As record-breaking rainfall causes havoc around the world, flooding and climate change is reshaping urban landscapes. But some argue that design, investment and innovation could help build resilience while remodelling cities in ways that also address poverty and improve quality of life.
Urban inundation has multiple causes. Cities with rivers running through them can be affected by heavy rainfall far away. Meanwhile, global sea levels are climbing, with the Intergovernmental Panel on Climate Change predicting a change of up to 30cm by 2050. Rising sea levels put 1.4bn urban residents at risk of flooding globally, according to the UN, which estimates that by 2040 more than 2,000 cities will be less than 5 metres above sea level.
Threats to Alexandria illustrate the dangers. According to the OECD, a sea-level rise of half a metre would leave 67 per cent of the Egyptian city’s population below sea level and prompt the evacuation of 1.5mn citizens. A 1 metre rise would push this up to 76 per cent while also putting 82 per cent of city services at risk of inundation.
Residents of informal settlements are most vulnerable, since they are often closer to the risks and may lack the financial and other resources to cope with the consequences, says Vanesa Castán Broto, professor of climate urbanism at the University of Sheffield. “Informal settlements tend to be in places that are exposed to many risks, including flooding and sea level rise,” she says, because they tend to occupy cheaper land.
Climate change is part of the problem — but so is the nature of urban development. Cities need to create space and greenery that can soak up water, says Jo da Silva, global director of sustainable development at UK-based engineering group Arup. “That’s what we haven’t done. We’ve covered everything in hard surfaces.”
Wuhan, in China’s Hubei Province, is one example. Rapid urbanisation from the 1990s left the “city of a hundred lakes” with only about 30. “When you fill up the lakes, the water has nowhere to go,” says Fan Feng, China-based resilience lead for Netherlands-based consultancy Arcadis.
But while urban development has caused problems, smart planning and design can help to address them. In Wuhan, says Feng, Arcadis has been working with government agencies to create a “sponge city”, which absorbs water through nature-based infrastructure such as permeable pavements, green roofs, artificial ponds and wetlands.
Many now see such solutions as increasingly effective in building urban flood resilience, complementing or replacing “grey infrastructure” of concrete and steel. “We can fix our cities by bringing nature back into them,” says Da Silva.
The benefits of harnessing nature go beyond resilience. For example, mangroves — tropical and subtropical coastal wetlands — shield communities from storm surges, providing flood protection services estimated to be worth $855bn over their lifetimes, according to the World Bank.
In addition, however, mangroves absorb carbon emissions, support local seafood businesses and create eco-tourism destinations. “What you have with mangroves is a rich ecosystem that attracts everything,” says Castán Broto.
Whether green or grey, resilience measures can enhance urban quality of life, as was the case when Copenhagen redirected polluted stormwater from its port into sewers. “In a couple of years, the port water became so clean you could swim in it,” says Bjarke Ingels, the Danish architect and founder of the Bjarke Ingels Group (BIG). “No one had foreseen this.”
Today, Copenhagen’s Harbour Baths are recreation centres where people swim, sunbathe and picnic. “It completely recreated the way we think about the port,” says Ingels, whose company designed Islands Brygge, one of the first of the Harbour Baths.
Meanwhile, BIG’s River Ring scheme in New York City uses restoration of natural habitat to strengthen waterfront flood resilience and increase the visual appeal of housing on former industrial caissons in Williamsburg. “You end up with a soft barrier that eliminates the energy of the wave action before it gets to the beach,” says Ingels.
One challenge is that cities are complex systems where flood resilience involves government agencies and companies, as well as urban residents. This makes collaboration essential, says Daniella Levine Cava, mayor of Florida’s Miami-Dade County, where residences, offices, roads and septic and drainage systems lie within feet of sea levels.
Miami-Dade covers 34 cities, roughly half of which are incorporated self-governing cities. The county’s Adaptation Action Area resilience plan is thus a multi-jurisdictional effort. “It’s extremely complicated,” says Levine Cava.
Also critical, she adds, is working with communities: “They are consumers of government programmes, and they need to be informed so they can advocate for effective interventions.”
Castán Broto agrees. Cities, she says, must take steps to ensure they are listening to their residents and providing the support they need to participate in flood resilience efforts. “Communities have a lot of answers,” she says. “But they cannot do it alone.”
