Crop Circles in the Desert

Over the past three decades, Saudi Arabia has been drilling for a resource more precious than oil. Engineers and farmers have tapped ancient reserves of water, dating back to the last Ice Age, to grow crops in the desert. This series of false-color satellite images show the evolution of agricultural operations in the Wadi As-Sirhan Basin. New vegetation appears bright green while dry vegetation or fallow fields appear rust colored. Dry, barren surfaces (mostly desert) are pink and yellow. Saudi Arabians have reached this underground water source by drilling wells through sedimentary rock, as much as a kilometer beneath the desert sands. Rainfall averages just 100 to 200 millimeters per year and usually does not recharge the underground aquifers, making the groundwater a non-renewable source. Although no one knows how much water lies beneath the desert—estimates range from 252 to 870 cubic kilometers—hydrologists believe it will only be economical to pump it for about 50 years.

See earthobservatory.nasa.gov/IOTD/view.php?id=77900