The Global Urbanist

News and analysis of cities around the world

"We can buy ourselves 300 years" say planners on fighting rising sea levels in delta cities

As coastal and delta cities face the impacts of rising sea levels due to climate change, planners are readying with a combination of sea wall solutions, ecological engineering and urban design, which one says will buy us three centuries of security.

Anthony Flint/Citiscope

Anthony Flint/Citiscope

Cities: Shanghai, Hong Kong, Dhaka, Jakarta, New Orleans, New York-Newark, San Francisco-Oakland

Topics: Climate change, Flooding and storms

Oil spills like that in the Gulf of Mexico are not the only peril facing tidal cities this century. We face a global rise in temperatures that will trigger rising sea levels, more intense storms, and an array of other chain-reaction disruptions to our current way of life.

And in typically sinister fashion, these impacts will hit hardest in the places most people live. Rapid urbanisation has intensified in coastal areas in all regions of the world, and in coastal and delta mega-cities this includes widespread informal settlements, a recipe for disaster for the most vulnerable populations.

Cities in general can play a role in mitigation — the reduction of greenhouse gas emissions — to help lessen the rise in temperatures. But coastal cities must also adapt to the impacts listed above, in parallel to mitigation measures, and in many ways integrated with them. There is no more urgent role for planners in the years ahead than to plan and help implement adaptation to climate change, says Edward Blakely, the former recovery director for New Orleans.

Coastal cities are already well aware — some painfully aware — of the breadth of the problem. Jakarta is confronting annual flooding that strains its colonial-era layout, and Dhaka has struggled with stronger typhoons.

At the Yangtze and Pearl river deltas in the Shanghai and Hong Kong regions, chronic flooding, coastline erosion and wetlands deterioration, storm surges, and punishing storms are wreaking havoc on the very areas that have attracted the most intense in-migration and urbanisation. Sewer overflow and saltwater intrusion, impacting on drinking water, public health and agriculture, are key areas of concern, as are the vulnerable infrastructure such as power plants, port and refining facilities that will be flooded and potentially permanently underwater in the decades ahead.

Planning for rising sea levels

The city ravaged by Hurricane Katrina five years ago has had the most vivid glimpse of the future. New Orleans' path ahead ranges from evacuation planning and relocation, 'hard' solutions such as seawalls, weirs, tidal barrages, levees and the redirection of waterways, to the restoration of natural systems to manage flooding. "The world is watching not only the city, but the planning field as well," said EPA Administrator Lisa Jackson, who grew up in New Orleans, speaking at the American Planning Association's (APA) National Conference in April.

The adaptation strategies detailed at the conference reflected a comprehensive approach informed by the people who know water better than anyone — the Dutch. The most promising innovations are based on the concept of giving water more space — "room for the river" — in terms of spatial planning.

The approach involves lowering dikes in targeted areas to better enable flood protection in other areas with high populations or valuable infrastructure, says Tulane University's Douglas Meffert. While this practice sounds counterintuitive, allowing certain natural habitat or in some cases, farmland areas to flood during high river stages reduces the vulnerability of nearby urban centres, he says.

A critical component is the role that nature is allowed to play. The restoration of wetlands and natural systems in coastal and delta cities has moved to the forefront. A promising model is found in the Yangtze River estuary's wetlands and mudflats, which continue to grow due to the dynamics of riverways, tides, and sediment.

When Shanghai's Pudong wetland was drained and developed in the 1990s to construct the Pudong International Airport, the Jiuduansha Shoals in the Yangtze Estuary were ecologically engineered to mitigate for this wetland loss and create a new habitat for the migratory shorebirds and waterfowl. The attraction of the new vegetated habitat had the added advantage of reducing bird strikes in jet engines, but the big benefit is typhoon hazard reduction for nearby developments and infrastructure.

Other efforts in China were detailed by Lingqian Hu, senior regional planner at Southern California Association of Governments, who presented a Tsinghua University paper, "Climate change and urbanisation in the Yangtze River delta"; and He Canfei, professor at Peking University and associate director of the Lincoln Institute-Peking University Centre for Urban Development and Land Policy in Beijing.

Future projects could not only use natural systems as flood control solutions but better use diversions for wetland restoration and creation projects, as well as improved water storage practices in population centres, such as catch basins, green roofs, gardens, recreation parks, waters squares and pervious surfaces.

"We're capable of doing these things," said Robert Yaro, president of the Regional Plan Association. He reminded the audience that a century ago, Charles Eliot used a combination of hard infrastructure and natural systems to manage the Charles River in Boston, which was followed by the Charles River Dam project to further guide storm surges and flooding.

In the long haul, Yaro said, coastal cities will see dramatic changes — huge tidal barriers at the Golden Gate and ringing New York City, with the San Francisco Bay and Long Island Sound potentially turned into freshwater lakes. Large areas will be uninhabitable and water supplies will be a particular problem, he said. "We can basically buy ourselves 300 years," Yaro said. "We're at the place where Amsterdam was in 1890."

Taking adaptation seriously is a first step; paying for it will be the next. Blakely suggests that in the U.S. cities might pay into a national adaptation fund, on an insurance model. Those metropolitan regions that take the best protective measures get a break on their premiums.

Building on these innovations will require smart people who not only understand policy, urban planning and earth science, but the dynamics of deltas, sediment, and discharge. The challenge is so daunting that it's hard to maintain hope, or to believe in much beyond the bright prospects of the seawall-building business. But adapting to climate change in coastal cities is shaping up to be the central project of planning for this century.

Anthony Flint is a Boston-based writer at the Lincoln Institute of Land Policy

Source: Citiscope

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