Climate change has brought with it an increased frequency of extreme weather conditions. Two cities aware of this fact more than most are Copenhagen and New York.

In 2011, the skies above Danish capital Copenhagen burst, plunging the city into chaos as 15 centimetres of rain poured down in less than three hours. Residential properties, public transport systems and key roads were all inundated. The total cost of damage caused by the flooding was estimated to be around $1 billion.

A year later and more than 3,400 miles away, Hurricane Sandy swept through New York, resulting in coastal flooding that shook the Big Apple to its core. At least 43 people in the city lost their lives due to the effects of the storm, the total cost of destruction amassed some $32 billion.

Beleaguered and battered, the cities have emerged from their respective climatic crises equipped with plans to safeguard against similar events in the future. And now, to further boost their defences against the effects of climate change, the two cities are teaming up.

In New York, where the threat of torrential rain looms over the city, Copenhagen will offer guidance on cloudburst management. For its part, New York will inform its Danish counterpart about dealing with the threat of rising sea levels and coastal flooding – both very real dangers in Copenhagen.

Following the 2011 floods, Copenhagen developed its award winning Cloudburst Management Plan. This city-wide strategy combats surplus water supplies with under and over ground solutions.

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Below the city, Copenhagen’s sewer network is to be expanded. Up on deck meanwhile, dual usage systems will combine rainfall management and urban development. These innovative strategies include green streets, pocket parks and traditional playing fields – all of which will soak up the rain during heavy flooding.

With the cloudburst project fully implemented, it is estimated that the avoided environmental costs for Copenhagen will be around $290 million.

Across the pond, New York has carried out extensive work to defend against coastal flooding and rising sea levels since Hurricane Sandy struck five years ago. The city’s Green Infrastructure Program uses sustainable projects – such as rooftop gardens – to create natural stormwater management systems that are integrated within the surrounding urban environment.

The proposed green infrastructure will reduce runoff and flooding in New York and also have a natural filtration capacity to treat stormwater before the deluge is discharged into Jamaica Bay. The sustainable scheme also encourages community engagement via activities such as gardening and farming.

The symbiotic strategy between Copenhagen and New York should be mutually beneficial in a number of ways. By teaming up, the cities will have access to one another’s empirical research without having to experience first-hand the natural disasters from which they were collated.

In addition to the financial benefits that the collaboration could deliver, through their collective climate change resilience projects, Copenhagen and New York will be able to protect against loss of life and displaced populations.

From a wider perspective, the partnership demonstrates that the intercontinental sharing and development of innovative adaptation strategies is eminently possible. The project could pave the way for similar alliances in the future, with the potential to turn the tide on not just flooding but many other effects of climate change too.


Cities100 is a mission shared by Sustainia, C40 and Realdania to find the 100 leading city solutions to climate change. Read the 2016 publication, and follow the conversation online using #Cities100

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