"Atmospheric rivers are projected to become more intense – in terms of water vapour transport – and more frequent in the future," David Lavers of the University of Iowa, US, told environmentalresearchweb. "This may lead to higher winter-rainfall totals, and therefore larger winter floods, associated with atmospheric river events, and more frequent flood events in the future."

Together with colleagues at the University of Reading, UK, Lavers found that in the high-emissions (RCP8.5) scenario there is an approximate doubling of atmospheric river frequency for 2074–2099 compared with 1980–2005. The researchers used simulations from five global climate models in the 5th Climate Model Intercomparison Project (CMIP5).

"As our previous research had shown a strong connection between atmospheric rivers and heavy rainfall/extreme floods in winter in Britain, it was a natural progression to ask how the flood-generating atmospheric rivers may respond to anthropogenic global warming," said Lavers. "We took the approach in the paper because we had developed an algorithm to search for atmospheric rivers in climate datasets, and the latest climate model projections (CMIP5) were starting to become available, which gave us an ideal opportunity to evaluate how atmospheric rivers were projected to change."

Atmospheric rivers are bands of intense moisture flow around 300 km wide and thousands of kilometres long, at a height of roughly 1–2.5 km. They can deliver sustained and heavy rainfall to mid-latitudes in western North America and Western Europe and often cause flooding, particularly from October to March. The atmospheric river responsible for the flooding in northwest Britain on 19 November 2009 had moisture transport that was more than 4500 times the average gauged flow in the River Thames.

The team believes its results suggest that the projected change in atmospheric rivers is predominantly a thermodynamic response to warming resulting from anthropogenic radiative forcing.

"As this work has policy relevance, one possible future research plan is to try and use this for future flood risk in areas of upland Britain," said Lavers.

Lavers and colleagues reported their work in Environmental Research Letters (ERL).

Related links

Related stories