On nights when the wind hisses across the dunes, the old man sits on his straw mat, draws a blanket around his shoulders and counts his dwindling money.
In the morning, Sidahmed Ould Magaya, 75, will be trapped inside his concrete one-room house, the wooden door sealed shut by a wall of sand accumulated overnight. In exchange for about $6, workers will liberate him, hauling the yellow sand away in burlap bags.
At that rate, he has to sell a goat a month to pay for keeping the desert at bay in a country where the dunes are said to be shifting at an estimated 4 to 6 miles per year, according to government data.
Throughout Mauritania, a desolate, dune-enveloped country twice the size of France, men and women wage a daily battle against the sand.
With less rain falling now than in years past, the dunes have become dry and unstable. Global climate change bears part of the blame, as does the uprooting of the scraggly trees that once dotted the landscape to use as camel feed, firewood or for insulation, leaving nothing to bind the sand.
When the winds whip the land, the dunes advance like fingers, overtaking walls, forcing their way into courtyards and creeping under doors. Whole houses are swallowed. Entire cities have been abandoned.
“When I built my house, I chose this spot because it was flat. Now there’s a mountain outside,” said Mr. Magaya of his house, currently free of sand but precariously positioned at the edge of an advancing dune. His front door opens onto the face of the dune, which rises sharply upward and crests just above the roof from where it bears down on the old man like a yellow giant.
A wave of sand has crashed into his neighbor’s home, swallowing the front door, forcing the family to use the back entrance. In the towns under the most sand, families go in and out of their windows. Snowplows crisscross the national highway, pushing sand aside to let cars through.
Europe and North America have hurricanes, floods and snowstorms; the nations lying across the Sahara — Mauritania, Mali, Niger, Chad and the southern edges of Libya, Algeria and Egypt — have sand, and a warming planet is making it less predictable.
Surface temperatures have risen by a little over 1 degree Fahrenheit in the last century, said Patrick Gonzalez, a climate scientist on the U.N.’s Intergovernmental Panel on Climate Change. The rise in the temperature of the Earth, as well as of the Atlantic Ocean bordering Mauritania, has had an impact on rainfall: It’s down a fifth from the 1950s.
Without moisture to keep the sand in clumps, it moves freely, dissipating in a yellow mist.
“It’s a vicious cycle, brought on by the changes in our climate and worsened by the actions of mankind,” said Moustapha Ould Mohamed, who heads the National Research Center on Desertification in Nouakchott, the Mauritanian capital.
Although it is now illegal to cut much of the vegetation, desert dwellers refuse to live without some plants — for example alfa, a shrub used as roof insulation. Those living here say they often see donkeys coming into town laden with alfa.
“The battle against the dunes cannot be uncoupled from the battle against poverty. If these people don’t have an alternative, they will continue to cut the trees,” said Mohamed Lemine Ould Cheikh El Hadrami, Mauritania’s environment secretary.
In a 109-page national action plan written by the ministry last year, the Mauritanian government proposed a series of measures from the creation of a green belt around threatened cities to planting sticks in formations that halt the flow of sand.
Although commissioned by the government, the plan gets no funding in Mauritania’s current budget, underscoring an inability to grasp the threat, said Mounkaila Goumandakoye, the acting director of the U.N. Development Program’s Drylands Development Center.
“What’s happening in Mauritania is dramatic, and something needs to be done,” he said. “Politicians are used to doing things to improve their country’s [gross domestic product]. They haven’t yet understood the link between the advance of the dunes and their economic health.”
In the arid interior, where the dunes undulate like the surface of the sea, that link is all too obvious.
Dates are the backbone of the desert economy, but cones of sand now surround some of the oldest palm trees, and once the cone reaches the fronds, the tree suffocates.
As recently as 1960, the town of Chinguetti had 18 square miles of date-bearing palms.
“Now, not even [5 acres] remain,” said Mayor Mohamed Ould Amara.
The town, on an ancient caravan route, was Mauritania’s most populous with a population of 20,000 in the 19th century, and it’s now down to 3,000, he said, adding that over 300 of its 1,000 homes have been abandoned.
“We’re under an ocean of sand,” the mayor said.
Among the palms still standing are a dozen or so owned by Mr. Magaya. He’s running out of goats to sell each time his door needs digging out, and counts on the palms to finance his old age at the foot of the yellow-colored dune.
He takes comfort in the fate he knows awaits him, whether or not the dune gets to him first.
“When I die, I’ll be put in a coffin, and that coffin will be buried in the sand,” he said. “So I can’t be upset. Either way, I’ll end up in the dirt.”