Calculation and Comparison Analysis of Rainstorm Intensity Formulas in Dazhou

Two rain intensity formulas are derived by different sampling methods，annual maximum value and annual multi－sampling method，based on 53 years rain data from 1961 to 2013; during the derivation process two steps are used to get the coefficients．Firstly，we employ three frequency distribution curves to fit the sample data and get the i-t-p table; secondly，least square method and Guass-Newton method are applied to derive relative coefficients on the basis of these tables．Results from comparison of this two equations show that the rainstorm intensity of annual maximum value method is higher that that of annual multi-sampling method in low return period．However when precipitation time is long，the rainstorm intensity of annual multi-sampling is much higher．