TY - JOUR T1 - Increasing magnitudes and frequencies of extreme precipitation events used for hydraulic analysis in the Midwest JF - Journal of Soil and Water Conservation SP - 179 LP - 184 VL - 61 IS - 4 AU - C.E. Davis Todd AU - J.M. Harbor AU - B. Tyner Y1 - 2006/07/01 UR - http://www.jswconline.org/content/61/4/179.abstract N2 - Precipitation depths for high magnitude, low frequency storm events are critical inputs in designing hydraulic and erosion control structures for soil and water conservation. The common standard for precipitation magnitude and frequency data prior to 2004 was National Weather Bureau Technical Paper 40, which has been superseded by National Oceanic and Atmospheric Administration (NOAA) Atlas 14. Comparison between these two reports for Midwestern sites with long climate records reveals important changes in design storm events; in some cases event magnitudes increased up to 46 percent. The 24-hour 100-year recurrence interval precipitation depth increased at 89 percent of study locations, but there was little change in events with 2- and 10-year recurrence intervals. These changes most likely result from increased accuracy in precipitation statistics and localized patterns of increased storm magnitude. Because of the impact of these changes on the design of hydraulic and erosion control structures, design manuals and local ordinances should be updated to reflect the new data. ER -