than a degree instead of half a degree, and bring in many more bees, birds and butterflies instead of keeping pollinators constant.
Respondents were willing to pay $442.40 per household for green roofs to reduce average temperatures by more than 1°F, reduce sewer overflows by three for a year, and increase pollinators by 150%. This represents $116.8 million for the city of Portland.
Residents were willing to pay $202.40 for each household or $54.4 million to Portland for green roofs to reduce summer temperatures by less than 0.5°F, reduce sewer overflow one and increase pollinators by 50%. The cost will be included in the monthly installments of their sewer and stormwater utility bill for one year. Green roofs would also be installed one year after the program was fully funded.
According to the survey, respondents who had seen or visited a green roof had the highest estimated willingness to fund the program. However, respondents who were unaware of green roofs prior to completing the survey were also supportive of the green roof program. Additionally, residents generally preferred that the green roofs be evenly distributed throughout the city instead of being concentrated in the downtown area.
The reduction in CSO events had the greatest value for all survey respondents, whether they had visited, seen, heard, or knew nothing about green roofs before responding to the survey. The total estimated benefits of the programs we examined would be sufficient to more than double the number of green roofs on commercial and industrial properties in our study area (Portland).
Noelwah Netusil, Study Lead Author and Professor, Economics, Reed College
University of Illinois extension and Illinois-Indiana Sea Grant water quality specialist Eliana Brown says the research results will be added to a new website on the green stormwater infrastructure.
Brown says:When Illinois municipalities contact us about building green infrastructure, they want to know how the public will benefit from their investment. This New Green Roof Research Goes Beyond Portland, Giving Stormwater Professionals More Tools to Advocate for Practices Helpful to Communities in Illinois and Beyond.”
The paper is published in Landscape and Urbanism, and study authors include Noelwah Netusil, Lauren Lavelle, Sahan Dissanayake, and Amy Ando.
The study was financially supported by the Bernard Goldhammer Fellowship for Economics and Natural Resources Research, Reed College, and the Stendal Fund for Economics, Reed College. This study also focuses in part on work supported by USDA-NIFA Multistate Research Grant W4133 1008843.
Journal reference:
Netusil, NR, et al. Promote the public benefits of green roofs. Landscape and Urbanism. doi.org/10.1016/j.landurbplan.2022.104426.
Source: https://illinois.edu/
