When the first white cranes started appearing on the banks of the Rio Coco, deep in the Nicaraguan rainforest, Marciano Washington told his sons to start preparing the family's three hectares of land for planting.

A month later, the weather-beaten Miskito elder from the town of San Carlos shades his eyes from the baking sun and surveys his cracked and barren land. His seed is rotting or has been eaten by rats. The few rice seeds that have sprouted are only inches high, yellow and discoloured.

"All my life the earth has told me when the rains are coming," he says. "I don't understand what is happening to our land."

The natural signs that Washington's father taught him to observe, such as the white cranes, flowering avocado plants, silver fish and rapid flashes of lightning, no longer herald the rains that his community so desperately needs.

Climate change is having a devastating effect on the Miskito Indians who live in wooden huts in Nicaragua's western territories. They subsist on crops planted on a few hectares of land and on food hunted from the jungle and rivers.

Ten years ago Washington said he could harvest 60 bags of rice a hectare. Last year he managed seven. "Every year it is getting worse," he says. "We have floods in the summer and droughts in the winter. We can't depend on nature anymore and we don't know when to plant our crops. I don't know how I am going to feed my family."

Environmental researchers are warning that the effect of climate change is likely to hit indigenous communities like the Miskito the hardest. Many of the world's indigenous people live in isolated communities and their livelihoods depend on nature and on predicting the weather, making them vulnerable to increasingly unstable weather patterns.

In a report published on May 29, Oxfam International says that at least $50 billion (£25 billion) a year in addition to existing aid budgets is needed to help communities like the Miskito adapt to climate change.

In the report, Oxfam says that those governments with a legacy of high carbon emissions and the means to support the indigenous communities suffering the impact of climate change should foot the majority of the bill, with the US, Europeans and Japanese contributing 75% of the total.

"Western governments need to understand the scale of the threat and take preventive action," says Kate Raworth, author of the report, Adapting to Climate Change. "Otherwise we will all face huge costs in cleaning up after the increasingly large-scale disasters that will be the inevitable consequence of the inability of developing communities to adapt to climate change."

Scientists are painting a bleak picture for the future of Nicaragua's indigenous communities. Temperatures across Central America are expected to rise by 1° to 3° centigrade, and rainfall will decrease by 25% by 2070. Droughts, hurricanes and unseasonal flooding are just a few of the expected consequences of such a rapidly changing climate.

Isolated from modern farming techniques and crippled by poverty after years of economic neglect and discrimination, the Miskito are on the frontline. They make up the majority of Nicaragua's 85,000-strong indigenous population. By now they should have had almost three weeks of heavy rain, but the Miskito villages perched on the banks of the Rio Coco, the 470-mile [760-kilometre] river that snakes through Nicaragua's indigenous territories, are baking under temperatures higher than 40° C [104° F].

After centuries defending their rainforest territories from Spanish settlers, Sandinista guerrillas and US-backed Contra forces, they lack the knowledge or resources to deal with the greatest threat to their survival yet.

"We are a proud people. Do you think we want to have to ask for help or depend on handouts from outside agencies?" says Nicanor Rizo, a community leader in Riati, the oldest Miskito community on the Rio Coco. "This is our land and we are unable to fulfil the responsibility passed down to us by our elders to protect and look after the river and the forest."

Almost a month into the rainy season, the river should be a swirling torrent. But at many points the water is ankle-deep and dugout boats struggle to negotiate their way upstream.

In the village of Siksayari, home to 1,400 Miskito, Martine Valle, a technician from the ministry of agriculture who is volunteering in the village, explains that the people there have been without basic supplies such as salt and drinking water for more than a month. "The situation is getting desperate," he says. "There are no roads here. Nobody expected the river to dry up and now supply boats can't get down here. At the moment the water is too polluted and diseases like cholera and TB are rising."

Many Miskito communities believe the massive deforestation of their territories -- an estimated 50% of its rainforest has been felled in the last 50 years -- is also having a detrimental effect. Last year the new government of President Daniel Ortega pushed through a speedy logging ban to halt deforestation. But with no effective policing of the ban, local non-governmental organisations say that it has pushed commercial logging operations deeper into the forest.

Around 80% of Nicaragua's natural resources are to be found within the Miskito territories. Although the Unesco-designated Bosawas Biosphere Reserve protects 1.8 million acres of forest, the exploitation of their land continues.

Last year Nicaraguan media reported that contracts had been signed between the previous government and two multinational companies for the exploitation of oil and natural gas on indigenous lands in Bilwi, in the Puerto Cabezas municipality. Community elders in Wiwinak, a small village of 120 families, say their wells have also been contaminated by cyanide and mercury from the new gold mines along the river.

Weather monitoring stations installed by Oxfam along the banks of the Rio Coco help Nicaragua's indigenous people deal with the impact that increasingly unpredictable weather patterns are having on their way of life. But the long-term ability of the Miskitos to adapt is looking increasingly uncertain.

"We feel we can't be the guardians of the land like our ancestors anymore and we don't know what to teach our children," says Nicanor Rizo. "The world has changed and we know that we will somehow have to change with it if we want to survive."

At risk: Other communities on the frontline of climate change

* In the Canadian Arctic, western Inuit are having trouble reaching their traditional hunting grounds as warmer springs have brought an earlier thaw. Inuit campaigners say their human rights are being violated by human-induced climate change

* In Norway, Sami reindeer hunters have recorded severe changes in weather patterns that are affecting breeding cycles and destroying grazing areas. The Sami are having to alter their travel routes because of changes to prevailing winds previously used for navigation

* Residents of the Pacific island nation of Tuvalu claim to be the first climate change refugees, as many have been forced to flee to neighbouring New Zealand to escape rising seas. The islands, only three feet (one metre) above sea level, are expected to disappear below the waves

* Indigenous communities in Puerto Rico have seen plants they gather for traditional medicines disappear, making it impossible to continue healing practices

* Severe droughts are forcing the nomadic Turkana people of north-west Kenya into towns and relief camps as entire herds of camels, cows and goats are being wiped out. Although they are accustomed to months of dry weather and resulting food shortages, droughts are becoming more intense and more frequent