http://pdf.usaid.gov/pdf_docs/PNADH905.pdf Geology, Water, and Wind in the Lower Helmand Basin, Southern Afghanistan], Scientific Investigations Report 2006–5182; John W. Whitney; U.S. Department of the Interior & U.S. Geological Survey; published 2006 The area of agricultural land under irrigation more than halved between 1979 and 2002 to around 1500000 hectares , although this has since been increased. [