Proxy- and Model-Estimated Coupled Megadroughts in the Southwestern Regions of North and South America

The North American Southwest (NASW) and South American Southwest (SASW) are regions susceptible to prolonged and intense droughts that can span a decade or more (i.e., megadroughts). Although the drivers and impacts of megadroughts in each region and their co-occurrence have been examined in paleoclimate reconstructions, it is not known whether climate models simulate co-occurring megadroughts in these regions with characteristics and drivers that are similar to the real world. We compare the temporal characteristics of concurrent megadroughts and the Pacific Ocean conditions associated with these events in the Paleo Hydrodynamics Data Assimilation (PHYDA) product and the Community Earth System Model Last Millennium Ensemble (CESM-LME). We find that concurrent megadroughts in PHYDA and CESM-LME have similar temporal characteristics, but the relationship between hydroclimate conditions in the NASW and SASW is different between proxy-based estimates and the climate model. Further analyses reveal that changes in the tropical Pacific Ocean are weaker during concurrent megadroughts in the CESM-LME compared to those in PHYDA and that their teleconnection patterns and strengths are different. Reconstruction methodology is also found to be a factor in how the relationship between the tropical Pacific and each region is characterized. These results together indicate that while the CESM-LME simulates concurrent megadroughts with temporal characteristics similar to PHYDA, it does so for different reasons; this result leaves open the question of whether climate models used for future projections can accurately capture the risk of concurrent megadroughts in future projections.