A Decomposition of the Key Drivers of Current and Future Northern Hemisphere Cyclone-Associated Precipitation Trends

Abstract Extratropical cyclones are responsible for most precipitation falling north of 40°N, especially in winter. Greater moisture availability in a warmer world is expected to boost the intensity of cyclone-associated precipitation (CAP), but how changes in cyclone frequency and intensity impact this trend is uncertain. Here, we use two atmospheric reanalyses and 18 climate models participating in phase 6 of the Coupled Model Intercomparison Project (CMIP6) to update projections of future CAP. Models project that nearly the entire Northern Hemisphere exhibits increasing winter CAP with continued warming [by at least 5% (1°C) −1 global warming throughout, and over 30% in the Arctic and eastern Asia]. Summer CAP increases over the Pacific Ocean (2%–10%) and Arctic (up to 20%) but decreases over midlatitude continents and the Atlantic Ocean (exceeding 20% in places). These outcomes result from the relative balance between two overarching and often opposing trends: Extratropical cyclones (and therefore CAP events) become less frequent (except in the Arctic), but the average event produces more precipitation in the future (especially by more intense precipitation rates). Historically, CAP intensity trends are driven more by moisture availability than cyclone intensity (i.e., stronger winds); projections indicate future CAP intensity enhancement will be driven almost entirely by moisture availability. The strongest CAP trends historically are increases on the west side of the midlatitude oceanic storm tracks, but projections indicate that the Arctic Ocean will exhibit the strongest positive future trends because of exceptional increases in moisture availability combined with little change to storm frequency or intensity. Significance Statement Large storms called extratropical cyclones are responsible for most precipitation falling in the midlatitudes and the Arctic, especially in winter. We examined 18 state-of-the-art climate models to update projections of how precipitation associated with these storms is likely to change with continued global warming. Overall, two dominant trends were that there are fewer storms in the future and that typical storms produce more precipitation in the future than today. These trends counteract each other. In winter, the trend toward more intense precipitation wins out, so storm-associated precipitation increases nearly everywhere. Notably, increased precipitation intensity is not related to the strength of the storms. Instead, the increase occurs almost entirely because of greater evaporation as the world warms.