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

Abstract. Compound wind and precipitation (CWP) extremes often cause severe impacts on human society and ecosystems, such as damage to agricultural crops and infrastructure. High regional frequencies of CWP extremes across multiple regions in the same winter, referred to as spatially compounding events, can further impact the global economy and the reinsurance industry. By combining reanalysis data and climate model simulations, we investigate the influence of two oceanic and two atmospheric variability modes – El Niño Southern Oscillation (ENSO), the Atlantic Multidecadal Variability, the North Atlantic Oscillation (NAO) and the Pacific North American (PNA) – on the frequency of wintertime CWP extremes and associated spatial co-occurrences across the Northern Hemisphere. In many hotspot regions, concurrent variability mode anomalies significantly amplify CWP extreme event frequencies compared to single variability modes. By examining the relationships between CWP extremes across regions, we identify dependencies enabling extreme spatially compounding events with many regions experiencing CWP extremes in the same winter. While ENSO is the most influential variability mode for such extreme spatially compounding events, combinations of modes are essential for the occurrence of these events across the Northern Hemisphere. In particular, combinations of modes amplify both the number of regions and population exposed to CWP extremes in the same winter, for example, they nearly double 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 mitigation of spatially compounding CWP extremes.