Megacities contend with sinking land


Subsiding land is a bigger immediate problem for the world's coastal cities than sea level rise, say scientists.

In some parts of the globe, the ground is going down 10 times faster than the water is rising, with the causes very often being driven by human activity.

Decades of ground water extraction saw Tokyo descend two metres before the practice was stopped.

Speaking at the European Geosciences Union General Assembly, researchers said other cities must follow suit.

Gilles Erkens from the Deltares Research Institute, in Utrecht, in the Netherlands, said parts of Jakarta, Ho Chi Minh City, Bangkok and numerous other coastal urban settlements would sink below sea level unless action was taken.

His group's assessment of those cities found them to be in various stages of dealing with their problems, but also identified best practice that could be shared.

"Land subsidence and sea level rise are both happening, and they are both contributing to the same problem – larger and longer floods, and bigger inundation depth of floods," Dr Erkens told BBC News.

"The most rigorous solution and the best one is to stop pumping groundwater for drinking water, but then of course you need a new source of drinking water for these cities. But Tokyo did that and subsidence more or less stopped, and in Venice, too, they have done that."

The famous City of Water in north-east Italy experienced major subsidence in the last century due to the constant extraction of water from below ground.

Written By: Jonathan Amos
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  1. Surely something as easily demonstrated as “land sinking” will be accepted and corrected by politicians and leaders around the globe. I mean, look at how well they have responded to and corrected our Carbon Dioxide emission crisis.

  2. New Orleans is 15 feet below sea-level and sinking, with extraction wells helping it on its way down. They were warned by the National Geographic and others how deep the flood would be when the next hurricane hit, – a year before Katrina hit them, so they would have plenty of OPPORTUNITY TO BE PREPARED –

    Oh dear!!! Planning for climate events was, and is, not a US strong-point!

    Coastal cities sinking with oil and water extraction causing subsidence, along with rising seas and bigger storms from global warming. – The damage could prove to be VERY expensive.

    Perhaps Hurricane Sandy was a wake-up call!

    A Slow Process

    Of course, big announcements and sweeping recommendations have come after other big disasters. Think of the lofty Gulf Coast plans after Katrina, which aside from the reinforcement of levees, have largely been left to languish. How much the Sandy recovery winds up changing disaster preparedness and infrastructure is yet to be seen.

    Some argue that the federal government has already been too slow to turn recommendations into action.

    “It’s been a slow process,” said Holland of ICLEI-Local Governments for Sustainability, “partially because federal agencies have been hamstrung by Congress. From the sequester to the shutdown, the federal agencies haven’t been empowered to implement these things as quickly as they’ve needed to.”

    Or perhaps some dream on in carbonaceous delusion!

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