Estimation of Probable Maximum Precipitation Using Statistical Methods

N. Vivekanandan

Probable Maximum Precipitation (PMP) is generally used to arrive at estimates for Probable Maximum Flood (PMF) for planning, design and risk assessment of high hazard hydrological structures. PMP represents the greatest depth of precipitation for a given duration which is physically possible over a given size storm area at a particular geographical location and at a particular time of year. Statistical method, empirical method and dynamic method is generally available for estimation of PMP for non-orographic or plain area regions. In this paper, statistical method is used for estimation of PMP. Extreme Value Type-1 distribution (EV1) is adopted to estimate the extreme rainfall and the results are compared with the 1-day PMP obtained from Hershfield method. Anderson-Darling test is applied for checking the adequacy of fitting of EV1 distribution to the series of annual 1-day maximum rainfall data. Wald-Wolfowitz run test and Mann-Whitney Wilcoxon U-test is performed on the rainfall data to check the randomness and homogeneity of the data series. Grubbs test is applied to identify the outliers in the data series. The study suggests the estimated 1-day PMP viz., 25.7 cm for Devarapalle and 46.3 cm for Visakhapatnam could be used to arrive at PMF estimates for design purposes.