As Ali Kawu eases his handcart to a halt on a recent morning in north-east Nigeria, it is the first time he has dared to stop walking in more than 24 hours.

A day earlier, at 8am, Boko Haram militants raided his village. Kawu, 25, escaped with what he could – his wife, their three children, and kindling for a fire. They left behind their papers, six sacks of beans, up to 15 dead neighbours, and 10 kidnapped villagers. Then they walked all day and all night.

Facebook Twitter Pinterest Ali Kawu, 25, fled to the town on Monguno after being attacked by Boko Haram. The number of displaced people in this small town is comparable to the number who left north Africa for Europe so far this year. Photograph: Patrick Kingsley/The Guardian

“Every minute I would look back to see if they were following us,” Kawu says, shortly after reaching the safety of Monguno, a town recaptured from Boko Haram last year. “Walking forward, looking back, walking forward, looking back. I thought it was the end of my life.”

But safety doesn’t mean comfort. Kawu is just the latest of approximately 140,000 displaced people sheltering in this remote town of 60,000 people. North-east Nigeria has been hit by a displacement crisis that dwarfs any migration flows seen in Europe in recent years.

Since the Boko Haram insurgency began, more people have migrated to Monguno alone than left all of north Africa for Europe in the first nine months of this year.

One upshot is a food crisis that the UN warns might see hundreds of thousands die from famine next year.

About 40% more people have been displaced throughout Borno state (1.4 million) than reached Europe by boat in 2015 (1 million). Across the region, the war against Boko Haram has forced more people from their homes – 2.6 million – than there are Syrians in Turkey, the country that hosts more refugees than any other.

The comparisons mirror a wider trend across Africa. Of the world’s 17 million displaced Africans, 93.7% remain inside the continent, and just 3.3% have reached Europe, according to UN data supplied privately to the Guardian.

“No matter how many problems Europeans have, it’s nothing like this,” summarises Modu Amsami, the informal leader of Monguno’s nine camps for internally displaced people (IDP), as he strolls past Kawu’s newly erected hut. “Please, I’m appealing to Europeans to forget their minor problems. Let them come here and face our major problems.”

For 18 months, Monguno endured its migration crisis largely alone. Amsami is an IDP but decided to run Monguno’s nine camps himself in the absence of any government officials. It was not until this June, a year and a half after the Nigerian army retook the town from Boko Haram, that aid groups and civil servants felt safe to return.

“We were shaken by what we saw,” says Mathieu Kinde, an aid worker with Alima, a medical NGO that was the first to arrive. Many people were starving, having been cut off from their farmland. There was a polio outbreak – Nigeria’s first case in two years. Just one government doctor was left in the town.

To this day, the townspeople cannot farm their fields – Boko Haram remains too close to the town’s perimeter. Aid convoys from Maiduguri, the state capital, risk ambush. Most food can arrive only by helicopter, which is how the Guardian reached the town. The number of people in a famine-like state has been slightly reduced, but every week Alima treats up to 200 new cases of malnutrition. “The situation remains alarming,” says Kinde.

About 68 miles (110km) to the south, Maiduguri seems calmer. It remains under curfew but the roads into the city are largely secure, the streets are clean and its nightlife is reportedly experiencing a tentative revival. But if you know where to look, it is a city under extreme pressure.

More than 600,000 IDPs have migrated to this city of just 1.1 million during peacetime over the past three years, according to the International Organisation for Migration (IOM). About a quarter have been put up in half-built schools, or in housing projects intended for teachers and civil servants. The rest have been taken in by friends and relatives.

Facebook Twitter Pinterest The government in Maiduguri has installed 13,000 IDPs in a housing estate originally meant for civil servants. Photograph: Patrick Kingsley/The Guardian

“It’s an amazing story,” says Toby Lanzer, the UN’s assistant secretary general for the Sahel and the Lake Chad region. According to Lanzer, the local community has in effect said: “We built that as a school, but you [IDPs can] have it. And we built that as a new neighbourhood, but we will put you lot in it. How’s that for generosity, Europe?”

