Amy W. Ando and Noelwah R. Netusil
Green stormwater infrastructure (GSI), a decentralized approach for managing stormwater that uses natural systems or engineered systems mimicking the natural environment, is being adopted by cities around the world to manage stormwater runoff. The primary benefits of such systems include reduced flooding and improved water quality. GSI projects, such as green roofs, urban tree planting, rain gardens and bioswales, rain barrels, and green streets may also generate cobenefits such as aesthetic improvement, reduced net CO2 emissions, reduced air pollution, and habitat improvement. GSI adoption has been fueled by the promise of environmental benefits along with evidence that GSI is a cost-effective stormwater management strategy, and methods have been developed by economists to quantify those benefits to support GSI planning and policy efforts. A body of multidisciplinary research has quantified significant net benefits from GSI, with particularly robust evidence regarding green roofs, urban trees, and green streets. While many GSI projects generate positive benefits through ecosystem service provision, those benefits can vary with details of the location and the type and scale of GSI installation. Previous work reveals several pitfalls in estimating the benefits of GSI that scientists should avoid, such as double counting values, counting transfer payments as benefits, and using values for benefits like avoided carbon emissions that are biased. Important gaps remain in current knowledge regarding the benefits of GSI, including benefit estimates for some types of GSI elements and outcomes, understanding how GSI benefits last over time, and the distribution of GSI benefits among different groups in urban areas.