The most extreme precipitation events over the eastern United States from 1950 to 1996: Considerations of scale

The intensity or magnitude of a given heavy precipitation event is typicall y associated with the greatest point precipitation total. The scale or size of the heavy precipitation region, however, is important because it affect s the scale of the flooding potential (e.g., local- vs regional-scale basin s). In this study, a heavy-rain climatological description is constructed t hat identifies all precipitation events for the period of 1950-96 and estim ates the heaviest mean 2-day precipitation totals over a range of spatial s cales (i.e., circular regions from 2500 to 500 000 km(2)). Ranks of the mos t extreme precipitation events are provided for four regions of the study a rea for each of the 10 spatial scales. To develop the dataset, daily precip itation totals from the cooperative observer network are spatially interpol ated 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 regio ns displaying the greatest mean 2-day precipitation totals over each spatia l scale and 2) to link nearby regions of different scales together to form precipitation events. Precipitation events with regional recurrence interva ls of approximately 1 yr or greater at each spatial scale are examined and compared across four subregions. The geographical and seasonal distribution s of these events are provided. The extreme events are also tied to the occ urrence of tropical cyclones and 500-hPa cyclones. Secular trends are ident ified in the frequency of extreme events over the different spatial scales.