Assessing the performance of urban drainage systems under climate change impact

Abstract

This study evaluates the resilience and effectiveness of urban drainage systems in mitigating flood risks under current and future climate conditions, using Namasuba, a densely populated suburb of Kampala, Uganda, as a case study. Employing the PCSWMM hydrologic-hydraulic modelling platform, the study first simulated baseline drainage system performance under storm events of 10, 25, and 50-year return periods, utilizing historical rainfall data (1995-2024) analysed through Intensity-Duration-Frequency (IDF) curves generated using Gumbel distribution. To assess future impacts, precipitation projections were derived from the CMIP6 climate model (BCC-CSM2-MR) for two climate scenarios, SSP2-4.5 and SSP5-8.5. Bias correction of global model outputs to local conditions was achieved using Quantile Delta Mapping (QDM). Simulation results under future climate scenarios showed significant increases in runoff volume, flood duration, and the number of flooded nodes, with SSP5-8.5 presenting the most severe impacts. To address these impacts, Low Impact Development (LID) measures, specifically infiltration trenches and rain barrels, were implemented within the PCSWMM simulations. These adaptations demonstrated substantial effectiveness, significantly reducing flood volumes and durations. The findings underscore the vulnerability of existing urban drainage infrastructure in Namasuba to climate-induced flooding and highlight the importance of incorporating adaptive stormwater solutions into future urban planning strategies. This research contributes directly to achieving Sustainable Development Goals (SDGs) 11 (sustainable cities and communities) and 13 (climate action), providing actionable insights for policymakers and urban planners to enhance resilience and sustainability in urban areas.