Study on Urban Rainstorms Design Based on Multivariate Secondary Return Period

With the rapid urbanization, waterlogging losses caused by rainstorm are becoming increasingly severe. In order to reveal the correlations between rainstorm characteristic elements, and make the calculation of rainstorm return period more reasonable and objective, this study established the joint distribution models of rainstorm elements by using copula theory based on the rainfall data in a Chinese megacity, Zhengzhou. Then their combined design values of primary return period (PRP) and secondary return period (SRP) are derived by the maximum probability method and the same frequency method. Finally, the rainstorm pattern was acquired associated with Pilgrim & Cordery method (PC). The results indicate that the calculation of rainstorm return period (RRP) with SRP is more reasonable than PRP. For same RRP, the rainstorm volume (RV) of “Or” return period type is largest, while the “And” return period’s is smallest, and the RVs of Kendall return period and survival Kendall return period are between them. Concerning Kendall return period, the RVs calculated by the maximum probability method and the same frequency method are pretty close, and their relative deviations are from -5.84% to 4.69%. Compared to “Or” return period, the rainstorm patterns of Kendall return period can reduce the magnitude and investment of the stormwater infrastructure. Moreover, the rainfall with designed rainstorm pattern of survival Kendall return period mainly concentrated before the rain peak in contrast with Kendall return period.