Tanzanian Half-Moons

Across the African Sahel, demi-lune (half-moon) rainwater-harvesting structures have become a cornerstone of landscape restoration, contributing—often together with other soil-and-water conservation measures—to the rehabilitation of hundreds of thousands of hectares: coordinated Sahel programmes reported restoring on the order of 300,000–420,000 hectares of degraded land in recent years, much of it via community-built demi-lune sites and similar catchments.

The half-moon itself is a semicircular pit roughly 2–3 m across and 0.15–0.30 m deep that traps runoff and increases infiltration, and agronomic guidance typically specifies hundreds of demi-lunes per hectare (often ~250–300) to achieve full coverage for tree or shrub planting.

Program evaluations and NGO reports note that a single trained farmer can rehabilitate about one hectare per season using mechanized or manual demi-lune construction, making the technique highly scalable when combined with initiatives like the Great Green Wall and Sahel restoration programmes.