The U.N. refugee agency, UNHCR, and other humanitarian agencies -- including Catholic groups -- in Iraq are scurrying to ready preparations, as it is believed that the U.S.-led assault could be pushed forward as early as September. But aid groups fear they may be overwhelmed by the sheer numbers involved.
The U.N. says that as the Mosul crisis evolves, up to 13 million people throughout Iraq may need humanitarian aid by the year's end -- far larger than the Syrian crisis. This would make the humanitarian operation in Mosul likely the single largest, most complex in the world in 2016.
Bruno Geddo, UNHCR chief for Iraq, told Catholic News Service the United Nations has issued an appeal for the $284 million needed in part for the "preparation of camps ahead of the humanitarian emergency from Mosul." Geddo said a cluster of camps needs to be built in six locations in disputed territory.
"Not only do you have to make sure that the location is not in the direct range in the line of fire," he said, "but the terrain must be fit to build a camp."
He said safety and security screenings are top priorities as Sunni Muslims flood out of Mosul, controlled by the Islamic State group for the past two years. Iraqi authorities will be charged with conducting the security screenings to identify Islamic State collaborators.
Others who pass the screening may escape to the Ninevah Plains -- the ancestral heartland of Iraqi Christians for centuries -- and this will not be acceptable to either Christians or Yezidis persecuted by Islamic State militants.
"We are very sensitive to this issue. Yezidis always consistently said 'We will never again be able to live side by side with Sunni neighbors after what they perpetrated against us,'" Geddo told CNS. Yezidis and other religious minorities will be located in camps separate from Mosul's Sunni Muslims.
"Those security-cleared will be able to go elsewhere in the country based on sponsorships by family members, relatives, or religious institutions. They can fan out all the way down to Basra," Geddo said.
"This key for us to meet this massive humanitarian need," he added, "so they will not have to stay in camps but move on, on a sponsorship basis while they have been security cleared."
Hani El-Mahdi, country representative of Catholic Relief Services in Iraq, said the Catholic agency is building capacity with its personnel, Caritas, and church volunteers to administer emergency assistance to the newly displaced who choose to shelter in communities, rather than camps, in the Ninevah Plains, Zumar, Kirkuk and Dahuk.
"We are anticipating that the vast majority of the displaced, perhaps more than 90 percent, will shelter in noncamp areas," El-Mahdi told CNS. "CRS responded to the latest crisis in Fallujah in noncamp areas, and the lessons learned will be applied in this situation."
El-Mahdi said CRS does not promote using tents for the displaced people and has devised a new transitional shelter model made from locally available materials that is preferable in temperature extremes and more cost-effective than tents.
Retaking Mosul from the Islamic State group is significant because it is where the militant group's leader, Abu Bakr al-Baghdadi, announced the self-declared caliphate.
The city, once Iraq's second-largest, has also been the largest city under the extremists' control with an estimated population of 500,000 to 1 million. It is believed that Islamic State fighters there may number 10,000, but there are also reports of militants fleeing to Syria ahead of the offensive.
Reports have also emerged of families trying to escape Mosul and surrounding villages, once mainly populated by Iraqi Christians, ahead of the military onslaught. Some humanitarians fear a repeat of the recent burning by Islamic State militants of a 2-year-old girl and her family escaping their clutches.
Aid workers like Betsy Baldwin, who directs Tearfund's Iraq response, say their greatest concern is having enough water, shelter and other basic necessities available.
"The volume of people coming toward us is at such a large scale. While we will do our best, I have a feeling that it will be overwhelming to all players involved," said Baldwin. She said if people continue to trickle out of Mosul at a slower rate, the assistance will be more manageable, but humanitarians will need to be prepared for "a sudden and uncontrollable flow of people."
"We expect people to live in everything from abandoned buildings that have been disused for some time now. There are also a lot of unfinished buildings throughout the Kurdish region of Iraq," Baldwin told CNS. "People may shelter in open areas outside of villages, where they will be able to connect to existing services in villages, perhaps such as fetching water from them."
But Baldwin also warned that winterization supplies must also be planned for now, should the conflict drag on or the displacement be very widespread.
"If people are not able to return to their homes and face a protracted displacement, we need to think now about heaters, stoves and similar items," she added.