By Seth Mydans Cai Rang, Vietnam
FOR centuries, as monsoon rains, typhoons and wars have swept over them to disappear in the sunshine, the farmers and fishermen of the Mekong Delta have drawn life from the water and fertile fields where the great river ends its 2,700-mile journey to the sea.
But everything here, both the timeless and the new, is at risk now from a threat that could bring deeper and longer-lasting disruptions than the generations of warfare that ended more than 30 years ago.
In a worse-case projection, a Vietnamese government report released last month says that more than one-third of the delta, where 17 million people live and nearly half the country's rice is grown, could be submerged if sea levels rise by 3ft in the decades to come.
In a more modest projection, it calculates that one-fifth of the delta would be flooded, said Tran Thuc, who leads Vietnam's National Institute for Hydrometeorology and Environmental Sciences and is the chief author of the report.
Storm surges could periodically raise that level, he said, and experts say an intrusion of salt water and industrial pollution could contaminate much of the remaining delta area.
The risks of climate change for Vietnam go far beyond the Mekong Delta.
Climate experts consider this nation of an estimated 87m people to be in the top five most threatened by rising sea levels linked to climate change.
If the sea level rises by 3ft, 11 per cent of Vietnam's population could be displaced, according to a 2007 World Bank working paper. If it rises by 15ft, 35 per cent of the population and 16 per cent of the country's land area could be affected, the document said.
The potential disruptions and the tremendous cost of trying to reduce their impact could slow Vietnam's drive to emerge from its postwar poverty and impede its ambitions to become one of the region's economic leaders.
Once again, this nation, which has spent much of its history struggling to free itself from foreign domination, finds itself threatened by an overpowering outside force.
"Climate change isn't caused by a developing country like Vietnam, but it is suffering the consequences," said Koos Neefjes, a policy adviser on climate change with the United Nations Development Programme in Hanoi.
In addition to rising seas in the Mekong Delta, climatologists predict more frequent, severe and southerly typhoons, heavier floods and stronger storm surges that could ultimately drive hundreds of thousands of people from their homes.
Climate refugees could swell the population of Ho Chi Minh City, on low-lying land just north of the delta, as war refugees did when it was known as Saigon.
But the city itself is also at risk, says the government study, prepared by the Ministry of Natural Resources and Environment. Up to a quarter of the city's area would be threatened by rising floodwaters if the sea level were to rise by 3ft.
"Ho Chi Minh City could have a double impact if sea levels rise and living conditions in the delta are not sustainable," Thuc, the lead author of the government report, said.
His report assesses only the climatological risks, he added, and a great deal more work needs to be done to try to determine their social and economic impacts and the probable effect on future population displacement.
Because of the uncertainties of climate change and the variables of mitigation measures, it is impossible to rank nations precisely on a scale of risk, Neefjes said.
"Among all of the indicators used in this paper, Vietnam ranks among the top five most impacted countries," the paper says. It did not include some small island nations such as the Maldives and Tuvalu that are also threatened with severe inundation.
A report by the Intergovernmental Panel on Climate Change listed the Mekong Delta, Bangladesh and the Nile Delta in Egypt as the world's three "hot spots" for potential migration because of their combination of sea-level rise and existing population.
As a region, Southeast Asia is disproportionately vulnerable, with only 3.3 per cent of the world's land mass but more than 11 per cent of its coastline, the Asian Development Bank said in a report it released earlier this year.
But Vietnam has at least recognised the problem and has begun to address it, Neefjes said. "Faster than any developing country, it has actually developed a sensible national programme to start responding," he said.
Those plans include an attempt to integrate environmental concerns into the development plans of ministries and enterprises, modifications that could conflict with their ambitions for growth, he said.
Experts said Vietnam's primary approach – the hugely expensive construction and reinforcement of thousands of miles of dikes – would bring its own set of problems.
In the delta, they said, the barriers will probably inhibit the self-cleansing mechanism of rivers and trap millions of cubic yards of industrial waste, hundreds of thousands of tons of industrial rubbish, and millions of tons of pesticides and fertiliser that are used in fish farms and shrimp farms.
"If one-third of the delta's area is flooded by seawater, losses would be huge," Vo Hung Dung, director of the Chamber of Commerce and Industry's Can Tho city branch, said last month in the newspaper Tuoi Tre. "But if the entire delta is polluted by waste water, the losses could be many times higher."
Here on the tiny Hau River,
Nguyen Thanh Chanh, 29, who fishes with his wife in a small boat, said that he had never heard any talk of climate change.
Life is already hard, and the rivers already flood during the monsoon season from June to November.
"Those who farm go to the fields, and those who fish go to the rivers," said Huynh Thuy, 47, a farmer.
"They don't worry much about the future."