The researchers took records from more than 600 rain gauges and classified each day’s rainfall on a scale from one (drizzle) to ten (a downpour).
In the late 1960s 7% of winter rain and snowfall came from the heaviest events. In the past ten years the figure has been about 12%.
There has been a similar but smaller increase in the intensity of spring rain and snowfall and a slight increase in autumnal intensity. The frequency of heavy summer rainfall seems to vary from decade to decade.
"So far it is not clear what causes these trends and variations," said researcher Douglas Maraun. "We will be looking at possible physical mechanisms and whether man-made global warming is contributing."