Effect of climate change on the flooding of storm water networks under extreme rainfall events using SWMM simulations: a case study

Urban areas are becoming more susceptible to severe storms, flash floods, and drainage system failures due to climate change, population growth, and urbanization. Flood modeling is a useful method for managing storm water drainage networks, predicting behavior, and evaluating effective solutions to structural and operational problems. This research describes the application of the Stormwater Management Model (SWMM) to evaluate the performance and effectiveness of the rainwater network, identify flood-prone locations, and determine the extent of floods in the center of Kerbala Governorate, Iraq. Saif Saad neighborhood was chosen as a case study. The model's validity was confirmed using the occurrence of actual rainfall by the coefficient of determination (R² = 0.8952), normalized mean square error (NMSE = 0.0964), and Nash–Sutcliffe efficiency (NSE = 0.7152), and the model's performance was reasonably good. Simulation results indicated that the system works well under near-term rainfall events, except for some sites that require maintenance and the diversion of surplus water to nearby green spaces. Over time, in periods of medium and far future until the year 2100, the system showed an increase in manhole floods, exceeding 0.1 m³/s. The percentage of flooding in manholes was more than 13% in the worst case, and continued floods for longer periods could potentially negatively affect the current drainage infrastructure. The study provides technical support for decision-makers to address these issues. By providing a comprehensive view of flood-prone areas and sites, as well as the flood percentage for each under different climate change scenarios, with the help of the Geographic Information System (GIS) software to represent future rain events. It suggests increasing the depth of manholes most vulnerable (especially R18, R98, and R101A manholes) to flooding and correcting slopes to achieve sustainability and a good service rate for the storm drainage system.