Decentralised green infrastructure: the importance of stakeholder behaviour in determining spatial and temporal outcomes

The traditional approaches to resolving urban stormwater problems include costly expansion of collections systems and/or creation of in-line storage and treatment capacity. An emerging ‘green’ infrastructure (GI) approach would instead reduce runoff sources. An agent-based model is used to explore the spatiotemporal emergence of rain gardens and green roofs in Point Breeze, a 175 ha neighbourhood in South Philadelphia, PA, under two different scenarios. In the first, household GI adoption rules consider only economic self-interest and the physical compatibility of each GI technology with lot characteristics. In the second scenario, the adoption rules are enhanced based on insights into the possible behaviour of property owners, as intuited by the designers/authors over a two-year period using a variety of empirical methods. In Scenario 2, relevant knowledge and perceptions are transferred to household decision-makers through social networks, and exposure to GI is assumed to diffuse GI innovation. The two scenarios differ in the temporal rate of GI adoption in the neighbourhood at large (greater in Scenario 1), as well as in the spatial influence of early adopters in Scenario 2, underscoring the importance of stakeholder decisions in the ultimate the effectiveness of watershed-scale GI programs.