Warming has brought extreme rain to the parched Sahel, which is seeing aquifers refill as monsoons grow stronger. But heavier downpours alone cannot explain the groundwater revival, say hydrologists, who believe efforts to harvest rainfall may also be paying dividends.

After the catastrophic droughts of the late 20th century, aquifers from Senegal to Ethiopia are refilling, water tables in Niger have risen four metres, and Lake Chad has swollen to ten times its mid-1980s size. Near-extinct scimitar-horned oryx now number over 600, and farmers have nurtured 200 million trees back onto once-bare fields.