Cities/Roads
Copenhagen has built a series of reservoirs to store excess rainfall and wastewater, preventing the overflow of sewage systems and reducing the risk of flooding in the city. As well as providing greater protection, the reservoirs also improve the surrounding environment, with the water in the harbour now so clean that you can swim in it.
Located on the coast and with the Little Mermaid as its symbol, Copenhagen has a close relationship with water. Many residents experienced this affinity more strongly than ever in August 2010 when the Danish capital experienced some of the heaviest thunderstorms and rain in the last hundred years.
“Some areas had up to 140mm of rain in the space of a few hours,” says Lykke Leonardsen, Head of Strategy at the city council’s centre for parks and nature. “It was exceptional.”
The effect of such torrential rain put enormous pressure on the city’s drainage systems. “The system couldn’t handle that huge amount of water and there was localised flooding in some parts of the city,” Leonardsen explains. “Within four hours, some individual overflow outlets were releasing twice the normal amount of water that the whole system would normally release in a year.”
Changing conditions
It is likely that the city will experience similar conditions more often in future, with predictions that climate change will result in increasing periods of intense rain. There will generally be warmer summers with torrential downpours and wetter winters.
“It was a wake-up call, it showed that we face a big problem with regards to flooding,” Leonardsen adds. “Predictions are that whereas we used to experience such huge rains every 50-60 years we will get them every 20 years in future.” Estimates are that overall the city will receive around 30% more precipitation per year by the end of this century.
The city started taking action in the 1990s to deal with the threat of floods from heavy rains. “We wanted to reduce the levels of overflow into the sewage systems,” says Leonardsen. The solution was to build a network of temporary reservoirs to store the rainwater and then gradually release it into the drainage systems.
According to Leonardsen, the measures have improved the water quality dramatically in Copenhagen Harbour, so much so that in 2002 a series of swimming baths were opened.
“We showed that the protection efforts can also help improve the environment in the city and quality of life for residents,” says Leonardsen. However, she explains that more reservoirs will be needed in future to maintain the high standards achieved, along with other measures that are currently being planned to increase Copenhagen’s resilience to climate change.
Early action
The efforts demonstrate the Danish capital’s advanced thinking on tackling climate change. The city council agreed in 2009 to make Copenhagen CO2 neutral by 2025 as part of an ambitious climate change plan. As part of the plan, a comprehensive adaptation strategy is due to be released in 2011. The city’s is taking a long-term view that allows flexibility and targeted action where it can be most effective, says Leonardsen.
Other ways to reduce flooding risk are to increase the amount of vegetation throughout the city, including green walls and roofs, as well as creating a network of small ‘pocket parks’ – small green areas dotted throughout the city. Leonardsen explains that these help to slow rainfall run-off and reduce the risk of flooding, “We want to have water features throughout the city that will store the water.”
These green and blue areas will also help to cool down the city in summertime to cope with the higher temperatures expected in future as vegetation holds moisture and releases it into the air giving a cooling effect compared to concrete and other man-made surfaces that tend to absorb and retain heat. These areas will also increase recreation areas for residents and improve conditions for wildlife.
As well as improving the environment of the city and the quality of life, the measures are cost-effective, insists Leonardsen. “We estimated that to expand the sewage systems to cope with the expected extra quantities of water would have cost around €2 billion, whereas handling much more water on the surface as we are doing will cost around €0.75 billion.”
Leonardsen adds that the approach offers economic benefits for the city. “We could choose from various adaptation approaches. We favour the green one. In many ways, it’s the cheapest solution while being an investment in a more beautiful, healthier and better city.”
“We’re not just focusing on the obstacles that climate change gives us, we’re also focusing on the possibilities,” she says.