Tehran may be forced to implement a partial evacuation of its population if rainfall does not occur by the end of December and dams remain empty, a water resource management expert has warned.

The startling admission was made by Darioush Mokhtari, a senior water resource management expert. He stated that even with the complete depletion of dams and reduced flow from some drinking water wells, part of Tehran's water needs can still be met; however, people may have to be relocated as water supplies disappear. The situation has become so acute in recent hours that Friday Prayer leader Ahmad Khatami also mentioned the need to conserve water to parishioners at Tehran University.

"This time period is exactly the critical point - a situation that cannot be passed without temporary evacuation of part of the city's population," he said, according to Khabaronline.

Tehran currently has more than 13mn resident population and approximately 2mn non-resident population who travel through it daily. The city has been the main industrial base since the 1950s, carrying a large portion of Iran's industrial burden. This heavy load on the Tehran plain led to today's critical situation.

Dams surrounding Tehran supply more than 70% of the city's water resources, whilst around 700 drinking water wells provide the remainder. More than 250 additional wells are used to supply water for green spaces.

With more than 200 days of drought, officials have begun drafting worst-case scenarios to cope with dwindling supplies. Following warnings about plummeting dam levels and the need for public restraint, Energy Minister Abbas Aliabadi recently cautioned that authorities might be forced to cut water pressure to zero on some nights, which, according to social media, is already happening in parts of the city.

Water levels across the supplying dams are now at a critical level, with one of the main man-made lakes, Latyan Dam dropping to just 9% capacity following months of drought.

The situation across the other several dams feeding the megacity has also seen historic lows, with previous reports by IntelliNews reporting averages of just 5% capacity.

Iran has recorded just 3.5 millimetres of rainfall over the past 50 days, equivalent to 18% of the normal average, with 20 provinces receiving no precipitation at all in the longest drought in recorded history.

Mokhtari said that whilst urban water crisis response appears to be the responsibility of water and wastewater companies, the main root must be sought in comprehensive and detailed plan approvals for large cities by the Supreme Council of Urban Planning and Architecture.

"The crisis began where city limits expanded, uncontrolled density sales became prevalent, and municipalities issued permits based on Article 5 Commission approvals and macro urban planning policies. The result was uncontrolled population growth and heavy loading on the capital's limited water resources," he stated.

The expert added that Tehran Water and Wastewater Company must communicate transparently and regularly to gain citizens' trust and obtain their participation in crisis management. He noted that water supply by tanker can temporarily cover some areas, whilst citizens who can leave Tehran can help crisis management by reducing the city's population burden.

Mokhtari said that the emergency action programme is designed for when dams remain completely empty until mid or late December and practically no surface water source is in Tehran's network circuit.

"In such conditions, although very difficult, there is the possibility of temporary passage through the crisis, but it is essential that municipalities stop issuing any new building permits and the water and wastewater company also refrain from issuing new connection permits for the next few decades," he stated.

He said that Tehran Province Water and Wastewater Company can temporarily control the crisis with distribution management and targeted use of underground resources.

"Precise examination must be carried out to determine whether well water resources can compensate for the low rainfall period and absence of river flows," he stated.

Given the Tehran metropolis' 950 square kilometre expanse, this work is very difficult and areas dependent on dam water will be the first areas subject to temporary evacuation.

"Tehran's water crisis is a serious warning," Mokhtari said, "a warning that if not heard today, tomorrow there will be no opportunity left to respond to it."