The unreasonable assumption that the rainfall return period is similar to the runoff return period may lead to unreasonable drainage system design. Hence, this study proposes a computational framework to calculate the rainfall return period according to the runoff return period. Based on the Akaike Information Criterion (AIC) and the optimal probability distribution functions, a novel approach was proposed to combine the rainfall and maximum pipe flow return periods. Copula functions were employed to construct a joint probability distribution for calculating the rainfall return period using the maximum pipe flow return period. Thus, this study reached the following results. (I) The Gamma, Logistic, and Weibull distributions provided better descriptions for the rainfall and maximum pipe flow probability distributions. The Gaussian, Gumbel, and Survival Clayton Copula functions were shown to be the optimal choices. (II) A calculation method for the rainfall return period was constructed based on the Satisfaction Percentage (SP). For instance, using a 2-year as the maximum pipe flow return period, the rainfall return period was determined to be 4.705 years (60 min of rainfall duration, Maluan community) with an SP value of 0.95. (III) The study area showed non-significant impacts (p < 0.05) in selecting the rainfall return periods. Therefore, simulations can be conducted in regions with missing pipe network data using similar underlying surface conditions from other study areas.