The project “Sponge City: Implementing blue-green infrastructures“ has examined how the transition to climate-resilient and water-sensitive cities can be achieved, and which policy instruments can support local authorities on this path. This fact sheet presents the key conclusions. Against the backdrop of growing challenges posed by heat, water scarcity and heavy rainfall, a core principle of the Sponge City concept is to retain, store, allow to trickle away or utilize rainwater locally wherever possible, thereby restoring the natural water cycle to a greater extent. The three objectives of the Sponge City concept are: 

• Climate adaptation, to reduce damage caused by extreme weather events and improve the quality of life in cities.
• Moving closer to the natural water balance, to enhance evaporation, groundwater regeneration and the functions of urban ecosystems.
• Relieving pressure on the sewer system, so that rainwater does not lead to flooding during heavy rainfall. 

Key elements of the sponge city are blue-green infrastructure such as unsealing, green roofs and facades, rainwater retention facilities and infiltration systems.

The transformation into a sponge city is not merely a technical task, but also requires societal and institutional change. The project has therefore analyzed the interactions between technologies, actors, and institutions as a so-called sociotechnical system. Key barriers to implementation include a lack of knowledge, insufficient financial and human resources, rigid administrative structures, a lack of cooperation between stakeholders, land-use conflicts and a low level of engagement from private property owners.

The project team examined 26 policy instruments that might support the transition to a sponge city, assessing their potential for effectiveness and transformation. The results show that funding programs for municipalities and the legal anchoring of blue-green infrastructure in urban and building planning are particularly effective. Furthermore, economic incentives for private actors, support for transdisciplinary research and innovation projects, and the legal recognition of rainwater as a valuable resource hold great transformative potential.

The key conclusion is that individual instruments are not sufficient. Instead, the project recommends a coordinated mix of instruments that combines financial support, incentive schemes, legal requirements, and knowledge-sharing and transfer initiatives. Particular synergies arise when funding programs are supported by standards and regulations, research generates new solutions, and information services support implementation. In this way, multiple barriers can be addressed simultaneously and lasting changes across the entire system can be initiated. The path to a climate-resilient sponge city requires, in particular, long-term political strategies, sufficient resources, continuous evaluations and anadaptive policy mix.

View Fact Sheet (DE)