Sponge cities, also known as “sponge city initiatives” or “sponge urban planning,” are an innovative approach to urban development and sustainable urban design, primarily aimed at addressing and mitigating urban flooding and water management issues. These initiatives are becoming increasingly important as urbanization and climate change contribute to more frequent and severe floods in many cities around the world. Developed to handle Monsoon type rainfall, they are being looked at to manage the heavy rainfall being caused by climate change.

The term “sponge cities” is used to describe urban areas with abundant natural areas such as trees, lakes, and parks or other good design intended to absorb rain and prevent flooding¹. They are designed to absorb rainwater and prevent flooding by using nature-based solutions¹. Cities as diverse as Shanghai, New York, and Cardiff are embracing their “sponginess” through inner-city gardens, improved river drainage, and plant-edged sidewalks¹. The concept of sponge cities has gained popularity in recent years due to the growing number of urban areas experiencing devastating floods caused by climate change¹.

The concept of sponge cities was proposed by Chinese researchers in the early 2000s and accepted by the Chinese Communist Party (CCP) and the State Council as an urbanism policy in 2014². Sponge cities are a new urban construction model for flood management, strengthening ecological infrastructure, and drainage systems².

Sponge cities matter because they can help prevent flooding in urban areas. They can also hold more water in rivers, greenery, and soil instead of losing it to evaporation, making them more resilient to drought¹. Natural ways to absorb urban water are about 50% more affordable than man-made solutions and are 28% more effective¹.

Researchers at Arup measured how much of seven major cities was covered by ‘blue and green infrastructure’ including grass, trees, ponds, and lakes. They also looked at the type and texture of urban soil to assess how much water it could hold. They used satellite imagery, artificial intelligence, and machine learning to make the calculations¹.

The concept of a sponge city is based on the idea of making urban areas act like sponges that can absorb, store, and manage rainwater instead of allowing it to flow directly into storm drains and overwhelm drainage systems. The key elements and strategies of sponge cities typically include:

Permeable Surfaces: Incorporating permeable pavements, roads, and sidewalks that allow rainwater to infiltrate into the ground, reducing surface runoff. Green Infrastructure: Increasing the presence of green spaces, parks, and urban vegetation to absorb rainwater, improve soil permeability, and provide natural drainage.

1. Rainwater Harvesting: Collecting and storing rainwater for various purposes, such as irrigation, flushing toilets, or groundwater recharge.
2. Flood Management: Developing sustainable flood management systems, including the creation of detention basins, wetlands, and green roofs to slow down and store rainwater during heavy rainfall events.
3. Water Recycling: Treating and reusing wastewater for non-potable purposes like landscape irrigation, industrial processes, or toilet flushing.
4. Improved Drainage Systems: Upgrading and expanding drainage infrastructure to handle excess water more efficiently, often through smart and technology-driven solutions.
5. Urban Planning and Zoning: Implementing urban planning and zoning regulations that prioritize water management, green spaces, and sustainable development.
6. Public Awareness and Education: Educating the public about water conservation, responsible water use, and the benefits of sponge city initiatives.

The concept of sponge cities has gained traction in countries like China, where rapid urbanization and frequent flooding have prompted extensive investment in these approaches. For instance, several Chinese cities, including Shanghai and Wuhan, have adopted sponge city programs to improve water resilience and reduce the impact of floods.

Sponge city initiatives aim not only to address flooding but also to enhance urban livability, promote environmental sustainability, and create more resilient and adaptive cities in the face of climate change challenges. These efforts align with broader goals of urban sustainability and ecosystem-based approaches to urban planning.