Resilient Cities Don’t Fear Rainy Days

Lykke Leonardsen is constantly thinking about rainy days… even when it’s sunny outside.

But you really can’t blame her.

Ever since Copenhagen’s 100-year storm on July 2 of 2011,  which caused major flooding and extensive infrastructure damage, city officials such as Leonardsen, who heads Copenhagen’s program for Resilient and Sustainable City Solutions, have been preoccupied with getting ready for that ‘next major storm’.

And with her knowledge and experience gleaned from overseeing the creation of a comprehensive Storm Surge Plan as well as a long term Climate Adaptation Plan, it’s appropriate that Leonardsen is also actively involved with ICLEI’s program committee for the 2019 Resilient Cities conference that takes place June 26-28 in Bonn.

When asked to describe Copenhagen’s biggest environmental threat in the short term, Leonardsen answers with a single word… precipitation. “I would say it’s the most immediate threat. Not necessarily the biggest threat – because if you look down the line at sea levels rising, it could be a huge issue for our city,” she observes.

Sandwiched between the twin threats of unprecedented weather systems and the prospect of rising seas, Leonardsen has another word that’s top of mind… resilience. A concept she sees as central to the upcoming event in Bonn. “It’s really important that we remain focussed on resilience” says Leonardsen. “City participation (at the conference) is really important. Cities talking about their challenges and solutions have a much bigger score for me than hearing from a consultant or an academic.”

Certainly Copenhagen has learned a lot since that devastating storm in 2011 when huge volumes of rain came down. According to the Danish Meteorological Institute, a cloudburst is defined as 15 mm of rainfall within 30 minutes. On that fateful day the Botanical Gardens meteorological station recorded 135.4 mm of rain within two hours. And at other locations, 4.5 mm within 60 seconds and 31 mm within 10 minutes and 63 mm within 30 minutes.

Overall, 80,000 homes were affected of which 10,000 homes had no electricity for 12 hours and 50,000 homes had no heating for an entire week, with overall damage from the storm estimated at 1 billion Euro.

In the wake of this disaster, Copenhagen fast-tracked the Cloudburst Management Plan, which has garnished the attention of other municipal leaders from around the world due to its frankness in terms of challenges and creativity tied to solutions.

The plan pulls no punches in stating that “Copenhagen’s sewage system lacks sufficient capacity to handle extreme rainfall events.” Rather than a ‘gray solution’ involving augmenting the existing sewage system and burdening taxpayers with untold billions more in taxes, the plan takes a more creative approach to flooding mitigation whereby it recommends that “water is led out to sea via roads, canals/urban waterways, and subterranean tunnels” and “the preferred solution will be drainage out to the sea via new flow routes.”

“We realized (when the plan was created) it wouldn’t be possible to manage heavy rainfall by expanding the existing system. It would be too expensive and too disruptive,” Leonardsen recalls. “So we basically began building new infrastructure in the city – mainly surface solutions, that would cost between one-half and one-third of a traditional water management solution (tied to the sewage system).”

One particularly innovative surface infrastructure change has been to fast-track the creation of a network of convex roads, designed to funnel water to parks and other catchment areas and eventually out to sea, rather than draining into the sewage system.

Other steps include expanding neighborhood green space, including pocket parks, throughout the city, which provide increased recreation areas for residents, serve as a place to direct heavy rainfall during storms and help to offset the heat sink effect that cities around the world are dealing with more frequently due to climate change.

Dubbed the ‘green and blue’ solution, Copenhagen’s Cloudburst Management Plan consists of over 300 projects and Leonardsen says the key to the success of this plan is that the projects are interconnected. “It’s a plan that covers the entire city that’s being implemented over 20 years, all tied to effectively managing 100-year storms,” says Leonardsen.

And what piece of advice can Leonardsen offer other cities, based on what Copenhagen has learned so far, now that their flood mitigation efforts are well underway? Number one she says is: make a plan. One that ties all the projects together, as opposed to a series of initiatives that may or may not complement one another. A plan that’s also detailed to the point where it drills down to the street level. “If you know this street will be able to handle so much water in a given situation, then you can work on what to do to improve each street.”

Even if cities don’t have the budget to carry through with a flood mitigation plan all at once Leonardsen says there is an opportunity to get things done bit by bit in her words. “If you’re renovating a street, you can incorporate stormwater management solutions at the same time. And slowly, slowly, the city will meet the standards it needs in order to manage heavy rains.”

As with past ICLEI events she has attended, at this year’s Resilient Cities conference in Bonn, Leonardsen says she is looking forward to learning from some of the multiple challenges other cities are facing when it comes to urban resilience. “We’ve learned a lot about risk assessment, mostly from what other cities are doing to tackle various problems. But it’s not like we go home and say ok they’re doing this here, let’s do the same thing in Copenhagen. It’s more about looking at some of  the elements of what other cities are doing, and then translating those things into a local context.”