High in la Alpujarra, on the slopes of the majestic Sierra Nevada in Andalucía, the silence is broken only by the sound of a stream trickling through the snow. Except it is not a stream but an acequia, part of a network of thousands of kilometres of irrigation channels created by Muslim peasant farmers more than a thousand years ago. The channel begins at an altitude of 1,800 metres (5,900ft) and, fed by the melting snow, for centuries supplied water to the village of Cáñar and beyond until it fell into disuse in the 1980s through the gradual depopulation of the area. Now, it is flowing again thanks to a project devised by the laboratory of biocultural archaeology at the University of Granada and backed by local and European funding. With the help of volunteers, the MemoLab project is restoring the region’s extraordinary hydrological network at a time when the climate crisis is exposing Spain to prolonged periods of drought and intensive farming is putting extreme pressure on water supplies. When Arabs and Berbers colonised Spain early in the eighth century, they brought techniques in water conservation acquired over centuries in the Middle East. “The Islamic agricultural revolution was the first green revolution. They brought together techniques and knowledge about water, soil, plants and also how snow behaves,” says José María Martín Civantos, an archaeology professor at the university and the driving force behind the project. “They transformed the way water is used in the Mediterranean.” The techniques introduced by the Muslims allowed for more agricultural diversity, with crops such as sugar cane and citrus fruits introduced. “Involving people in the creation of these irrigation systems was a way of assimilating the existing population, who could see the advantages,” adds Civantos. Rain comes to the Mediterranean in brief, torrential bursts, with the result that most of the water is lost as it runs off into rivers and the sea. The genius of the acequia system is that by controlling the flow of the water, whether from rain or snowmelt, it reduces runoff, while at the same time allowing water to be absorbed into the land to replenish the aquifers in what is literally a trickle-down effect. Civantos describes this as “sowing water”. Rather than diverting water towards specific crops, the idea is to “soak the mountain” so that water can be stored in aquifers to be used in times of drought. “The basic requirement for the system to work is that the channel isn’t too permeable and has a gradient that maintains the correct flow of water. Then you need a community of people to maintain it,” says Sergio Martos-Rosillo, a geologist involved in the project. “The system is efficient, the aquifers get replenished and no technology is required,” he says, adding that the revival of similar techniques is being explored in several Latin American countries, including Peru, and there is also interest from California where modern irrigation techniques have become unsustainable. The system in Spain “has been in use for over 1,000 years, proving its adaptability”, Martos-Rosillo says. “It’s much more manageable and adaptable than building a dam and much more resistant to climate change.” Cayetano Álvarez, president of the community of irrigators in Cáñar, is in no doubt about the impact the project has had on the village. “Everyone is obliged to maintain the channels on their land,” he says. “This project has made a big difference, but there are abandoned acequias in many other villages nearby.” The system is integrated and if land is abandoned and channels left to clog up, the water cannot flow past the blockage. So every spring, the university and villages organise groups of volunteers to clear obstructions from the acequias. “It is not just a matter of clearing away leaves and mud. We also consult with local people about how to lay the pieces of slate that line the acequias,” says José Antonio Palma García, who has been volunteering for five years. “I feel good doing this work. I feel like I am giving something back to the earth. I also meet people I’d never normally meet – we’re like a big family.” On the other side of the sierra lies the village of Alfacar, high above Granada, close to where it is widely believed fascists murdered the poet Federico García Lorca at the start of the civil war in 1936. It is also the site of a brick-walled pool of clear mountain water known as the teardrop spring. “It’s called that because of its shape,” says Elena Correa Jiménez, a researcher on the project. “The spring is supplied from an aquifer and the acequia was created 1,100 years ago to supply water to Albaicín, the medina of Granada, 8km [five miles] away.” MemoLab has restored much of the acequia and, although it doesn’t reach Albaicín, it now irrigates the university’s gardens. Civantos says one of the challenges of the project was trying to recover collective knowledge that was never written down. Due to the Catholic reconquest of Islamic Spain and the expulsion of the Muslim population early in the 17th century, much of this knowledge was lost. “People don’t think peasant farmers could devise anything this complex,” Civantos says. “The Romans built aqueducts and other waterworks but it was always for the glory of the state. This work was done so ordinary people could survive. “Recovering this system involves recognising an important part of our heritage. Muslim Spain was primarily an agrarian society. “You can’t understand the glory of Córdoba or Granada without understanding that what lay behind it was the wealth created by a form of agriculture that was much more advanced and productive than elsewhere in Europe.”