Record-Breaking Microstorm System Supports New Rainfall Frequency Estimates in Illinois

Abstract

An unusually severe microstorm system developed on 11 August 1993 in Champaign in east-central Illinois where continuous weather records have been maintained for 104 years. Total rainfall in the 1993 storm exceeded the previous 103-year maximum by nearly 50%. Analysis provides strong evidence that even a 100- year record of point rainfall may be misleading in estimating the frequency of extreme rainfall events for that point and the immediate vicinity. Mean frequency relations based on several stations in a region of homogeneous precipitation climate are more reliable predictors, as illustrated in the text. The problem of natural time and space variability in the distribution of extreme rain events is shown from analysis of the 104-year record.