Unmitigated climate change will cause substantial increases in large-scale rainfall events in Europe and North America, according to researchers from the UK.
The analysis suggests that policy makers could need to develop new management strategies “to take into account the changing frequency and intensity of these events”, says Matt Hawcroft of the University of Exeter, UK.
Warmer climates are expected to deliver precipitation extremes of greater frequency and intensity. Precipitation intensity is a product of the Clausius–Clapeyron relation, which describes how much more water the atmosphere can hold as its temperature increases. But the relation is a simple scale that gives little indication where new intense precipitation will occur.
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Unfortunately for climate modellers, there are many competing processes that determine the paths storms travel, including equator-to-pole temperature gradients, sea-ice loss, sea-surface temperature patterns and land-sea temperature contrasts, not to mention feedbacks from the storms themselves. The result at present is a large uncertainty in where storms will move under climate change.
Yet Hawcroft and his colleagues at Exeter and the University of Reading, UK, believe it is still possible to gain an insight into the nature and frequency of extreme precipitation changes at the regional level — by analysing the behaviour of the storms themselves in Europe and North America in simulations of both present-day climate and climate change under unmitigated greenhouse-gas emissions.
The team used an algorithm that seeks out vortices to identify storms in their models so that they could assign precipitation to individual events. Then they compared the number and intensity of the cyclones in the present-day and future climate-change simulations.
Hawcroft and colleagues found a big increase in the frequency of extreme extratropical cyclones, with above today’s 99th percentile of precipitation intensity, by the end of the century under unmitigated climate change; the number of extratropical cyclones delivering such intense rainfall more than tripled.
“Even with this uncertainty [in the underlying storm paths], there is quite a lot of consistency in the increase in extreme-storm-associated precipitation,” says Hawcroft.
Hawcroft is now exploring the dynamics that drive inter-annual and sub-seasonal variability in storms producing extreme rainfall, and how those dynamics could change in a warmer climate. The team reported the findings in Environmental Research Letters (ERL).
