Climate change is turning snow to rain and raising risk of floods

A shift from snow to rain due to climate change is making extreme rainfall and flooding more severe in many parts of the world dominated by snow.

“We already know global warming increases total precipitation,” says Mohammed Ombadi at the Lawrence Berkeley National Laboratory in California. The atmosphere can hold about 7 per cent more water vapour for each degree Celsius of warming.

Warmer temperatures are also known to cause more snow to fall as rain. However, it wasn’t clear how this shift from snow to rain contributed to the extreme rainfall events that drive flooding and erosion, which are key factors for designing infrastructure.

Ombadi and his colleagues looked at weather records for the northern hemisphere from 1950 to 2019 to understand patterns of extreme precipitation. They also used climate models to project these patterns under different emissions scenarios.

In snowy places such as the Himalayas, the Alps and the Sierra Nevada in the US, they found the intensity of extreme rainfall increased by an average of 15 per cent for each degree Celsius of warming, more than twice the global average increase. Based on historical data and on modelling, they found that the shift from snow to rain is the main factor behind the increased extremes.