B.S.T.J. Briefs: A Simple Method for Estimating Five-Minute Point Rain-Rate Distributions Based on Available Climatological Data

A Simple Method for Estimating Five-Minute Point Rain-Rate Distributions Based on Available Climatological Data By W. Y. S. CHEN (Manuscript received August 27, 1975) This brief presents a method for estimating 5-minute rain-rate distributions based on climatological data for over 250 locations as published annually by the National Oceanic and Atmospheric Administration (NOAA). A maximized 5-minute rain-rate distribution, which is believed to be more appropriate for use in predicting rain attenuation, is also introduced. The sample form in Table I, showing the N O A A method of computation of maximum short-time rates of rainfall for the years 1896-1935, is taken from Ref. 1. On this form are shown the storms of July 14, 1912, and September 2, 1922, at Washington, D. C. The times of beginning and ending of the storms and other data are entered on the "Obs. Precip." line, which shows the precipitation at consecutive 5-minute intervals up to 50 minutes from the beginning of the period of excessive precipitation, as copied from Weather Bureau records. The "Increment" entries are computed directly from the figures on the line above. The maximum precipitation shown for any storm is the maximum for the time period indicated by the figure in the column heading, and is determined by selection from the 5-minute increments. For example, in the 1912 storm, the maximum precipitation indicated for 5 minutes occurs in the sixth increment, that for 10 minutes is found by combining the fifth and sixth increments, and that for 20 minutes is found by combining the fourth, fifth, sixth, and seventh increments.