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

A shift from snow to rain because of local weather change is making excessive rainfall and flooding extra extreme in lots of elements of the world dominated by snow.

“We already know global warming increases total precipitation,” says Mohammed Ombadi on the Lawrence Berkeley National Laboratory in California. The environment can maintain about 7 per cent extra water vapour for every diploma Celsius of warming.

Warmer temperatures are additionally identified to trigger extra snow to fall as rain. However, it wasn’t clear how this shift from snow to rain contributed to the acute rainfall occasions that drive flooding and erosion, that are key components for designing infrastructure.

Ombadi and his colleagues checked out climate data for the northern hemisphere from 1950 to 2019 to know patterns of utmost precipitation. They additionally used local weather fashions to venture these patterns below completely different emissions eventualities.

In snowy locations such because the Himalayas, the Alps and the Sierra Nevada within the US, they discovered the depth of utmost rainfall elevated by a median of 15 per cent for every diploma Celsius of warming, greater than twice the worldwide common improve. Based on historic information and on modelling, they discovered that the shift from snow to rain is the principle issue behind the elevated extremes.

“We are already seeing that in the data,” says Ombadi. He factors to the flooding in California this yr and the devastating floods in Pakistan in 2022 as examples the place extra rain within the mountains might have performed a task in flooding downstream.

Frances Davenport at Colorado State University says her analysis has discovered rain-driven floods in some areas have been greater than twice as massive as floods pushed by snow that melted on the bottom, although the hyperlink between rainfall and flood threat is advanced. “We’re still in a climate where we get both snow and rain, and the fraction can vary a lot,” she says.

Jouni Räisänen on the University of Helsinki in Finland provides that the impact would possibly seem much less pronounced if considered in proportion to native will increase in temperature, fairly than international averages, for the reason that temperature rises over land are typically increased. But he expects extra excessive rainfall in any case. “This makes very good sense to me,” he says.