But that generosity has come at a price, says the governor of Borno state, the province where the majority of the fighting and displacement has taken place. Unemployment in Maiduguri has exceeded 50% since the start of the crisis, says the governor, Kashim Shettima, while more beggars gather at the major road junctions because the IDPs have few means of alternative income.

“Health facilities are at breaking point,” he says. “All resources have become overstretched. We ask all people of conscience to help.”

Across the region, about 65,000 people are suffering from famine-like conditions. Inside a makeshift clinic run by Médecins Sans Frontières in a Maiduguri suburb, you can find some of the most dire cases. On bed after bed, about 100 skeletal babies and toddlers stare vacantly into space. Many have plastic nodules stuck to their skull, to allow the nurses to attach them to a drip. Many children are so thin their scalp is the only place a visible vein can be found.

“Getting food became so difficult after my husband was killed [by Boko Haram],” says one mother, whose malnourished three-year-old lies motionless on the bed beside her. “I would beg every day but I wouldn’t get more than 100 naira [25p] a day. And that’s how he got hungry.”

Facebook Twitter Pinterest A mother feeds her malnourished child at a nutrition clinic run by Médicins Sans Frontières in Maiduguri. Thousands of children have died of starvation and disease in Boko Haram-ravaged north-eastern Nigeria. Photograph: Sunday Alamba/AP

The international community has largely failed to help: UN funding is still 61% ($297m) short of its target. Local residents have stepped in where they can. Babakara al-Kali, a Maiduguri businessman, has given a plot of land to about 3,000 IDPs – forgoing the 10m naira (£25,000) he previously charged construction workers and mechanics to rent it every year. “If you help someone, God will help you,” Kali says. “So I decided to help them.”

Still, the conditions inside this makeshift camp are abject. Streams of slurry trickle through the site. A family mourns a child who died yesterday of hunger. Two elderly men have become blind in recent days and the camp’s elders blame the lack of food. Some residents spend their mornings collecting spilt grain at the local market; in the afternoons, they sift through them piece by piece, sorting the edible grains from the rotten ones.

“We have lost count of the number of people killed by hunger,” says Bulama Modusalim, the camp’s informal leader.

Aside from their physical problems, many of the IDPs across the region are suffering from psychological trauma. Almost every interviewee tells a story of being woken at dawn by gunfire, of emerging from their huts to find Boko Haram fighters killing their neighbours or kidnapping their relatives.

Facebook Twitter Pinterest Ali Falfami, 73, had his hand removed after being shot by Boko Haram fighters. Photograph: Patrick Kingsley/The Guardian

Ali Falfami, 73, has a missing hand; it was amputated after being shot by Boko Haram. Karu Modu, 28, has a missing son – he was shot by the militants – and a missing husband: they slit his throat. Modu survived because she agreed to watch their murder. “They forced me to watch them die so that I would not be slaughtered,” she says, before breaking down in tears.

Modu was then kidnapped and held for nearly two years. After escaping with a group of fellow captives, six of their children died of thirst as they trekked to the safety of Maiduguri. On arrival, they were initially ostracised. People feared the women had become indoctrinated during their time with the extremists, and were wary of talking to or even sitting with the returnees.

Facebook Twitter Pinterest Karu Modu, 28, was kidnapped and held by Boko Haram for two years. Photograph: Patrick Kingsley/The Guardian

These are not isolated experiences. The #BringBackOurGirls campaign has focused on the group of schoolgirls kidnapped from Chibok in 2014 – but away from the media spotlight, thousands of others are believed to have also been abducted in other incidents. At one point, Boko Haram controlled an area the size of Belgium and killed an estimated 20,000 people. Now the group is in retreat, but millions more still face food shortages.

“The narrative of this deepening humanitarian crisis in north-east Nigeria has been largely overlooked by the media, whose focus remains on the kidnapping of roughly 300 Chibok school girls,” says Orla Fagan, a spokesperson for UN’s office for coordination of humanitarian affairs.

