Fewer deep cyclones projected for the midlatitudes in a warming climate, but with more intense rainfall

Abstract

Cyclones are a major cause of extreme weather in the extratropics. Projections of future climate change have focussed on extratropical cyclones identified close to the surface, but cyclones identified at multiple levels of the atmosphere (‘deep’ cyclones) make the largest contributions to total and extreme rainfall. Here we use ten CMIP5 models to assess projected changes in cyclone frequency and associated heavy rainfall between 1979–2005 and 2070–2099 under a high emissions scenario (RCP8.5), with a focus on changes in vertically organised (‘deep’) systems with cyclones present at both the surface and 500 hPa. We find a robust decrease in the number of deep cyclones by the end of the 21st century, together with an increase in the number of extreme rainfall events caused by deep cyclones. In contrast to deep cyclones, shallow cyclones identified only at the surface are found to produce less rain and are projected to increase in frequency in the future, particularly over land areas. Our findings demonstrate the benefits of considering vertically deep cyclones, as their connection to extreme rainfall has implications for risk assessment and climate adaptation strategies.