Relationships between ENSO and drought over the southeastern United States

Abstract

A long term precipitation (P) data set over the United States and the sea surface temperature (SST) data from 1915 to 2006 were used to examine the impact of El Nino Southern Oscillation (ENSO) on drought and persistent wet spells over the southeastern United States. The meteorological droughts and wet spells were identified based on the 6‐month standardized precipitation index (SPI 6) calculated from P averaged over the Southeast. These events indicate that a drought (or wet spell) over the Southeast is more likely to start during a cold (warm) ENSO winter or early spring. The influence of ENSO on P is seasonally dependent. The P composites for cold ENSO events show positive P anomalies over the Southeast in winter but negative anomalies in summer. For warm ENSO events, the situation reverses. Therefore, a persistent cold (warm) ENSO from winter to summer does not create favorable conditions for drought (wet spells) to persist over the Southeast. While cold ENSO events are more likely to initiate droughts, droughts are likely to persist if the cold (warm) ENSO winter is followed by an ENSO neutral summer.