Extreme Rainfall Events in the Southeast: Spatial and Temporal Variations

The 2014 National Climate Assessment (NCA) states that the amount of heavy rain (99th percentile) has increased across many regions in the continental United States. In the Southeast US (SEUS), the amount of precipitation in these heavy rain events increased by roughly 27% based on data from 1958-2012. This study explored the spatial and temporal patterns of the heaviest rain events (90th, 95th and 99th percentiles) to determine how these events varied across the region and season. The data set utilized was the period of record daily data from the 270 Global Historical Climate Network (GHCN) stations in the Southeast. All stations used in the analysis met a standard of having less than 10% missing daily data. The poster focuses on three stations in different sub-regions of the Southeast as a way of assessing differences in seasonal and temporal patterns of heavy rain events. The analysis shows that spatially, coastal areas along the Gulf of Mexico and the Atlantic Ocean see a higher percentage of their annual rainfall from rare (99%) events than further north or inland, most likely due to the influence of tropical systems and proximity to the moisture source. Differences in the seasonal dominance of winter mid-latitude systems may also be a factor. Temporally, high percentile rainfalls contribute the most to seasonal precipitation in fall at the northern stations, where the average rainfall is the lowest of any season, and in winter at the most southern station studied. However, there is considerable year-to-year variability, which may reflect the influences of El Nino Southern Oscillation (ENSO) as well as other internal oscillations. Future work will focus on evaluation of trends in high-percentile rainfall as well as determining the relative importance of tropical versus mid-latitude influences and the impacts of antecedent rain on high-percentile events.