She points a rough finger at a line of dead trees, half-buried in sand, planted years ago as part of her 20-year losing battle to halt the once-distant dunes which now threaten to spill into her onion crop.

"It moves very fast, much faster than anything I can do to stop it," said Ma, 60.

Ma is on the front lines of a national struggle against a relentless foe: desertification.

An ancient oasis in destitute Gansu province along the historic Silk Road, Dunhuang is in danger of being swallowed by the sands of the adjacent Kumtag desert, which are creeping closer at a rate of up to four metres (13 feet) a year.

The city's plight starkly illustrates the threat of desertification and the hard choices it presents to tens of millions of people living across northern and western China.

About 2.6 million square kilometres (one million square miles) were classified as desert wasteland in the most recent government survey in 2004, up more than 50 percent in a decade and challenging China's ability to feed its 1.3 billion people.

The problem stems from centuries of unsustainable grazing and farming practices and overuse of already slim and strained water resources.

The government has attempted to blunt the spread through reforestation, incentives and other means, said Greenpeace China climate change campaigner Li Yan.

But the hotter, drier climate due to global warming poses a renewed threat, she adds.

"This is already a serious problem for China, and Greenpeace is extremely worried that climate change will worsen it," she said.

Once a welcome oasis for Silk Road travelers thanks to an ancient store of groundwater, Dunhuang is drying up.

The water table in the city of 100,000 has dropped 12 metres (39 feet) since 1975 and is still falling as city growth strains the water supply, according to official figures.

Its rivers and lakes have shrunk 80 percent in 30 years while the Kumtag dunes creep closer as vegetation that restrained the sands for aeons dies out.

-- "This is Mother Nature's way of punishing us" --

"It's a very complicated issue that shows we have ignored the environment too much in the past," Mayor Sun Yulong told AFP.

"Now, changes are occurring. This is mother nature's way of punishing us."

Sandstorms -- higher in number and intensity -- also have accelerated the deterioration of the 1,000-year-old Buddhist frescoes at Dunhuang's Mogao caves, one of China's great historical sites and a growing tourist draw for the traditionally agrarian community.

Chinese Premier Wen Jiabao called recently for renewed efforts to prevent Dunhuang becoming "a second Loulan," referring to another Silk Road stop further west that was swallowed by the desert in the last century.

Dunhuang, where large ubiquitous signs urge water conservation, has moved aggressively, placing tight restrictions on all new inward migration, wells and farms.

But the impact on residents has been harsh.

Standing amid his withering cotton fields, 64-year-old Dai Nianzuo said tough water rationing has dramatically reduced yields.

The 3,000 yuan (400 dollars) he used to make each year from his crops has been slashed to about 1,200 yuan.

"The situation is very bad for us and the government does not have an answer," he said, holding a tattered burlap bag full of freshly picked cotton.

Greenpeace's Li commends official efforts so far but says authorities must make the issue -- and especially the climate change impact -- a higher priority.

Greenpeace recommendations include incentives to develop wind power in threatened areas so that precious vegetation is not harvested for use as fuel, and taking biodiversity into account when selecting tree species for reforestation.

"If we don't stress climate change in the overall plan, that could make for a very unpleasant future," Li said.

Ma, the onion farmer, hopes to turn the situation to her advantage by turning her property into a tourist stop for the growing numbers of visitors coming to hike the majestic Kumtag dunes.

But the government has placed restrictions on operations such as these, too.

"I need money to start something like that but the government gives me no support," she said, her feet crunching along in the sand.

"It's a big problem."

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