“Each one of the girls who remains captivity is a minuscule representation of the millions of Nigerians who now face starvation across the north-east as a result of Boko Haram violence. They are some of the poorest, most vulnerable members of society, who also continue to struggle for their basic needs to survive each and every day.”

Many of them are being encouraged to return home where they face uncertain futures. The Nigerian army has retaken several key towns from the insurgents, and the government wants their former residents to go back to what they say are now safe areas. But the reality is more complex: the roads in and out are often still contested, as are the fields surrounding the towns. Many buildings lie in ruins and, as a result, returnees are often forced to live in IDP camps even after they have nominally reached their hometown.

Facebook Twitter Pinterest Bulama Modusalim is the informal leader of a makeshift camp for IDPs displaced by the Boko Haram insurgency in north-east Nigeria. Photograph: Patrick Kingsley/The Guardian

Bulama Modusalim, the leader of the informal camp in Maiduguri, took a group of villagers back to Konduga in August, after the government assured them it was safe. “But when we went back we found that Boko Haram was still [in the surrounding area],” says Modusalim. “We went back and we found our houses were destroyed. We couldn’t go further than 1km from the town, so we couldn’t farm.”

Eventually, the situation became so desperate that they went back to Maiduguri, despite the poverty they knew they would face there. In a choice between war and starvation, they would rather risk the latter.

Amid all this misery, Boko Haram is the most obvious explanation for what has gone wrong. Nearly everyone is running from the jihadis who still control significant parts of the Lake Chad basin. But what led to the group’s rise in the first place? Local leaders say the group was initially able to present its fighters as victims of police brutality – and more generally positioned Boko Haram as a radical alternative to the high levels of regional poverty and unemployment.

But according to several interviewees, including the local governor, this social alienation was partly fuelled by rapid climate change. North-east Nigeria borders Lake Chad, a vast inland lake that supplies water to about 70 million people in four countries – Nigeria, Chad, Cameroon and Niger. But since the 1970s, it has shrunk by 90% – from 25,000km2 to less than 2,500km2. And those who live near its former shores say this shrinkage is one indirect cause of violence in the region, and the subsequent displacement.

Modu Amsami, the IDP who runs the nine camps in Monguno, comes from the village of Gumnari, which was once just 2km from the lake. Now it’s 18km away.

“In the 70s, you could put this tree in the lake,” Amsami says, pointing at a nearby tree, “and you wouldn’t even see it. Now if I walked in there, the water wouldn’t even reach my chest.”

As a child, Amsami’s father would tie him to a tree to stop him entering the lake and being eaten by crocodiles. Today there would be no need. The water is nowhere in sight and it’s difficult to even see a crocodile.

Facebook Twitter Pinterest Modu Amsami stands next to a tree that he says would once have been submerged by Lake Chad. Now the waters would not reach his shoulders, he says. Photograph: Patrick Kingsley/The Guardian

All this has led to unemployment for thousands of fishermen and farmers – including several people from Amsami’s family. He reckons this worsened living conditions, created a wave of unemployed and disaffected youth – and so helped fuel the anger and resentment that created Boko Haram. “If the Lake Chad water was normal,” says Amsami, “all these problems [with Boko Haram] would be eliminated economically, because nobody would have time to do all these things.”

According to the IOM, few of the roughly 35,000 Nigerians who have in Europe this year are fleeing from the insurgency in the north-east. But the west would be wise to take the Lake Chad crisis seriously, lest the millions seeking sanctuary in the region decide to move towards Europe. Lanzer says he is “willing to bet a month’s salary that the proportion of people who will arrive in Europe from Nigeria, Chad, Cameroon and via Niger will grow substantially”.

Shettima speaks in even starker terms: “As long as the underlying problems that precipitate the crisis are not met, then there is a risk that more Nigerians will try to go to Europe.

“At the moment, most of them are economic migrants, but if this madness is not solved, believe me you will see a mass of humanity trying to get to Europe via the Mediterranean.”