Large Scale Influences on Drought and Extreme Precipitation Events in the United States

Abstract:

Observations indicate that extreme weather events are increasing and it is likely that this trend will continue through the 21^st century. However, there is uncertainty and disagreement in recent literature regarding the mechanisms by which extreme temperature and precipitation events are increasing, including the suggestion that enhanced Arctic warming has resulted in an increase in blocking events and a more meridional flow. A steady gradual increase in heavy precipitation events has been observed in the Midwestern and Northeastern United States, while the Southwestern United States, particularly California, has experienced suppressed precipitation and an increase in consecutive dry days over the past few years. The frequency, intensity, and duration of heavy precipitation events in the Midwestern United States and Northeastern United States, as well as drought in the Southwestern United States are examined using the Modern Era Retrospective Analysis for Research and Applications Version-2 (MERRA-2). Indices developed by the Expert Team on Climate Change Detection and Indices representing drought and heavy precipitation events have been calculated using the MERRA-2 dataset for the period of 1980 through 2014. Trends in these indices are analyzed and the indices are compared to large scale circulations and climate modes using a composite and statistical linkages approach. Statistically significant correlations are present in the summer months between heavy precipitation events and meridional flow despite the lack of enhanced Arctic warming, contradicting the suggested mechanisms. Weaker, though still significant, correlations are observed in the winter months when the Arctic is warming more rapidly than the Midlatitudes.