ENSO Impacts on heavy rain events in the Southeast

This study addresses variations of local risk of heavy rainfall events in the Southeast as related to ENSO phase. It provides information regarding climatological expectations during a particular ENSO phase. A heavy rainfall event is defined as two or more inches of rain observed within a two-day period. A two-day period is chosen because most heavy rainfall events begin and end within this period. Further, warm, cold and neutral ENSO phases are defined via the rank of the Multivariate ENSO Index (MEI) during the period 1950-2009. Occurrences of two or more inches of rainfall within a two-day period were tabulated for each month and ENSO phase during 1950-2009. Event occurrences are considered as Poisson variables. Relative risk of a heavy rainfall event is then expressed via Poisson exceedance probabilities of the number of occurrences of heavy rainfall events. Such probabilities are calculated for each month and ENSO phase at stations throughout the states of Alabama, Florida, Georgia, North Carolina and South Carolina. The probability of more/fewer events is valuable to water managers and irrigation planners. Also, results of this study address the field-scale variability of rainfall that is important in crop modeling. Contact Information JAMES J. O'BRIEN, Center for Ocean Atmospheric Prediction Studies, Florida State University, 2035 E. Paul Dirac Dr., Tallahassee,Florida 32306-2840, USA, Phone: 850-459-1938, Email: jim.obrien@coaps.fsu.edu