Climate resilience: Copenhagen's dream of a flood-proof city

On July 2, 2011, the city of Copenhagen experienced what's now known as 'the storm of a thousand years'.

Within minutes, masses of water invaded streets and buildings, causing almost a billion euros worth of damage.

“We realised that year that Copenhagen was going to be hit by climate change, so we had the impacts analysed. It looks like we'll have up to 30% more rain, and a multiplication of rainstorms that will have a large-scale impact on the city,” explains Jan Rasmussen, Project Director of the City of Copenhagen's Climate adaptation plan.

The city has therefore launched a major plan to better manage the devastating downpours, known as cloudbursts, which are defined as rainfall of over 15 millimetres of in 30 minutes. The capital's « cloudburst management plan » consists of a series of small and large-scale solutions, both technical and nature-based, 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-kilometre-long tunnel that will link Copenhagen's inland lakes to the far end of the harbour. It is due to open in 2026.

“When we have a lot of rain that hits the city, we can fill up the tunnel using it as a reservoir, so when we have more room in our system, we can send it to the water treatment plant. In case of really heavy downpour, we can also empty the tunnel into the harbour and it will have a conveying function," explains Ditte Reinholdt Jensen, an expert in climate adaptation at HOFOR, the utility company in charge of these enormous projects.

The tunnel is estimated to cost 43 million euros. “What goes into constructing all of these, that is to be made up in the damages that we are preventing from