Citizens' preferences on green infrastructure practices and their enhancement in Portland, Oregon

Green infrastructure (GI) has been gaining increasing attention due to its efficiency in controlling and purifying urban stormwater runoff, creating environmental amenities, and biodiversity conservation. Nevertheless, the existing knowledge of people's preferences for GI is not yet sufficient for evidence-based policymaking for enhancing GI. This study analyzes citizens' perceptions of the relative importance of six GI practices and estimates their willingness to pay (WTP) to enhance them. To this end, the study applies two types of stated preference methods (best-worst scaling and contingent valuation) to citizen survey data collected in Portland, Oregon. We found that GI practices that are more likely to lead to private benefits (e.g., rain barrels, urban trees) received relatively higher ratings, whereas the ratings of practices that do not offer such benefits (e.g., bioswales, rain gardens) were relatively lower. However, the diversity of preferences was large, as the relative importance varied widely among respondents. Heterogeneous preferences were also found in terms of citizens' WTP for hypothetical GI enhancement. Our comparison of uniform and variable payment schemes revealed that variable payment outperformed uniform payment because of the significant variation in citizens' WTP. The difference was large when the annual household payment was small.