The Danish capital is bracing for an increase in torrential rains in the coming decades due to climate change. Huge infrastructures are being built both above and below ground to make the city more resilient to heavy rains.
On July 2, 2011, the city of Copenhagen suffered the “thousand-year storm.” Within minutes, masses of water invaded streets and buildings, causing almost a billion euros worth of damage.
“That year we realized that Copenhagen was going to be affected by climate change, so we analyzed the impacts. It looks like we will have up to 30% more rain and an increase in storms, which will have a large-scale impact in the city,” explains Jan Rasmussen, project manager of the city of Copenhagen’s climate adaptation plan.
Therefore, the city has launched a major plan to better manage devastating downpours, known as “Cloudburst”, which is defined as more than 15 millimeters of rain in 30 minutes. The capital’s “heavy rain management plan” consists of a series of small and large-scale solutions, both technical and natural, above and below ground.
To increase the water capacity of its system, the city has launched the construction of several tunnels under the city. We visited a 1.3 kilometer long tunnel that will link Copenhagen’s inland lakes with the far end of the port. Its inauguration is scheduled for 2026.
“When the rain hits the city, we can fill the tunnel using it as a reservoir, so that when we have more space in our system, we can send it to the water treatment plant. “In case of heavy rain, we can also empty the tunnel to the port and will have a transportation function,” explains Ditte Reinholdt Jensen, climate adaptation expert at HOFOR, the service company in charge of these pharaonic projects.
It is estimated that the cost of the tunnel will be 43 million euros. “What it takes to build all this is offset by the damage we prevent from occurring,” Ditte emphasizes.
Another tunnel, built in the Valby district, has already proven effective during smaller torrential rains on August 4, 2024, according to HOFOR.
Use the city surface to manage water
Other above-ground solutions are also being tested, such as building rain gardens in residential areas. A more permeable asphalt has also been tested to prevent water from remaining on the surface.
Some parks have been completely remodeled to cope with the stormy weather. The historic Enghavepark, built almost a century ago, has been completely redesigned to become a 22,600 m3 water reservoir, the equivalent of eight Olympic swimming pools.
The project is the result of extensive studies on the flow of water through the different districts of the city. The park is located downstream from the Carlsberg district, on a hill that can store 3,000 m3 of water. In the event of an overflow, the water will be discharged downstream to this park.
“First, the water will go down to this football field and then it will start going down to the lake. Finally, it will reach the rose garden. “If we need to store more water, the park gates will close and the entire park will fill with water.” , explains Jan Rasmussen in front of the concrete wall just under a meter high that surrounds the entire park.
With its historic lake, soccer field and gardens, the site does not look like anti-flood infrastructure, say the project promoters. “When we talked to the city architects about this project, we told them that this park should remain an integral part of the city. They said, ‘Wow, are you sure we can do this?’ And we did. “This park doesn’t look like a water reservoir,” adds Rasmussen.
The water stored beneath the Enghavepark can be used to power a pump used by the city’s street cleaning workers. “We also expect more heat waves, so we are trying to combine all this into one plan,” explains Jan, according to whom the Danish capital is cooperating with other cities to share their experiences on climate adaptation, through C40 and other organizations. .
“The work we are doing does not mean we can relax now. “It is going to take continued effort to be able to cope with all the rains we will see in the future,” confirms Ditte Reinholdt Jensen of HOFOR.
Towards a more systemic approach
Cities need to do more to protect themselves from climate risks and invest in urban social resilience, according to the European Environment Agency (EEA), which published its 2024 report on urban adaptation for climate resilience in April.
“Many of the actions carried out today are still project-based. We need to make them more systemic. “It is a big challenge for cities, but over time much more will be needed,” according to Wouter Vanneuville, adaptation expert to climate change by the EEA, which asks cities to multiply green spaces to counteract the inherent impermeability of cities, but also to keep water in cities, in the form of fountains and canals.
According to the EEA, in the last decade, 2021, 2022 and 2023 were among the five years with the highest economic losses due to extreme weather events, mainly floods.
“There is a lot happening on the ground. For several years, the largest cities have been developing and implementing plans, but now is also the time for smaller cities to do so, which do not have the resources to have a specialized team. “Many things are being done, but there is still much to do,” concludes the EEA expert.
