Changes in the Mechanisms Causing Rapid Drought Cessation in the Southeastern United States of America

Abstract

The synoptic processes that end droughts are poorly understood, yet have significant climatological implications. Here we examined the spatiotemporal patterns of rapid drought cessation (RDC) in the southeastern United States during the1979–2013 warm season (April–November) for three storm types: Frontal, Tropical, and Air mass. We defined RDC as a 1 month shift in soil moisture sufficient to alleviate an existing drought. We found that 73% of all warm-season droughts were ended by RDC events and the three storm-type groups ended droughts over similar spatial areas. Frontal storms were the most frequent mechanism for RDC events, yet their occurrences significantly decreased and were negatively related to increases in Northern Hemisphere air temperatures. Projected future warming in the Northern Hemisphere suggests a continued decline in the frequency and relative contribution of Frontal storms as RDC events, potentially influencing the timing and spatial scale of drought cessation in the southeastern U.S.