Copenhagen was hit by a 1000-year storm (cloudburst) in 2011, creating a sense of urgency and momentum to prepare climate adaptation strategies. The Cloudburst Management Plan (CMP) was developed in 2012 as an offshoot of the city’s Climate Adaptation Plan (2011). The CMP includes more than 300 projects, with more than half of them being surface blue-green infrastructure measures, and others being traditional underground grey infrastructure.

The financial model is an innovative co-financing strategy that shares the main financial responsibilities between the municipality and HOFOR, the utility company. A legal change at the national level was lobbied for by the City of Copenhagen to allow utility companies to co-fund multifunctional surface solutions from water tariffs (user fees). Additionally, private property owners are responsible for stormwater management investments on their own properties. The new legal framework allows this co-financing by the utility company under strict conditions:

• Alternative blue-green infrastructure must be proven more cost efficient than traditional (grey infrastructure) solutions.
• Funding from water tariffs can only be used for purposes directly related to the handling of wastewater (stormwater management measures, the drainage system).
• Utilities are not allowed to propose or carry out alternative water projects on their own. They can only provide funding, but the projects must be initiated, in this case, by the municipality.

Although the entire implementation of the plan has been challenged by recent national changes in service level requirements, the CMP has been successful in facilitating a transition from traditional grey infrastructure only to climate adaptation through nature-based solutions. The success is explained by the strong partnerships between various actors, a strong business case that quantifies the cost-efficiency of naturebased solutions and having a long-term reliable funding source with the water tariffs.