A drainage system’s performance reduces with time and degrades due to multiple factors. Street flooding and over-topping drainage systems were occurring in Merawi town. The objective of this study is to assess the performance of the drainage systems in Merawi town using the SWMM model. The SWMM model is one of the most popular models for urban flood planning and control. The digital map and pipeline network are used to set up SWMM work. The study employed both primary and secondary data collection. The sub-catchment characteristics and the storm sewer conduits are used to determine the parameters of the model. The simulated results indicate that the examined area would be flooded for 2, 5, 10, 25, 50, and 100-year return period precipitation. Hydrological and hydrodynamic modeling play a key role in the hydraulic, structural, and environmental impact assessment tasks in the urban drainage system. Climate change is one environmental threat that poses great challenges to the future development prospects of Merawi. The study used statistically downscaled daily data in 30-year intervals from the second generation of the Earth System Model (CanESM2) under two Representative Concentration Pathways (RCPs): RCP 4.5 and RCP 8.5 for two future time slices at 2040 and 2070. The projected annual minimum and maximum temperatures are expected to increase by 0.16°C, 0.99°C, 0.53°C, and 1.54°C in the 2040s and 2070s under the RCP4.5 scenario, respectively. Under RCP8.5, the annual minimum and maximum temperatures are expected to increase by 0.24°C, 1.72°C, 0.59°C, and 2.28°C in the 2040s and 2070s, respectively. Besides, the precipitation is expected to increase under intermediate and high emission scenarios by 0.236%, 0.681%, 0.846%, and 0.919% in the 2040s and 2070s, respectively. In both emission scenarios, the greatest changes in maximum temperature, and minimum temperature but non aristocratic changes in precipitation are predicted by the end of the century. According to the study, climate change would have been increased in the future, thus it should have brought an impact on the urban flood drainage system. Based on the research result we have recommended specific problems. Those are, LID to reduce runoff production. Continuous monitoring of the drainage facilities, proper dump site selection and solid waste management method is required. Keywords: stormwater drainage, SWMM, Runoff Generation, RCP scenario, LID