Rain-rate distributions and extreme-value statistics

An extension of a method of Chen and Lahlum1 for estimating the distributions of high rain rates is described. Through application of the statistical theory of extremes to available yearly maximum rain-rate data, a reasonably accurate distribution is obtained. The calculated results agree well with previously obtained 20-year data. Application of this method to Weather Bureau Rainfall Intensity-Duration-Frequency Curves has yielded 50-year distributions of 5-minute rain rates for 36 locations in the western United States; others can be similarly obtained. Such long-term rain-rate distributions are valuable for microwave radio-path engineering, especially in the western United States where shorter-term data sources are inadequate.