How Can Cities Successfully Transform into a Sponge City?
A newly developed residential neighborhood in Berlin Grünau has already implemented the sponge city concept. Photo: Richard Harnisch, IÖW
Sponge City principles have become integral to climate-resilient urban development. The question now is how to embed these principles in urban planning – and how the federal government can support that effort. A research project led by the Institute for Ecological Economy Research (IÖW) on behalf of the Federal Environment Agency (UBA) offers new insights into these questions. A fact sheet (DE) and a symposium held in June 2026 point to a clear conclusion: implementing more sponge cities requires financial, regulatory, and informational policy instruments to work together in an integrated way across all elements of the sociotechnical system – technologies, institutions, and actors alike. Cross-sectoral cooperation and policy decisions that have an impact at the administrative level are crucial. Equally important are considerations of social justice at every stage of the planning process.
Sponge City: Preparing for the Future in the Face of Climate Change
Climate change challenges cities and municipalities increasingly. Extreme weather events – heat waves and heavy rainfall – stress municipal infrastructure, disrupt urban ecosystems, and undermine public health and quality of life. The “sponge city” concept responds to these challenges and offers a model for integrated, forward-looking, climate-resilient urban development. The aim is a paradigm shift in urban water management: water should be stored, retained, allowed to infiltrate and evaporate, and reused. In this way, the sponge city is designed to protect against damage from heavy rainfall and drought, reduce heat stress, and stabilize groundwater reserves. Enhanced evaporation and infiltration, coupled with reduced surface runoff, strengthen urban ecosystems and ease pressure on sewer systems during intense rainfall events.
“The sponge city stands for water-sensitive, climate-resilient urban development,” says Dr. Alexandra Dehnhardt (IÖW), overall project manager for “Sponge City: Implementing Blue-Green Infrastructure”. “Blue-green infrastructure is key – particularly nature-based solutions such as green roofs and soil de-sealing. Many cities recognize the need and are implementing sponge city concepts, but implementation is especially challenging in existing urban areas, requiring cross-sectoral cooperation within city administrations and effective support for local governments.”
Fact Sheet: Recommendations for Building a Climate-Resilient Sponge City
Barriers rarely occur in isolation. A mandatory greening of roofs, for example, may stall not only because of a missing legal basis, but also due to limited public acceptance, unclear responsibilities, and a shortage of skilled professionals. That is why a coordinated mix of financial, regulatory, and informational instruments is needed – one that targets multiple elements of the system, updates the regulatory framework, mobilizes key actors, reflects on normative values, and advances relevant technologies.
In their fact sheet (DE), the researchers recommend the following policy mix for federal policymakers:
- Financial support should be continued and made more accessible to smaller, structurally weaker municipalities.
- Incentive instruments are needed to encourage private actors to implement measures on their own properties.
- Transdisciplinary research and innovation projects should be funded to close knowledge and data gaps, develop new technologies, and create flagship initiatives.
- Legal standards and requirements are necessary to establish binding frameworks for stormwater management and land use.
- Instruments for knowledge transfer and impact scaling are needed to enhance the visibility and effectiveness of the other policy tools.
Learning From Each Other: Sponge City Experts in Dialogue
At the expert symposium “Strengthening Sponge Cities – Designing Effective Federal Policy Instruments”, held at the German Environment Agency in June 2026, more than 60 participants from municipalities, academia, non-governmental organisations, and the private sector discussed the political, strategic, and communication frameworks needed to advance the transition to sponge cities. The discussion yielded three central demands: agencies should collaborate across departments to implement sponge city approaches successfully; equity considerations and the social impacts of deploying blue-green infrastructure should be integrated from the outset; and green roofs – a cornerstone of the sponge city – should be planned to maximize not only water retention but also synergies, for example by combining them with photovoltaic systems.
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