UC Merced

Cutoff lows (COL) are upper-level lows that are displaced from the jet stream and are often associated with a stagnant circulation that facilitates prolonged periods of precipitation and subsequent hydrologic hazards. Here, we quantify the contribution of COL to annual and seasonal precipitation totals, extremes, and hydrologic disasters across the globe, as well as explore how precipitation coincident with COL has changed in observations and is projected to change under future scenarios. Many locations received at least 20% of their annual precipitation coincident to COL across portions of the globe, with notable hotspots along the equatorward flank of the jet stream and in rain shadowed areas of the mid-latitudes. Further, regions—including the Mediterranean, southeastern Australia, the interior western United States (US), South Africa, and Northeast China—had over a third of their three-day annual maximum precipitation events coincident with COL. We also show that an estimated 6.4% of total global economic losses from flood-related disasters outside of the equatorial zone were associated with COL during 2000–2023. Significant increases in precipitation concurrent with COL occurred during 1979–2024 in portions of Europe and the northern US and southern Canada with significant declines in eastern Australia. Projections using output from the Community Earth System Model version 2 Large Ensemble show a robust increase in COL precipitation of ∼20% over the central US and eastern Europe by 2041–2070 tied to a poleward migration of the jet streams. Our results suggest that COL are an important mechanism for generating extreme precipitation and flooding impacts in many global regions, with their contribution to precipitation totals projected to rise in the coming decades in parts of the Northern Hemisphere mid-latitudes.