Concurrent modes of climate variability linked to spatially compounding wind and precipitation extremes in the Northern Hemisphere

Compound wind and precipitation (CWP) extremes often cause severe impacts on human society and ecosystems, such as damage to crops and infrastructure. Spatially compounding events with multiple regions affected by CWP extremes in the same winter can impact the global economy and reinsurance industry; however, our understanding of these events is limited. While climate variability modes such as El Ni & ntilde;o Southern Oscillation (ENSO) can influence the frequency of precipitation and wind extremes, their individual and combined effects on spatial co-occurrences of CWP extremes across the Northern Hemisphere have not been systematically examined. Here, by combining reanalysis data and climate model simulations, we investigate how two oceanic and two atmospheric variability modes - ENSO, the Atlantic Multidecadal Variability (AMV), the North Atlantic Oscillation (NAO), and the Pacific North American (PNA) - amplify the wintertime (December-February) frequency of daily CWP extremes and associated spatial co-occurrences across the Northern Hemisphere. We find many hotspot regions where concurrent variability mode anomalies significantly amplify wintertime CWP extreme event frequencies compared to single variability modes. By examining the relationships between frequencies of wintertime CWP extremes across regions, we identify dependencies enabling extreme spatially compounding events, that is winters with many regions experiencing CWP extremes. While ENSO is the most influential variability mode for such extreme spatially compounding events, the occurrence of these events increases further when multiple modes of variability are in anomalous phases. In particular, combinations of modes increase both the number of regions and the population exposed to daily CWP extremes in the same winter. For example, combined ENSO- and NAO+ nearly doubles the number of affected regions compared to neutral conditions on average. Our analysis highlights the importance of considering the interplay between variability modes to improve risk management and adapt to the impacts of spatially compounding CWP extremes.