Europe’s sponge cities are turning rain from waste into a valuable resource

The EU is creating a ‘Sponge Facility’ to help implement nature-based projects that aim to make cities less prone to droughts and floods. Wild weather swings have turned water into a dual threat for Europe’s cities. When storms hit, there’s too much of it. When droughts come, there’s too little. But some experts believe that the ‘sponge city’ model – a nature-based approach to urban planning pioneered in China two decades ago – could help cities put a new spin on the old saying ‘save for a rainy day’. The model involves retrofitting urban areas with green spaces, permeable surfaces and water storage systems to absorb, retain and reuse rain rather than letting it drain away. This eases pressure on drainage systems and conserves water to use during dry spells. “One of the most impactful ways cities can adapt is by reversing a century of urban design that treated rainfall as waste rather than as a valuable resource,” says Justin Abbott, fellow and Europe water leader at engineering consultancy Arup. What is a ‘sponge city’? The sponge city model was developed in the early 2000s by Chinese landscape architect Kongjian Yu. He proposed using features such as ponds, wetlands and planted drainage channels to catch rainfall before it rushed into sewers and rivers. Slowing the runoff would reduce flood risk during storms, he argued, while rainwater could be used to replenish groundwater supplies or irrigate parks during dry spells. The greenery would also help cool city streets during heatwaves, and in some cases, healthy soil and wetlands could help protect against wildfires. After catastrophic flooding killed 79 people in Beijing in 2012, his ideas gained greater attention. In 2014, China adopted national guidelines for sponge city development, and the next year the country launched a 16-city pilot programme, including Wuhan, Xiamen and Chongqing. Another 14 cities, including Shanghai and Shenzhen, were added in 2016. By 2030, China now aims to have 80 per cent of its built-up urban areas function as sponge cities. Could sponge cities make Europe more resilient? Europe has been experimenting with similar water management projects for decades. Between 1998 and 2002, the southern Swedish city Malmö transformed its flood-prone Augustenborg neighbourhood by installing green roofs, wetlands, retention ponds and six kilometres of water channels. During major storms in 2007 and 2014, it suffered much less flood damage than other neighbourhoods. In the Netherland’s Rotterdam, the Benthemplein water square – opened in 2013 – doubles as a basketball court and recreational space in good weather, but during heavy rains, its three basins temporarily hold up to 1.7 million litres of water. Opened one year later in Denmark, Copenhagen’s Tåsinge Plads collects water from nearby rooftops using underground storage and rain gardens – shallow, planted areas that allow rain to soak into the soil. The European Commission hopes to expand projects like these across the continent. Its 2025 Water Resilience Strategy called for more sponge cities, as well as to restore more wetlands, and now the bloc is developing a ‘Sponge Facility’ to help develop them. The changes won’t necessarily be easy. Protected buildings, crowded streets and buried utilities make it difficult to retrofit historic city centres. But Abbott says that’s no excuse for failing to think outside the box. “These challenges should encourage better targeting, not inaction,” he says, suggesting smaller interventions such as removing courtyard paving, planting more trees and installing green roofs partially or completely covered with vegetation. Sponge cities are a ‘powerful’ tool but not a fix-all Even the greenest city can only absorb so much rain, though. During extreme storms, soil becomes saturated and storage systems fill up, leaving excess water nowhere to go. The catastrophic floods around Valencia in 2024 revealed the tragic consequences that can occur when extreme rainfall overwhelms a city’s defences like this. “Sponge measures are powerful, but they cannot address every challenge independently,” Abbott explains. Cities also need conventional drainage systems, larger reservoirs and designated routes that can carry floodwater away when rain gardens and wetlands reach capacity, he says. That’s a matter of more than engineering. Abbott argues that city authorities, water utilities, developers and landowners all have a responsibility to manage rainfall. Decisions made by one entity, he explains, can affect entire neighbourhoods. “In planning and designing cities, we need to put water first,” he says. “We need to ‘design with water’.”