Widespread summer droughts across the contiguous UnitedStates (pan-CONUS droughts) pose unique challenges because of their potential to strain multiple water resources simultaneously and the significant financial damages that they impose. For example, pan-CONUS droughts in 1988 and 2012 cost an estimated $40 and $30 billion, respectively. Hun Baek, a graduate student in the PaleoDynamics Lab, has studied these droughts in detail, first using atmospheric model simulations to study the causes of these droughts over the last ~150 years. In a new paper, Hun has now provided a millennium-length perspective on the causes of pan-CONUS droughts and shown that the results from his paleoclimatic analysis agree well with his model findings that focused on the last century and a half. His principal finding is that La Niña events in the tropical Pacific are the principal oceanic influence on these droughts, while variability in the Atlantic has not played a significant role. These results are important for predictions of pan-CONUS droughts, and for determining how the occurrence of these droughts may change in the future due to increases in greenhouse gas emissions. An important methodological milestone of this study is the first application of the Paleo Hydrodynamics Data Assimilation (PHYDA) product for use in a paleodynamics context. The PHYDA was developed by Nathan Steiger as a postdoctoral scientist in the PaleoDynamics Lab. The abstract of Hun's paper is given below, while his paper can be found here.
Abstract: We examine oceanic drivers of widespread droughts over the contiguous US (herein pan‐CONUS droughts) during the Common Era in what is one of the first analyses of the new Paleo Hydrodynamics Data Assimilation product (PHYDA). The canonical understanding of oceanic influences on North American hydroclimate suggests that pan‐CONUS droughts are forced by a contemporaneous cold tropical Pacific Ocean and a warm tropical Atlantic Ocean. We test this hypothesis using the paleoclimate record. Composite analyses find a robust association between pan‐CONUS drought events and cold tropical Pacific conditions, but not with warm Atlantic conditions. Similarly, a self‐organizing map analysis shows that pan‐CONUS drought years are most commonly associated with a global sea surface temperature pattern displaying strong La Niña and cold AMO conditions. Our results confirm previous model‐based findings for the instrumental period and show that cold tropical Pacific Ocean conditions are the principal driver of pan‐CONUS droughts on annual timescales.