Project type                    Urban sponge system project

Partners                          Izmir Metropolitan Municipality, Izmir Institute of Technology, Water Resources Management Research & Application Center

Beneficiaries                  Izmir residents, Izmir Metropolitan Municipality

Dates                                2022- Ongiong

Website                          Izmir Green City Action Plan

   Climate Neutral Future in Izmir

The Izmir Sponge City Project is an innovative urban initiative aimed at enhancing flood resilience through nature-based solutions. The project’s primary goal is to manage rainwater through natural processes that capture, store, and filter water as close as possible to where it falls. By reducing runoff and alleviating pressure on existing stormwater systems, these solutions minimize urban flooding risks.

Additionally, they mitigate the urban heat island effect, enhance biodiversity, and contribute to a cleaner environment by filtering pollutants from runoff water. The collected rainwater is repurposed for irrigation and household use, maximizing resource efficiency. Studies emphasize the project’s cost-effectiveness, showing that nature-based urban water management systems are 50% cheaper and 28% more efficient than traditional artificial systems.

To promote community involvement, Izmir’s municipality distributed 5,000 rainwater tanks to residents, each capable of saving up to 220 tons of water annually for non-potable uses like garden irrigation and cleaning. Additionally, the municipality provides support and encourages residents to create 10,000 rain gardens, which reduce flood risks, enhance urban biodiversity, and filter pollutants for cleaner water.

Related to this project, the study “Designing with ecosystem modelling: the sponge district application in Izmir” was conducted. Using the urban flood risk mitigation model of the Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST), developed within the Natural Capital Project, Izmir’s vulnerability to cloudburst flooding was assessed. The study identified high-risk districts, such as Karşıyaka, where over 50% of rainwater from a 70 mm rain event does not infiltrate, leading to significant runoff. A flood resilience master plan was developed for Karşıyaka, using digital ecosystem and flow accumulation models as foundational layers. A stepwise design process incorporated site-specific nature-based solutions (e.g., green infrastructure) to create a performance-based flood resilience strategy. This approach bridged the gap between spatial modelling insights and practical urban planning decisions. After implementing the interventions, the model was rerun, revealing a 58% increase in runoff retention within the redesigned district, validating the sponge district concept’s effectiveness. The study demonstrated that such performance-based flooding solutions using nature-based interventions are replicable in other cities vulnerable to cloudburst flooding.

• Increase in runoff retention: the redesigned sponge district has achieved a 58% increase in the retention of rainwater runoff, significantly improving flood management.
• Substantial domestic water savings thanks to the 5,000 rainwater tanks distributed to residents, which have the capacity to save up to 220 tons of water per year.
• Support to create 10,000 domestic rain gardens, which reduce flood risks, enhance urban biodiversity, and filter pollutants for cleaner water.