Calculation method of short-duration rainstorm intensity formula considering nonstationarity of rainfall series: impacts on the simulation of urban drainage system

The changing nature of the Earth's climate and rapid urbanization lead to the change of rainfall characteristics in urban areas, the stability of rainfall series is destroyed and it is a difficult challenge to consider this change in urban drainage simulation. A generalized additive model (GAMLSS) with time as covariant was established to calculate and predict the design values of extreme rainstorm return period, and the nonstationary short-duration rainstorm intensity formula of three periods was fitted and compared with the stationary formula. The urban water simulation model and the MIKE 21 two-dimensional surface flow model are coupled to simulate the urban flood under different formulas and different return periods. The results show that the nonstationary results are worse in the same period. In the 5-year return period rainfall–runoff simulation performance, the nonstationary inundation area is 18.5% more than the stationary, and inundation water is 23.5% more than the stationary. The nonstationary simulation results show higher inundation depth and slower flood recession process. These gaps will widen in the future, but they will become less significant as the return period increases. It can provide a reference for the study of flood control work and the design of existing drainage infrastructure in the region.