Reuters

Groundwater pumping and rising sea levels could leave millions flooded out of their homes.

When flood water inundated much of Jakarta, Indonesia, in 2007, many were quick to blame climate change. The city is certainly susceptible to rising oceans, with about 40 percent of land below sea level. But it's also not doing itself any favors. The city has been carelessly pumping its groundwater, leading neighborhoods to sink further.

"Jakarta is one of the worst sinking cities in the world," says JanJaap Brinkman, a hydrologist with the Dutch water research institute Deltares, which has been working in the city to help plan for what may be a very wet future. He was at the recent American Planning Association national conference to explain some of the city's major issues.

Venice and Ho Chih Minh City face similar problems. But unlike Venice, which is subsiding at a rate of about 2 millimeters per year, or Ho Chih Minh City, which is sinking about 2 centimeters per year, parts of Jakarta are sinking at 10, 15 or even 20 centimeters per year, according to Brinkman.

Population growth is a big part of the problem. Brinkman says that the current metropolitan population of about 30 million is expected to grow to more than 40 million in the next 20 years. Feeding this growth has been the relatively unchecked pumping of deep groundwater. This water, hundreds of meters below the city, is a not easily refilled and those dry cavities greatly exacerbate the city's subsidence. And it doesn't seem to be stopping.

"If deep groundwater extraction is not stopped, Jakarta will sink at least another five to six meters by the end of the century," Brinkman says.

He says the problem has been underway for decades. The first available baseline data is from 1974. Between 1974 and 2010, the vast majority of the city has subsided. Large swaths have sunk between 25 and 70 centimeters during that time, but the more heavily populated areas near the shore have sunk 1.4 meters, 2.1 meters and in one especially sensitive area in the city's core 4.1 meters.

A 30-kilometer seawall meant to prevent the ocean from flooding has been built, but that, too, is sinking. Brinkman says the city is facing potentially catastrophic flooding should that seawall break. Within 48 hours of a breach, a low-lying section of the city home to nearly 1 million people would be completely flooded. And all that seawater could flow into the city's fresh water supplies, magnifying the already intense drinking water issues.

But Jakarta and the Indonesian government are trying to find some solutions. One option is to build an even larger sea wall and to possibly spread development onto landfills in Jakarta Bay. The sea wall is currently in the planning stages, and is expected to be built by 2025.

Brinkman notes, however, that Jakarta can't just build its way around this problem. He argues that the city needs to take more control over the groundwater pumping there, limiting it or, ideally, stopping it altogether. Unless there are major changes in the way the city addresses its water needs, the flooding seen in 2007 will become much more common and vastly more devastating.

Photo credit: Reuters/Supri Supri

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