CLIMATE CHANGE

Rising Seas + Dams + Aquifer Pumping = Delta Blues

By ANDREW C. REVKINMARCH 28, 2014, 11:32 AM


Kadir van Lohuizen for The New York Times
Bangladesh, with its low elevation and severe tropical storms, is among the countries most vulnerable to the effects of climate change, though it has contributed little to the emissions that are driving it.

Gardiner Harris has a comprehensive feature in The Times today taking a close look at the impact of advancing seas and sinking landscapes on Bangladesh, with a related story taking a global lookat sea-level rise from global warming.

There’ll be much more from The Times in the next few days as Justin Gillis reports from Yokohama, Japan, on the scheduled release on Monday of the latestIntergovernmental Panel on Climate Change report on global warming impacts, adaptation and vulnerability.

What’s particularly notable and disturbing about the situation in crowded delta regions like Bangladesh is that the rise in sea levels is, for the moment at least, not even close to the main driver of inundation risk.

The damming of Asia’s great rivers has greatly reduced the sediment flows that created the deltas in the first place and maintain them now. James Syvitski and co-authors provided a valuable overview of this problem in “Sinking deltas due to human activities,” an important Nature Geoscience paper in 2010.

That paper and other studies also point to the importance of groundwater pumping (and in some places gas drilling and extraction) in driving alarmingly fast subsidence of urban areas, including in Dhaka, where, as Harris reports in The Times, many of those leaving coastal areas are bound.

A recent study cited in the Bangladesh newspaper the Daily Star concluded that Dhaka is sinking 12.91 millimeters a year. That is 10 times the rate at whichsea level in that part of the Bay of Bengal is rising.

And Dhaka is not an isolated case, nor is that city close to the worst case. For that, peruse this dismaying 2013 paper in Remote Sensing of Environment: “Sinking cities in Indonesia: ALOS PALSAR detects rapid subsidence due to groundwater and gas extraction.”

Here’s an excerpt:
The data reveal significant subsidence in nine areas, including six major cities, at rates up to 22 cm/year. [Yes, that's nearly 9 inches a year. Compare that to a recent estimate for sea level rise near Jakarta of5.7 millimeters a year - 0.22 inches a year.] Land subsidence is detected near Lhokseumawe, in Medan, Jakarta, Bandung, Blanakan, Pekalongan, Bungbulang, Semarang, and in the Sidoarjo regency. The fastest subsidence occurs in highly populated coastal areas particularly vulnerable to flooding. We correlate the observed subsidence with surface geology and land use.

Despite the fact that subsidence is taking place in compressible deposits there is no clear correlation between subsidence and surface geology. In urban areas we find a correlation between rapid, patchy subsidence and industrial land use and elsewhere with agricultural land use.

This suggests that the subsidence is primarily caused by ground water extraction for industrial and agricultural use, respectively. We also observe subsidence associated with exploitation of gas fields near Lhokseumawe and in the Sidoarjo regency. A continuation of these high rates of subsidence is likely to put much of the densely populated coastal areas below relative sea level within a few decades.

The bottom line, of course, is that coastal communities in many developing countries, from flood-prone agricultural delta lands to crowding cities, face a very soggy future.

Part of that future — particularly over the long haul — is being shaped by global warming.

But it would be a distracting mistake to shape the debate around rising inundation risk in such regions as a finger-pointing exercise related to greenhouse gases.

A better approach would be to foster collaborative projects aimed at resilient urban design, improved water treatment and efficiency (to cut demand for groundwater pumping) and landscape management in fast-growing delta cities and nearby regions.

The World Bank has the right idea in several initiatives it is pursuing in South Asia. The Rockefeller Foundation’s 100 Resilient Cities project is also pointed in the right direction.

A Dutch-Bangladeshi project that I wrote about in 2008 is a nice template: “Can Crumbling Himalayas Protect Bangladesh From Rising Seas?”

I’ll check to see how that’s going and report back.

http://dotearth.blogs.nytimes.com/20...g-delta-blues/