As the climate heats up, the forecast is also calling for more rain. Think downpours. Cats and dogs. Or just "extreme rain", as the scientists call it.

The overall rain and snowfall average is increasing only moderately. But observations since 1951 show the wettest days every year have built up their intensity by 1 per cent to 2 per cent per decade, according to a study published this week in the journal Nature Climate Change.

The heavy precipitation is increasing over both wet and dry land areas, a surprising conclusion drawn from the research.

A mantra among climate scientists for years has held that, as humanity continues to pump out carbon pollution, regions with lots of rainfall will receive more, and relatively arid places will get even less. That's a global projection, however, and most of the globe's surface consists of ocean. More recently, scientists have wondered if that will hold true over land as well.

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The Australian and United States scientists who conducted the new study conclude that it may not hold true.

The skies are dumping more and more water on land, regardless of traditional, local climatic conditions.

The basics of the Earth's water cycle are pretty straightforward. When it's warmer, water not only evaporates faster, but the air can hold more moisture. So when storms come, there's more water vapour to tap, and down it comes.

Places that are already built to withstand heavy rainfall have a head start over drier neighbours, the authors wrote, a fact that informs their main policy suggestion: Dry regions should implement new protective measures against extreme rainfall because "even small increases in the intensity of extremes can have strong impacts".

The forecast for climate-change and flood-protection measures is cloudy at best.