Estimating Probable Maximum Precipitation - From Research to Design

There are two widely used methods for estimating Probable Maximum Precipitation (PMP), namely, the hydro-meteorological and statistical techniques which are characteristic of the deterministic and probabilistic approaches respectively. International research shows substantial differences in the results obtained by these methods. The present study uses data from several agro-ecological regions of Sri Lanka to estimate 24-hour point PMP. The statistical method is applied in three different ways; with equal sample size, increasing sample size and a continuous data set. Results show that the differences are less than 10%, thus demonstrating consistency and dependability of the method. When compared with the hydrometeorological method, both approaches yield results which are in close agreement at several stations. The wind and moisture maximization factors play a crucial part in the hydrometeorological procedure. Also considering the ease of analysis, the study strongly suggests the statistical method as efficient and appropriate for estimating PMP in design office practice and for developing PMP maps for Sri Lanka. Aspects needing further investigation are also mentioned.