Rain-Rate Distributions and Extreme-Value Statistics

References 2 and 3 describe a procedure for obtaining long-term (^ 20 years) distributions of 5-minute rain rates from data published by the National Climatic Center. 4 Such distributions have been obtained for 202 locations in the eastern and midwestern United States and applied to path engineering of 11-GHz radio links. However, the excessive short duration rainfall data 4 on which these distributions are based contain only rainfalls that exceed an excessive rainfall threshold defined by the National Climatic Center. 2,3 For example, the threshold is 75 mm/hr for 5-minute intervals. In low rain-rate areas, such as Oregon and Washington, almost all rainfalls do not exceed the threshold and, hence, are not included in the excessive short-duration rainfall data. For example, at Spokane, Washington, the 5-minute rain rate exceeded the 75 mm/hr threshold only once in the 20-year period from 1953 to 1972. This data source, therefore, is an unsatisfactory basis for radio-path engineering in such areas. On the other hand, processing other longer-term data--say 50 years--is tedious and costly. This has motivated the search for an alternative method. Fortunately, the statistical behavior of the extremes of a 1111