Iran Sinking as Groundwater Resources Disappear
By Kate Ravilious
for National Geographic News
|September 22, 2008|
Iran's insatiable demand for water, which is being drawn out of aquifers far faster than it can be replenished, is causing large chunks of farmland to sink and buildings to crack, according to a new study.
Estimates suggest the water levels in Iranian aquifers have declined by an average of nearly 1.5 feet (half a meter) every year over the last 15 years.
As the water is removed, soil and rock lose their support, leading to compaction and sinking.
Satellite radar observations—collected by Mahdi Motagh from GFZ, the German Research Centre for Geosciences based in Potsdam, Germany, and his colleagues—are showing just how serious the problem is.
Combining satellite radar images of the land surface dating back to 1997 with water level data, the team has shown that water withdrawal from aquifers is creating a major dilemma.
Demand Greater Than Supply
Much of Iran is very dry, and only 10 percent of the country receives enough rainfall to meet its needs. The remainder of the country is heavily reliant on groundwater, with around 50 percent of Iran's water being supplied by aquifers.
Population growth, combined with economic development and a boom in industry and farming, has caused a huge increase in demand for water in Iran, according to Motagh.
But the slow-filling aquifers have not been able to keep up.
"Most of the aquifers have recharge times of thousands of years," he said.
Between 1971 and 2001 the water table in the region sunk by 50 feet (15 meters), and satellite radar observations reveal land subsidence rates of up to 20 inches (50 centimeters) a year in some places.
"We see sinkholes and cracks that can be one or two meters wide and several meters deep," said Motagh, whose findings are published in the journal Geophysical Research Letters.
Currently the worst affected areas have been agricultural regions, such as the pistachio growing area on the Rafsanjan Plain in central Iran.
Digging Deeper for Water
Farmers consistently have to dig deeper wells every year, said Kourosh Mohammadi, from Tarbiat Modarres University in Tehran, Iran, who wasn't involved in the study.
Iran's cities are showing the strain too.
"In urban areas such as Tehran, residential blocks have also been affected by subsidence," Motagh said. Cracks are appearing in buildings, roads, and pipelines, added Mohammadi.
To make matters worse, the loose, dry soil is making earthquakes more dangerous, because the ground shakes more easily, according to Motagh.
An Old Problem
Iran isn't alone in facing these problems.
"This is quite consistent with similar basin subsidence that occurred in the western United States [near San Jose in the San Francisco Bay Area, in the Great Valley, and other basins in California] in the 20th century," said Roland Burgmann, from the University of California, Berkeley, who wasn't involved with the study.
Nowadays cities such as San Francisco import their water from the Sierra Nevada mountains. Similar mitigation schemes, along with better management of water supplies, may help ease the problem in Iran. But Burgmann thinks it is going to be tough.
"This can only be mitigated by finding water elsewhere or by drastically reducing water use for agriculture, industry, and personal use, neither of which will be easy in Iran or many other countries facing similar water crises," he said.
Climate change may exacerbate the problem, according to Motagh. Climate models predict a reduction in rainfall and an expansion of existing arid and semi-arid regions, such as Iran.
Motagh speculates that water removal and subsequent subsidence is likely to become an issue in many Middle Eastern countries.
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