Characteristics of temporal pattern and return period of short-duration rainfall at Beijing Observatory

Using the rainfall autographic records with 1-minute interval at Beijing Observatory from 1961 to 2004, we have performed theclassification of short-duration rainfall pattern with fuzzy identification method and statistical analysis method. The Exponential distribution,Gumbel distribution and Pearson-Ⅲ distribution are also fitted to infer the short-duration rainfall extremes, such as 5-min, 10-min,15-min, 20-min, 30-min, 45-min, 60-min, 90-min, 120-min and 180-min extremes, based on the establishment of the probability distribution pattern under different return period scenarios, respectively. Results indicate that the amounts of rainfall mainly concentrate on 50-100 mm, but inter-decadal variations of torrential rain days are evident. The monthly temporal patterns are different so that the bimodal type is dominant in June while the unimodal type is mainly temporal pattern from July to September. The dominant temporal patterns of the short-duration rainfall process at Beijing Observatory are unimodal type, which account for more than 80% of all short-duration rainfall process. The maximum precipitation occurs in the two periods from afternoon to evening and before dawn. Pearson-Ⅲ distribution is an adequate fit to the probability distribution of the short-period precipitation probability at Beijing Observatory according to the comparison among the fittings of Exponential distribution, Gumbel distribution and Pearson-Ⅲ distribution. The maximum amount of precipitation under different return period increases with return period. That is the rainfall amounts of 10-min, 60-min and 180-min from 2 years to 100 years return period are limited in 10.4-22.6 mm, 22.3-59.2 mm and 53.0-89.8 mm, respectively. All these results will provide a more scientific support to prevent ur-ban waterlogging deposition and drainage system planning.