How Copenhagen Became a ‘Sponge City’

Over the last decade and a half, Copenhagen has adapted its infrastructure to a wetter future, overhauling critical components of its urban design and infrastructure to transform itself into a “sponge city,” writes Paul Hockenos in a piece in Yale Environment 360.

The city’s plan, known as the Cloudburst project, is partly a response to severe flooding in 2011 that caused $1.8 billion in damages. “This state-of-the-art defense system — which combines nature-based surface features, like wetlands and parks, with large underground structures, like storage pipes and retention basins — is expected to fortify the city against cloudbursts and sea level rise for 100 years.”

As Hockenos explains, “Although the Cloudburst project, which was originally slated to be completed in 2032, is less than halfway to its goal, experts say that Copenhagen is already in significantly better shape to withstand torrential rains.” The city has reduced its flood risk by 30 to 50 percent in the highest-risk areas.

The city’s strategy combines green infrastructure that filters and absorbs stormwater with gray infrastructure such as underground tunnels, basins, and pumping stations to manage excess stormwater. “Although Copenhagen’s architects say that urban flooding is the city’s foremost concern, the sponge city model offers advantages in times of aridity, too. The city’s green spaces, which detain water, help to replenish the city’s aquifers, and its tunnels, which hold rainwater from moderate-size storms, function as reservoirs that can be tapped during dry spells.”