Long-lasting intense Cut-off Lows to become more frequent in the Northern Hemisphere

Abstract

Cut-off Lows (COLs) are mid-latitude storms that are detached from the main westerly flow. They tend to propagate slower than other mid-latitude storms and are often harbingers of heavy and persistent rainfall. The assessment of COLs in climate models is relatively limited, in fact, there are no studies conducted on the future changes of COLs within climate models. Given the importance of COLs in leading to severe hazards, here we study them in CMIP6's future (SSP5.85) simulations. The results show that COLs with high intensity and longer lifetimes are projected to become more frequent in spring over the land regions of the Northern Hemisphere. Such an increase in frequency indicates a substantial increase in related hazard as high-intensity long-lasting COLs are known to cause heavy rainfall. The effect may partly be compensated by the increasing COL propagation velocity with climate change. However, the overall increase in hazard is still high with 80% of all models indicating a surge in severe COL frequency. Lastly, the results are discussed in relation to the projected changes in COL drivers. The study forms a basis for future work on COL-associated rainfall and consequent impacts.