Climate change leads to the increase of frequency and intensity for extreme precipitation events, potentially threatening the development of our society. It is of great significance to study the spatiotemporal variation of precipitation for understanding cycle process of water and its response to global warming. This paper selects the Xijiang River basin, which locates on a low latitude and coastland, as the research area. The spatiotemporal distribution and homogeneity of precipitation are analyzed, and the spatial trend is studied using 12 extreme precipitation indices. Finally, chaotic characteristics are evaluated for daily precipitation. The results showed that the precipitation in the basin tended to be unevenly distributed. On wet days, precipitation in the middle and the west was more and more uniform. The proportion of tiny rain was the largest, between 33.5% and 41.3%. The proportion of violent rain was the smallest, between 0.1% and 4.7%. Duan had the highest frequency for violent rain, and the probability of disasters caused by extreme precipitation near the station was the highest. The simple daily intensity index (SDII) showed a significant increase in the middle and the northeast. PRCPTOT (annual total wet-day precipitation) showed a decreasing trend in the northwest. The average rates of variation for R95PTOT (precipitation on very wet days) and R99PTOT (precipitation on extremely wet days) were −0.01 mm/year and 0.06 mm/year, respectively. There might be a risk of drought on the west of the basin in the future. Precipitation in other locations was still relatively abundant. Daily precipitation showed high dimension and high chaotic characteristics. The MED (minimum embedding dimension) was between 11 and 30, and the MLE (largest Lyapunov exponent) was between 0.037 and 0.144.

Urban stormwater drainage networks in old urban districts often suffer from insufficient drainage capacity, adverse pipe slopes, and outdated design standards, which increase the risk of urban waterlogging during heavy rainfall events. To address these issues, this study proposes a multi-objective hydraulic optimization framework for the rehabilitation of urban stormwater drainage networks by coupling SWMM hydrodynamic simulation, an improved bottleneck index method, and the NSGA-III algorithm. The proposed bottleneck index integrates the ratio of actual hydraulic gradient to pipe slope with pipe filling ratio (h/D), enabling the identification of pipes with insufficient drainage capacity and unreasonable construction conditions. The Sanjie River catchment in Fuzhou, China, was selected as the study area. The results indicated that the maximum proportion of bottleneck pipes increased from 33.28% to 41.62% as the design storm return period increased from 1 to 30 years, while the rate of increase gradually diminished under larger return periods. Multi-objective optimization results showed that increasing the maximum allowable rehabilitated pipe diameter from 1.2 m to 1.5 m yielded only limited additional improvement in drainage performance, ranging from 2.06% to 4.11%, whereas the rehabilitation cost increased by 3.10% to 4.41%. Therefore, 1.2 m was identified as the more cost-effective maximum allowable diameter. Under this condition, the rehabilitation schemes for the 3-, 5-, 10-, and 20-year design storms reduced nodal overflow volume by 36.56%, 33.67%, 31.24%, and 27.24%, respectively. The proposed framework provides a systematic and practical approach for diagnosing and rehabilitating existing urban stormwater drainage networks.