Half of all the rain that falls on Earth in a year arrives in about nine storms, lasting a combined 28 days. That striking figure comes from researchers at Beijing Normal University in China, led by Chiyuan Miao, who studied daily records from more than 19,000 rain gauges between 1980 and 2022. The number is only the starting point, however. The more worrying discovery is that those storms are changing shape.

Since 1980, the average intense storm has become shorter by about 86 minutes per decade. Added together, the time needed to deliver half of the world's annual rainfall has fallen by just over 9.5 hours. The total amount of rain has not necessarily changed; instead, the same water is being squeezed into fewer, faster and more violent events.

The findings, published in the journal Earth's Future, show the pattern on every continent, though not evenly. Europe and South America have seen the strongest compression, with the wettest storms shortening by as much as 144 minutes a decade. Why does duration matter so much? Soil absorbs water at a limited speed, so a downpour that arrives quickly runs off the surface rather than soaking in.

That raises the risk of flash flooding and soil erosion, while the longer dry gaps between storms can deepen drought and leave vegetation more vulnerable to wildfire.