Tehran Times - Iran�s National Cartographic Center (NCC) has warned that northcentral Alborz province, adjacent to Tehran, is suffering from land subsidence by an annual rate of 29 centimeters, which must be tackled before incurring great loss, IRNA reported on Tuesday.

Land subsidence, a gradual settling or sudden sinking of the Earth's surface due to subsurface movement of earth materials is mainly caused by aquifer-system compaction, drainage and decomposition of organic soils, underground mining, oil and gas extraction, hydro compaction, natural compaction, sinkholes, and thawing permafrost.

Masoud Shafiei, the NCC director, in a letter to responsible officials has warned about the phenomenon and requested them to take urgent measures.

According to a study carried out by the NCC, the area most affected by subsidence is Alborz province, as an area of 700 square kilometers is running down with the highest annual rate of 29 centimeter.

Mehrshahr country is also subsiding at a rate of 18 centimeters annually, in addition to other counties running down by 5 to 8 centimeters.

Earlier in June, Ali Beitollahi, secretary of the national working group on natural disasters said that 18 densely populated provinces are vastly subsiding and consequently become increasingly vulnerable to flooding and natural incidents as well as bearing huge infrastructure damage.

Excessive groundwater withdrawal, Inefficient irrigation methods in addition to digging illegal wells are the main causes of groundwater extraction-induced subsidence, as out of 50,000 wells pumping underground water resources in the capital, 30,000 are illegal not having a permit, therefore, the country�s ground water condition is worrisome, he added.

In September 2018, geologist Mohammad Javad Bolourchi said that in the Iranian calendar year 1384 (March 2005-March 2006), the subsidence rate in Tehran plain has been measured at 17 centimeters a year, it has been measured 12 centimeters in Varamin county, in southern Tehran.