Her home in the far east of Upper Nile state has been a relatively peaceful rebel stronghold since ethnic Nuer people rejected President Salva Kiir’s government in December. But the men in Maiwut County have joined the war, Chuol says, leaving their families to fend for themselves.

“There was no food and water in the village. Most of the women with children, they came to the camp,” she says, sitting amid a large huddle at Kule refugee camp in Gambella, Ethiopia, with women and children from six families. “It’s better here. I don’t like where I came from.”

Chuol, 30, is part of an exodus that has led more than 90,000 South Sudanese to Gambella over the past four months – 95% of them women and children, and 70% of them children, according to the International Organisation for Migration.

The civil conflict in South Sudan started after rivalry between Kiir and his former deputy Riek Machar, a Nuer, spilled over into fighting between soldiers. An uprising by the Nuer followed in the states of Upper Nile, Jonglei and Unity. The Nuer accused Kiir’s security forces from the Dinka group of ethnically targeted killing. Thousands of people have died and more than a million have been displaced in the clashes. Aid agencies are warning of an impending humanitarian crisis.

At Kule, 50km (31 miles) from Pagak, where arrivals have to register, Ethiopia’s government and partners administer, treat, feed and organise shelter for more than 33,000 refugees.

On one side of a main access road, oil, salt, sugar, rice and peas from the World Food Programme (WFP) are stacked in a white tent. Mothers emerge from another tent with medical cards from a feeding programme run by Goal, the Irish humanitarian charity.

Opposite are patches of bare earth, vacated by refugees who moved a few hundred metres to higher ground after rain created puddles and mud, says Abdulkerim Delile, clinical team leader at Kule for the Administration for Refugee and Returnee Affairs. Gambella’s regional government chose the “temporary” locations while permanent sites were cleared and shelters built. Kule’s population has almost reached its capacity of 40,000, so a new site a few kilometres away has been identified to accommodate refugees, who are arriving at a rate of more than 1,000 a day according to Delile.

The United Nations Refugee Agency (UNHCR) and the government initially didn’t realise the new camps would flood, says UNHCR’s Ethiopia representative Moses Okello. Refugees have also started moving to more elevated land at Leitchor and extra sites above floodplains are being made available near both camps, he says. “We will be able to deal with this situation. The idea here is to be ahead of any influx that would come,” he says. “I don’t see us getting stuck with people in water-clogged locations.”

The onset of the rainy season, which lasts from June until October, will also create a critical problem within South Sudan, as it makes half the country inaccessible by road, says Valerie Guarnieri, WFP’s regional director for east and central Africa.

Due to “security concerns”, the government in Juba only recently granted permission for WFP to transport food into South Sudan from Ethiopia by plane and truck. “Insecurity, border restrictions and other barriers to humanitarian access are causing serious problems for WFP moving food and staff into and around South Sudan,” says Guarnieri.

Aid agencies have so far received $479m (£285m) for South Sudan, significantly less than the $1.27bn the UN said was needed in February. Emergencies in places such as Syria and the Central African Republic are already testing donors’ stretched budgets.

“There is a growing gap between the humanitarian needs created by a series of protracted crises and the resources available,” says Guarnieri, adding that donors recently took an “important step” by making fresh pledges and commitments.

Many children arrive at Kule severely malnourished after their families have walked for weeks to escape areas such as Malakal, the devastated capital of Upper Nile. Machar’s rebel fighters are understood to be planning a fresh assault on the city, as well as on key strategic locations in the Upper Nile’s oil fields. Despite their current hardship, Chuol and her friends, like many other Nuer women, say they support the “freedom fighters”.

The volatile situation makes it impossible to predict inflows with confidence, says Jordan Davidoff, an emergency coordinator for Médecins Sans Frontières (MSF). “It’s about the unpredictability of populations and conflict and the way people respond en masse to different things like rain,” he says,adding that the situation is “as bad as any” crisis and “it’s not clear when it will stabilise”.

There are also many logistical complications. Gambella is already home to a number of Nuer people, many of whom have come east over the past 60 years looking for pasture for their cattle, or as refugees. Infiltration of the camps by Ethiopian Nuer seeking food and cooking utensils is a serious problem, says one visiting charity boss.

Another issue is the lack of intensive medical care at Kule. MSF runs an emergency clinic, but it’s 9km from the camp, at the town of Itang, and children have died because of delays in getting treatment. If the facility was in Kule, critical patients wouldn’t need to be transported and health workers could seek out serious cases. Cumbersome procedures at Ethiopian customs delay vital supplies, according to one worker.

At Kule, children entertain themselves by pulling toy lorries made from tin cans, blowing up balloons from condoms, or improvising a pool table using sticks for cues and fig cases for balls. The site is dotted with water points and pit latrines; queues are mostly short. Many families are cooking on open fires outside their tents.

The major complaint for Chuol and the other young mothers is shelter – they have one large tent between the six families. “We are facing so many challenges,” says Chuol as she swaddles a baby to her stomach. “If one child has a disease, it will contaminate the whole tent.”