Copenhagen weather change prompts audacious flood plan

Copenhagen is one of many cities threatened by rising sea levels and extreme weather – but it has an ambitious plan to defend itself

  • By Sandra Kilhof | Friday, October 3rd, 2014

An artist’s impression of how urban areas in Copenhagen will be converted to store water during heavy downpours. The cost of installing new drains throughout Copenhagen is estimated to be $1.73-2.6bn

The devastation caused by freak weather phenomena such as Typhoon Haiyan and Hurricane Sandy has made authorities focus on the urgency of improving climate resiliency in major coastal and low-lying cities. With communities exposed to the fury of extreme weather and rising seas, officials are faced with the task of overhauling centuries-old infrastructure. Many have, up until now, assumed our sewers and technological developments would be enough to keep urban populations safe from extreme weather. But, as recent years’ catastrophic weather has proven, the majority of cities are in need of serious upgrades.

On July 2, 2011, a cloudburst inundated Denmark’s capital, Copenhagen, with 135mm of rain in less than three hours, flooding basements, streets and major roads. According to the City of Copenhagen, the deluge caused $1.04bn worth of damage. To make matters worse, the downpour came less than a year after a similar cloudburst flooded a large part of Copenhagen’s suburbs and caused irreversible damage to homes and infrastructure.

The experiences have left a mark, with 45 percent of Danes fearing damage from future downpours, and 61 percent of Copenhageners having experienced water damage to their property. Having witnessed millions of dollars’ worth of cars, shop contents and personal effects float around in lakes of sewage water – formed by the city’s low-lying roads, parks and pavements – Danish politicians have been forced to address one of the world’s major challenges: climate change and the havoc it could wreak on our way of life.

Sewers are normally not visible, but that will change – Lykke Leonardsen, Head of the City of Copenhagen’s Climate Unit

Climate management
The City of Copenhagen created a Climate Adaptation Plan, which will bolster the city’s defences against water, wind and temperature. “We know Copenhagen is going to experience climate changes and we conducted a series of studies that could give us an overview of the impact they will have on our city,” says Lykke Leonardsen, Head of the City of Copenhagen’s Climate Unit. “We did a risk assessment so we could match our city’s development with a plan to handle these issues.”

The intense flooding in 2011 prompted the city’s politicians and authorities to approve a cloudburst management plan, which, together with a water catchment plan, makes up the main part of the climate adaption strategy. Changes will include the building of dikes and making management of storm water more localised. There will also be warning systems for rain, and waterproof cellars, while urban areas will be adapted to store rainwater with minimal damage.

“The water catchment plans have been subject to public hearings because, in some areas, we’re creating water boulevards that can carry water away when there’s excess rain,” says Leonardsen. “We’re putting in a new layer of infrastructure and changing the way the city looks. For instance, sewers are normally not visible, but that will change, and obviously we needed to discuss that with the local community.”

As part of the plan, Copenhagen will be supplementing existing sewers with an overground water system that combines landscape architecture with water boulevards, and massive water storage in parks and football fields when necessary.

“We don’t want to fill up our sewers with rainwater and we need to keep dirty, polluted water in the sewerage system,” says Leonardsen. “By leading water into lakes, streams or the harbour, we’re trying to delay the flood and make sure the water above ground is clean. We had one fatality as a result of the cloudburst in 2011 and it was caused by a disease stemming from rat urine in the sewage water that had reached our cellars and roads. This is why it’s necessary for us to implement a citywide cloudburst management system.”

The downpours that flooded Copenhagen in recent summers are likely to be repeated across Europe. Meteorologists expect precipitation will increase 25 to 55 percent in the winter, and summer downpours will be 30 to 40 percent heavier and spaced further apart. Current sewers cannot meet such future increases in water, and storm surges from the sea are a growing threat for coastal cities such as Rotterdam, Hamburg and New York. The Copenhagen City Council has therefore decreed the new infrastructure must limit floods to an average of once every 10 years.

$1.04bn

Damage to Copenhagen from a single storm in 2011

Learning lessons
The cost of installing new drains throughout Copenhagen is estimated to be $1.73-2.6bn, and an additional $521-868m to separate rain and wastewater in individual dwellings. For this reason, planners have recommended managing rainwater locally instead of guiding it to sewers. The estimated investment for the overground solution is $868m and includes simple measures such as replacing concrete or tiles in courtyards and squares with grass and trees. Without action, damage to buildings and infrastructure, combined with lost earnings from storm surges and floods, could total as much as $3.5bn over the next 100 years.

“What we’re adapting to is something that happens every 10 years now, but will become an annual event in the future,” says Leonardsen. “The frequency and intensity of cloudbursts will only go up, and we need to spare the city from a lot of costs and damages related to that. We can’t gauge how bad future climate change will be, so we need flexible solutions for an unknown future.”

Leonardsen adds other cities can learn from them: “Study what happened to Copenhagen during the cloudburst or New York during Hurricane Sandy. You think your city is well functioning, but it is actually quite vulnerable to climate change and life can quickly grind to a halt.”

Copenhagen’s green development system to manage water is the first to incorporate an entire city. It will take up to 30 years to implement all the measures outlined, but it is clear this is an investment worth making. It will not only secure the city for years to come, but also provide its inhabitants with a slew of green, open spaces.