When the failure of a hydraulic work involves a high risk of human losses and/or catastrophic material damages, its hydrological sizing is done with the probable maximum flood (PMF). The PMF is estimated based on the probable maximum precipitation (PMP), which takes into account the upper physically possible limit than can occur with certain duration within a basin of a particular geographic region. Hershfield statistical method and Koutsoyiannis probabilistic method are the simplest procedures to estimate the PMP; however, being based on the maximum observed precipitation data, their results are approximate and recommended exclusively for preliminary studies. In this study the above mentioned methods were applied to the 100 series of annual maximum daily precipitation (MDP) of over 40 values, available in the state of San Luis Potosi, Mexico. Statistical quality tests of these 100 records showed that nine records have persistence and three have a significant linear trend; therefore, they were corrected. Based on the Log-Pearson Type III and General Extreme Values distributions, a MDP prediction of the 10000 years return period was obtained, designated P-Tr. Two ratios were evaluated: PMP/Po and PMP/P-Tr, being Po the maximum observed value of MDP in the record. Their representative values are 3.50 and 1.45, respectively, which allow making quick estimations of PMP in 24 hours. The availability of estimated PMP in 24 hours of 100 locations in the state of San Luis Potosi allow further estimations such as weighted transport of nearby values; whereas in basins under study, the techniques of isohyets or Thiessen polygons can be used. As a conclusion, it is recommended to carry out this study and/or its updates in other states or regions of Mexico.
