Storm Precipitation Structure in the Eastern United States: Part I, Spatial Changes

A number of studies have examined the spatial patterns of either long term trends in precipitation totals or extreme precipitation event statistics. However, storm precipitation structures have rarely been analyzed for large spatial regions and/or long time periods. During a project to modernize climate inputs for estimating soil erosion rates in the eastern two-thirds of the U.S., a number of storm precipitation structure variables were derived from NCDC 15-minute gauge data (TD-3260). Storm duration, storm frequency, maximum 15- and 30-minute storm precipitation intensities, measures of the temporal distribution of precipitation within storms, and storm erosivity are some of the more prominent indicators of storm structure that have been generated. These storm structure indicators can reveal changes over space and time of precipitation origins (e.g., convective vs. stratiform events) and impacts (e.g., soil erosion rates) that are not discernable in commonly used approaches.

The purpose of this paper is to examine the spatial variance of storm structure in the eastern U.S. during the period since the 1970s, when the 15-minute precipitation data became more readily available in digital form. Spatial clustering of mean storm structure parameters at stations is used to regionalize storm structures by season. The spatiotemporal modes of storm structures in the climatological seasons will be presented, and variations from normal states to El Nino and La Nina will be described.