Co-occurrence of California Drought and Northeast Pacific Marine Heatwaves Under Climate Change

Motivated by the uncommon yet highly impactful co-occurrence of California (CA) drought and a northeast Pacific (NEP) marine heatwave (MHW) during 2013-2016, we examined such compound extremes in Coupled Model Intercomparison Project Phase 6 projections, comparing the end of the 21st century with the preindustrial period, and separating effects of long-term trends from interannual variability. Here, we show that long-term trends due to anthropogenic climate change will dramatically increase the co-occurrence of extreme dry CA and warm NEP conditions. When trends are removed, the co-occurrence of CA drought and Gulf of Alaska (GOA) MHW will increase while the co-occurrence of CA drought and California Current (CC) MHW remains unchanged. A stronger link between GOA MHW and subsequent CC MHW as well as decreased persistence in CA drought are also projected under anthropogenic warming. These frequency changes are consistent with shifts in distributions of sea surface temperature and soil moisture anomalies associated with individual extremes.