VIRU, Peru — The desert blooms now. Blueberries grow to the size of Ping-Pong balls in nothing but sand. Asparagus fields cross dunes, disappearing over the horizon.

The desert produce is packed and shipped to places such as Denmark and Delaware. Electricity and water have come to villages that long had neither. Farmers have moved here from the mountains, seeking new futures on all the irrigated land.

It might sound like a perfect development plan, except for one catch: The reason so much water flows through this desert is that an ice cap high up in the mountains is melting away.

And the bonanza might not last much longer.

“If the water disappears, we’d have to go back to how it was before,’’ said Miguel Beltrán, a 62-year-old farmer who worries what will happen when water levels fall. “The land was empty, and people went hungry.’’

In this part of Peru, climate change has been a blessing — but it might become a curse. In recent decades, accelerating glacial melt in the Andes has enabled a gold rush downstream, contributing to the irrigation and cultivation of more than 100,000 acres since the 1980s.

Yet the boon is temporary. The flow of water is already declining as the glacier vanishes, and scientists estimate that by 2050 much of the ice cap will be gone.

Throughout the 20th century, enormous government development projects, from Australia to Africa, have diverted water to arid land. Much of Southern California was dry scrubland until canals brought water, inciting a storm of land speculation and growth — a time known as the “Water Wars’’ depicted in the 1974 film “Chinatown.’’

Yet climate change now threatens some of these ambitious undertakings, reducing lakes, diminishing aquifers, and shrinking glaciers that feed crops. Here in Peru, the government irrigated the desert and turned it into farmland through an $825 million project that, in a few decades, could be under serious threat.

“We’re talking about the disappearance of frozen water towers that have supported vast populations,’’ said Jeffrey Bury, a professor at the University of California, Santa Cruz who has spent years studying the effects of glacier melt on Peruvian agriculture. “That is the big-picture question related to climate change right now.’’

A changing climate has long haunted Peru. One past civilization, the Moche people, built cities in the same deserts, only to collapse more than a millennium ago after the Pacific Ocean warmed, killing fish and causing flash floods, many archeologists contend.

Now dwindling water is the threat. While more than half of Peru sits in the wet Amazon basin, few of its people ever settled there. Most inhabit the dry northern coast, cut off from most rain by the Andes range.

While the region includes the capital, Lima, and 60 percent of Peruvians, it holds only 2 percent of the country’s water supply.

The glaciers are the source of water for much of the coast during Peru’s dry season, which extends from May to September. But the ice cap of the Cordillera Blanca, long a supply of water for the Chavimochic irrigation project, has shrunk by 40 percent since 1970 and is retreating at an ever-faster rate. It is currently receding by about 30 feet a year, scientists say.

Farmers along the 100-mile watershed that winds its way from the snowcapped peaks to the desert dunes say they are already feeling the effects of the change.

The retreat of the ice cap has exposed tracts of heavy metals, like lead and cadmium, that were locked under the glaciers for thousands of years, scientists say. They are now leaking into the ground water supply, turning entire streams red, killing livestock and crops, and making the water undrinkable.

Temperatures in this area have risen sharply, leading to strange changes in crop cycles, farmers say. Over the past decade, corn — which since precolonial times was grown only once a year in the mountains — can now be harvested in two cycles, sometimes three.

That would be a windfall, farmers like Francisco Castillo said, if it were not for all the pests that now thrive in the warmer air.

For Castillo, who plants corn and rice near the Santa River in Chimbote, it was a worm that became the scourge for him and neighboring farmers. It suddenly started devouring their crops in the early 2000s.

Then, last year, came the rats. “This wasn’t a place you had rats before,’’ Castillo said.

The Chavimochic project, which lies just north of where the Santa River meets the Pacific Ocean, is a crown jewel of Peruvian agriculture and civil engineering.

The government aimed to create industrial-scale agriculture in Peru’s northern deserts through a sprawling system of locks and canals. The idea’s supporters promised profits through exports to markets in North America, Asia, and Europe, where the fruit seasons were reversed.

The first phase of the project started in 1985 with a 50-mile canal that irrigated a valley and brought a large hydroelectric plant, providing electricity to residents.