The Most Extreme Precipitation Events over the Eastern United States from 1950 to 1996: Considerations of Scale

Abstract

The intensity or magnitude of a given heavy precipitation event is typically associated with the greatest point precipitation total. The scale or size of the heavy precipitation region, however, is important because it affects the scale of the flooding potential (e.g., local- vs regional-scale basins). In this study, a heavy-rain climatological description is constructed that identifies all precipitation events for the period of 1950?96 and estimates the heaviest mean 2-day precipitation totals over a range of spatial scales (i.e., circular regions from 2500 to 500 000 km2). Ranks of the most extreme precipitation events are provided for four regions of the study area for each of the 10 spatial scales. To develop the dataset, daily precipitation totals from the cooperative observer network are spatially interpolated onto a finescale (10 km by 10 km) grid over the eastern two-thirds of the United States. An automated algorithm is developed 1) to identify regions displaying the greatest mean 2-day precipitation totals over each spatial scale and 2) to link nearby regions of different scales together to form precipitation events. Precipitation events with regional recurrence intervals of approximately 1 yr or greater at each spatial scale are examined and compared across four subregions. The geographical and seasonal distributions of these events are provided. The extreme events are also tied to the occurrence of tropical cyclones and 500-hPa cyclones. Secular trends are identified in the frequency of extreme events over the different spatial scales.