Atmospheric dynamics drive most interannual U.S. droughts over the last millennium

Area of Science:

• Paleoclimatology
• Climate Dynamics
• Atmospheric Science

Background:

• The American West faces increasing drought sensitivity due to growing populations.
• Historical paleoclimate data indicates severe pre-settlement droughts, impacting water management.
• Understanding past drought dynamics is crucial for future climate planning.

Purpose of the Study:

• To reconstruct past climate states using paleoclimate data assimilation.
• To conduct a large-scale multivariate investigation of U.S. drought dynamics over the last millennium.
• To identify key drivers of interannual drought variability.

Main Methods:

• Paleoclimate data assimilation for climate reconstruction.
• Multivariate statistical analysis of drought dynamics.
• Analysis of Community Earth System Model Last Millennium Ensemble simulations.

Main Results:

• La Niña conditions significantly influence Southwest U.S. drought but explain only ~13% of interannual variability.
• Atlantic sea surface temperatures show a minor influence on U.S. drought.
• A substantial portion of drought variability remains unexplained, suggesting internal atmospheric processes.

Conclusions:

• Internal atmospheric variability is a major factor in U.S. drought dynamics.
• While greenhouse gases will impact future drought risk, interannual variations will also be driven by internal atmospheric processes.
• Future drought risk assessment requires consideration of both external forcings and internal climate variability.