for National Geographic News
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.
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