Opening up the black box of polycentricity: a comparative study of blue-green infrastructure implementation as networks of action situations

Urbanisation and climate change require cities in North-West Europe to rethink water infrastructure. While blue-green infrastructure (BGI), including nature-based solutions, has high potential, implementation is challenged by diverse actors interacting and making decisions in different configurations and contexts, characteristic of polycentric governance. While research on BGI is expanding, these complex multi-actor interactions at the local, operational level remain poorly understood. To better understand how polycentric configurations unfold, this paper uses the concept of Network of Action Situations (NAS). We examine how contextual factors and linkages between action situations (biophysical, institutional, informational, and actor-related) influence the outcomes of BGI projects in Brussels, Belgium, and in Enschede, the Netherlands. Findings show that outcomes depend more on the quality than the quantity of linkages across Action Situations. Contextual factors strongly influence both linkages and results. Strengthening formal institutional and informational linkages emerges as particularly critical for effective BGI implementation.