Not war but drought has forced more than 100,000 people in northern Iraq to abandon their homes since 2005, with 36,000 more on the verge of leaving, says UNESCO.

The four-year drought and excessive well pumping have led to the collapse of an ancient system of underground aqueducts, or karez.

Only 116 of 683 karez systems are operational, according to a study by the UN Educational, Scientific and Cultural Organisation. The study says 70 per cent of active karez have dried up.

The Paris-based organisation says the study, the first to research the effects of the droughts on the system of underground aqueducts, concludes that "swift and urgent action is needed to prevent further population displacement". UNESCO said it considers the plight of the karez system and the migration as an early warning sign for the future of water in the area.

The study provides the Iraqi government with its first inventory of karez, UNESCO said, 84 per cent of which are located in Sulaymaniyah and 13 per cent in Erbil province. A karez can produce enough drinking water for 8640 people and 1440 households, UNESCO said. The technology was developed in ancient Persia.

"Before the onset of the drought, the greatest threats to the karez in Iraq were political turmoil, abandonment and neglect," a UNESCO statement said. "Today, few people in Iraq know how to maintain or repair them, contributing to their state of disrepair."

Entire communities have fled because of the lack of water, with populations declining nearly 70 per cent, UNESCO said. It cited as an example the village of Jafaron, where 44 of its 52 karez have gone dry since 2008. The lack of water has left barren 113 hectares of irrigated land.

UNESCO said it has been working with Iraq since 2007 to rehabilitate the karez system. In 2010, it will launch the Karez Initiative for Community Revitalisation, to help Iraqis rebuild the aqueducts.