Traditional water harvesting technique revives farmland in Senegal

A traditional water harvesting method is helping to reverse decades of desertification in Senegal, turning parts of the Sahel into productive farmland once again. The initiative, backed by the United Nations World Food Programme (WFP) and local communities, forms part of the broader Great Green Wall project aimed at halting the southward expansion of the Sahara.

In Senegal’s northern Sahel region, areas previously described as “barren wasteland” after 40 years of drought and degradation are being rehabilitated using half-moon-shaped earthworks. These structures, each around four meters in diameter, are manually dug to trap rainwater and retain moisture in the soil. The technique, once widespread across the region, had largely fallen out of use.

“This is nothing new—we have not invented a technology here,” said Sebastian Muller from the WFP’s resilience team. “The half moon technology is actually an endogenous technology to the Sahel and has been forgotten over time. We have rescued it from the past.”

The half-moons help improve water infiltration, with 10% to 15% of the retained water seeping into the ground and recharging local aquifers. Their use also allows drought-resistant crops such as millet, sorghum, okra, and tomatoes to be cultivated once again.

According to Andrew Millison, a permaculture expert and instructor at Oregon State University, the broader context of this effort is critical. The Sahara has expanded by an estimated 10% over the past century, and the Great Green Wall—launched in 2007—aims to create an 8,000-kilometre belt of vegetation across the continent to stem that advance.

In a February 2024 video report, Millison highlighted a project in Senegal where 300,000 hectares of land are being restored. The work is community-driven, starting with local consultations and planning.

“By the end of this process, it was agreed that one of the major actions is the land reclamation or land recovery project,” said Bakalilou Diaby, a program policy officer with the WFP.

Muller noted that the initial challenge was convincing villagers that regeneration was feasible. “After learning about how to improve the land, the people believe and they are convinced, and they are also committed,” Diaby said.

The project combines traditional techniques with modern ecological methods. Alongside half-moon water catchments, the initiative uses horizontal horticultural beds and syntropic farming—an agroecological approach developed in Brazil that mimics natural forest growth patterns. Fruit trees are planted in trenches between vegetable beds to support long-term soil health and food production.

“This project was really, really interesting because the World Food Programme wanted to demonstrate how you could take the most devastated areas and turn them back into resilient, food-producing locations,” said Millison.

The revival of half-moon cultivation and other regenerative methods offers a model for reclaiming degraded lands across Africa’s drylands. Proponents argue that community-led strategies rooted in local knowledge are key to ensuring both food security and climate resilience in the face of ongoing environmental change.