Interannual Variabilities of the Summer and Winter Extreme Daily Precipitation in the Southeastern United States

Abstract This study focuses on investigating how climate variabilities exhibited in summer and winter precipitation in the Southern United States (SEUS) are possibly modulated by large scale atmospheric activities, including El Nino-Southern Oscillation (ENSO) and cyclonic activities measured in Accumulated Cyclone Energy (ACE) Index. A stringent criterion was applied to the Global Historical Climate Network (GHCN)-Daily dataset to identify a total of 99gauge stations in the SEUS where data length is at least 60 years. Seasonal precipitation is normalized by annual total precipitation amount to obtain the season ratio. Two approaches, including the block maximum and peaks-over-threshold methods, were used to develop time series of extreme precipitations in the summer (June-October) and winter (December-February) seasons. Generalized Extreme Value (GEV) distribution was used to fit a probability density function to the 1-day maximum precipitation time series. Daily cumulative anomaly curves were developed to investigate potential changes in the onset and demise of rainy seasons for the region to the south of 30-degree latitude. Analyses found that summer ratios are over 55% for most stations in Florida and in the range of 45%-55% for most stations along the east coast. Summer total precipitation is significantly correlated with ACE for only 17.2% of the stations, while winter total is significantly correlated with Nino 3.4 for 46.5% of the stations. Similarly, the effect of ACE on the frequency and amount of extreme daily precipitation over the 95th threshold in the summer season is less strong compared to the effect of ENSO on winter extreme precipitation. Summer extreme precipitation is found to be modulated by geographic terrain as well as by local atmospheric activities. Analyses of the onset and demise of rainy season in Florida found no trend in the onset or demise dates between the years 1932 and 2003, although substantial interannual variability was observed.