We met Isaac and Abdi, Alima and Muslima last week in the bone-dry, stony land close to the Ethiopia-Kenya border. They were with five nomad families who have watched all their animals die of star vation this year in a deep drought, and who have now decided their days of herding cattle are over.

After three years of disastrous rains, the families from the Borana tribe, who by custom travel thousands of miles a year in search of water and pasture, have unanimously decided to settle down. Back in April, they packed up their pots, pans and meagre belongings, deserted their mud and thatch homes at Bute and set off on their last trek, to Yaeblo, a village of near-destitute charcoal makers that has sprung up on the side of a dirt road near Moyale. Now they live in temporary "benders" – shelters made from branches covered with plastic sheeting. They look like survivors from an earthquake or a flood, but in fact these are some of the world's first climate-change refugees.

For all their deep pride in owning and tending animals in a harsh land, these deeply conservative people expressed no regrets about giving up centuries of traditional life when we spoke to them. Indeed, they seemed relieved: "This will be a much better life," said Isaac, a tribal leader in his 40s. "We will make charcoal and sell firewood. Our children will go to the army or become traders. We do not expect to ever go back to animals."

They are not alone. Droughts have affected millions in a vast area stretching across Kenya, Somalia, Ethiopia, Eritrea, Sudan, Chad, and into Burkina Faso and Mali, and tens of thousands of nomadic herders have had to give up their animals. "[This recent drought] was the worst thing that had ever happened to us," said Alima, 24. "The whole land is drying up. We had nothing, not even drinking water. All our cattle died and we became hopeless. It had never happened before. So we have decided to live in one place, to change our lives and to educate our children."

Parched

Kenya, a land more than twice the size of Britain, is everywhere parched. Whole towns such as Moyale with more than 10,000 people are now desperate for water. The huge public reservoir in this regional centre has been empty for months and, according to Molu Duka Sora, local director of the government's Arid Lands programme, all the major boreholes in the vast semi-desert area are failing one by one. Earlier this year, more than 50 people died of cholera in Moyale. It is widely believed that it came from animals and humans sharing ever scarcer water.

Food prices have doubled across Kenya. A 20-litre jerrycan of poor quality water has quadrupled in price. Big game is dying in large numbers in national parks, and electricity has had to be rationed, affecting petrol and food supplies. For the first time in generations there are cows on the streets of Nairobi as nomads like Isaac come to the suburbs with their herds to feed on the verges of roads. Violence has increased around the country as people go hungry.

"The scarcity of water is becoming a nightmare. Rivers are drying up, and the way temperatures are changing we are likely to get into more problems," said Professor Richard Odingo, the Kenyan vice-chair of the UN's Intergovernmental Panel on Climate Change (IPCC).

"We passed emergency levels months ago," said Yves Horent, a European commission humanitarian officer in Nairobi. "Some families have had no crops in nearly seven years. People are trying to adapt but the nomads know they are in trouble."

Many people, in Kenya and elsewhere, cannot understand the scale and speed of what is happening. The east African country is on the equator, and has always experienced severe droughts and scorching temperatures. Nearly 80% of the land is officially classed as arid, and people have adapted over centuries to living with little water.

There are those who think this drought will finish in October with the coming of the long rains and everything will go back to normal.

Well, it may not. What has happened this year, says Leina Mpoke, a Maasai vet who now works as a climate change adviser with Ireland-based charity Concern Worldwide, is the latest of many interwoven ecological disasters which have resulted from deforestation, over-grazing, the extraction of far too much water, and massive population growth.

"In the past we used to have regular 10-year climatic cycles which were always followed by a major drought. In the 1970s we started having droughts every seven years; in the 1980s they came about every five years and in the 1990s we were getting droughts and dry spells almost every two or three years. Since 2000 we have had three major droughts and several dry spells. Now they are coming almost every year, right across the country," said Mpoke.

He reeled off the signs of climate change he and others have observed, all of which are confirmed by the Kenyan meteorological office and local governments. "The frequency of heatwaves is increasing. Temperatures are generally more extreme, water is evaporating faster, and the wells are drying. Larger areas are being affected by droughts, and flooding is now more serious.

"We are seeing that the seasons have changed. The cold months used to be only in June and July but now they start earlier and last longer. We have more unpredictable, extreme weather. It is hotter than it used to be and it stays hotter for longer. The rain has become more sporadic. It comes at different times of the year now and farmers cannot tell when to plant. There are more epidemics for people and animals."

'We have to change'

Mpoke said he did not understand how people in rich countries failed to understand the scale or urgency of the problem emerging in places such as Kenya. "Climate change is here. It's a reality. It's not in the imagination or a vision of the future. [And] climate change adds to the existing problems. It makes everything more complex. It's here now and we have to change."

The current drought is big, but the nomads and western charities helping people adapt say the problem is not the extreme lack of water so much as the fact that the land, the people and the animals have no time to recover from one drought to the next. "People now see that these droughts are coming more and more frequently. They know that they cannot restock. Breeding animals takes time. It take several years to recover. One major drought every 10 years is not a problem. But one good rainy season is not enough," said Horent.

Nor are traditional ways of predicting and adapting to drought much use. In the past, said Ibrahim Adan, director of Moyale-based development group Cifa, nomads would look for signs of coming drought or rain in the stars, in the entrails of slaughtered animals or in minute changes in vegetation. "When drought came, elders would be sent miles away to negotiate grazing rights in places not so seriously hit, and cattle would be sent to relatives in distant communities. People would reduce the size of their herds, selling some and slaughtering the best to preserve the best meat to see them through the hard times. None of that is working now."

Francis Murambi, a development worker in Moyale, said: "The land has changed a lot. Only 60 years ago, the land around Moyale was savannah with plenty of grass, big trees and elephants, lions and rhino." Today the grasses have all but gone, taken over by brush. Because there are fewer pastures, they are more heavily used. It's a vicious circle. In the past, a nomadic family could live on a few cows which would provide more than enough milk and food. Now the pasture is so poor that those who still herd cattle need more animals to survive. But having more cattle further degrades the soil. The environment can support fewer and fewer people, but the population has increased.

"[Before] we did not need money. The pasture was good, the milk was good, and you could produce butter. Now it is poor, it is not possible," said Gurache Kate, a chief in Ossang Odana village near the Ethiopian border. "Yesterday I had a phone call from the man we sent our cattle away with. He is 250 miles away and he said they were all dying."

These shifts driven by climate change are bringing profound changes. Ibrahim Adan said: "The cow has always been your bank. Being a Borana means you must keep livestock. It's part of your identity and destiny. It gives you status. Traditionally livestock was central to life. The old people saw cattle as the centre of their culture. Pride, love and attachment to cattle was all celebrated in song. My father would never sell cattle. They were an extension of himself."

Now, for people like Isaac and Abdi, Alima and Muslima, all that is gone, and with it independence and self-sufficiency. "The money economy is creeping in, as is education and the settled life," said Adan. "Young people see the cow now as more of an economic necessity rather than the core of their culture."

The great unspoken fear among scientists and governments is that the present cycle of droughts continues and worsens, making the land uninhabitable. "This isn't something that will just affect Kenya. What is certain is that if climate change sets in and drought remains a frequent visitor, there will be far fewer people on the land in 20 years," said Adan. "The nomad will not go. But his life will be very different."