Rain doesn't fall just any old way. If you take records from nearly fifty thousand rain gauges scattered across the globe and compare how much water falls on a rainy day in different parts of the planet, you'll spot a surprising pattern. The shape of the graph showing how often light, moderate, and heavy rains occur turns out to be the same in the tropics, in temperate latitudes, and across different decades.
When air gets warmer, it can hold more water vapor, like a sponge that's been heated. But the rain is squeezed out of that sponge not evenly, but in bursts. Scientists found that with each degree of warming, the intensity of an individual downpour increases by about seven percent, while the number of rainy days actually decreases. So the sky stores up moisture longer, then unleashes it all at once in a powerful torrent.
This behavior is linked to how air rises during rain. Warm, moist air shoots upward faster, creating strong updrafts. These wring more water out of the cloud in a short time. But after such a downpour, the ground and plants return moisture to the air more slowly: some water runs off into rivers, some seeps deep into the soil. So the atmosphere stays "dry" longer and waits for the next refill.
This simple law (the warmer it gets, the rarer but stronger the rain) works for a single city and for the whole planet. It helps climatologists calculate more precisely where to expect floods and where to expect droughts. After all, if rains become rare and intense, infrastructure built for the old rainfall rhythm may not withstand the new downpours.
With one degree of warming, downpour intensity rises by about 7%, while the number of rainy days falls, so the total amount of water stays almost the same, but the character of rainfall changes completely.
In Kim Stanley Robinson's novel "Forty Signs of Rain," characters face the consequences of climate change: Washington is flooded by a series of unprecedented downpours — exactly the scenario described by the new study.