Sponge Cities
Context:
Urbanisation and climate change have intensified risks like sea-level rise, floods, and extreme heat, demanding adaptation efforts from governments.Nature-based solutions (NbS) are gaining global adoption, with China promoting sponge cities since 2014 to improve flood resilience.
About Sponge Cities:
Sponge cities are urban areas designed to absorb rainwater through natural spaces like trees, lakes, and parks. The concept focuses on enhancing “sponginess” to reduce flooding by utilising nature-based solutions such as greenery and improved drainage systems.
How Is ‘Sponginess’ Measured?
Sponginess is assessed by measuring the ratio of natural infrastructure (grass, trees, lakes) to built infrastructure (concrete, pavements). Soil texture and plant cover are also analysed to determine how much water the land can absorb.
Study Findings on Major Cities’ Sponginess
In a study of seven cities, Auckland ranked highest with a 35% sponge rating, while London ranked last with 22%, highlighting the impact of green spaces and natural drainage on urban flood resilience.
How Can Cities Increase Sponginess?
Cities can enhance sponginess by adding parks, trees, and natural drainage systems. Digital tools like AI-driven mapping can help plan optimal green space usage to mitigate floods and droughts.
Key Features of Sponge Cities:
- Green Spaces: These include parks, wetlands, and green rooftops that act as sponges, absorbing excess rainwater and providing natural habitats.
- Permeable Surfaces: Roads, pavements, and parking lots are designed using permeable materials, allowing water to infiltrate the ground rather than creating runoff.
- Water Storage Systems: Underground reservoirs, ponds, and tanks store rainwater for later use, reducing pressure on drainage systems and providing water during dry spells.
- Urban Wetlands: Integrated into parks, wetlands act as natural sponges to hold excess rainwater and enhance biodiversity.
Objectives of Sponge Cities
- Flood Mitigation: By absorbing and storing excess rainwater, sponge cities prevent flooding during heavy rainfall.
- Water Resource Management: Stored rainwater is used for irrigation, drinking, or industrial purposes, helping cities manage water shortages.
- Ecological Restoration and Improved Urban Living: Green spaces and wetlands not only absorb water but also restore ecosystems, improving biodiversity and air quality.
Urban Flooding in India: Guwahati Case Study
- Guwahati experiences frequent floods and droughts due to rapid urbanisation, poor drainage, and excessive cementing, which blocks natural water absorption.
- The sponge city concept, focusing on restoring natural water channels, green spaces, and permeable surfaces, could help address these issues.
Implementation in India
- Andhra Pradesh Initiative: Amaravati integrates sponge city features like green corridors, revived water bodies, and permeable pavements to manage floods and conserve water.
- Bengaluru’s Approach: Bengaluru has begun restoring lakes and using permeable surfaces in new developments, aiming to mitigate flooding and water scarcity, though more work is needed.
- For example, the revival of Kaikondrahalli Lake is a step toward adopting sponge city principles.
Global Examples of Sponge Cities
- China:Over 30 Chinese cities, including Wuhan and Shanghai, have adopted sponge city principles. Wuhan now manages 70% of its rainwater through green rooftops, permeable pavements, and water storage systems.
- Germany:Hamburg and Berlin integrate green roofs, rainwater harvesting, and natural water restoration in their urban planning, reducing flood risks and improving water management.
Importance of Sponge Cities in Flood Mitigation
- Rainwater Absorption and Retention: Sponge cities absorb rainwater through green spaces and permeable surfaces, reducing the risk of flash floods during heavy rains. Example: Singapore: The city’s “ABC Waters Programme”
- Natural Water Storage: By storing rainwater in natural and artificial reservoirs, sponge cities can mitigate the impact of water shortages and maintain a balanced water cycle.
- Enhanced Drainage Systems: Sponge cities employ enhanced drainage systems that are less reliant on artificial infrastructure, reducing the burden on traditional storm water systems.
- Climate Resilience: With climate change increasing the frequency and severity of floods, sponge cities enhance resilience by creating urban environments capable of adapting to both floods and droughts.
Challenges in Implementing Sponge Cities
- Lack of Awareness: In many regions, the understanding of sponge city benefits is limited, leading to insufficient policy support.
- Funding Issues: Low priority for sponge city and climate change adaptation planning and investments.
- Existing Infrastructure: Retrofitting existing urban areas with sponge city features is challenging, particularly in highly urbanised regions like Delhi and Mumbai, where space and infrastructure are already saturated.
Way Forward
- Public-Private Partnerships (PPP): Governments should encourage private investment through PPP models to finance sponge city projects, reducing the financial burden on local governments.
- Pilot Projects and Scaling Up: Vellore has initiated a pilot project to manage stormwater through green infrastructure, which could serve as a model for other Indian cities.
- Community Involvement: Indore has involved local communities in water conservation efforts by reviving lakes and ponds.
