Drought in the U.S. Southeast, Model Bias, and Climate Change

One of the consequences of global warming will be changes in drought and flood cycles, with both projected to become more extreme. In the U.S. Southeast drought is correlated with large-scale dynamical features such as the El Nino/La Nina cycle and the Bermuda High. This study focuses on the role of the Bermuda High in the flux of moisture into the continental U.S. during June. It is primarily a model study, investigating three resolutions of the Community Atmosphere Model (CAM, V3.6) and the Modern Era Retrospective-Analysis for Research and Applications (MERRA). The model shows a strong propensity for excessive drought in the U.S. Southeast, with the moisture flux and precipitation strongly correlated. There is only minor improvement with the increase of resolution. We investigate the correlation of this drought with bias in the representation of the Bermuda High. In the MERRA Re-analysis we show that this drought is “corrected” by the insertion of moisture data in the boundary layer. We discuss the mechanisms responsible for the transport of water, and the implications for interpretation of regional drought in the U.S. Southeast in climate change projections.