Impacts to San Francisco’s Combined Sewer System from Climate Change Induced Stressors

San Francisco is the only coastal city in California, and one of the few on the West Coast of the United States of America, that uses a combined sewer system managing both wastewater and stormwater in a single conveyance system. During heavy rainfall, the system can be overwhelmed, leading to untreated discharges from 43 outfall points into San Francisco Bay. This research develops a comprehensive numerical model using PCSWMM to simulate San Francisco's storm and sewer infrastructure, including transport/storage tunnels and pump stations, assessing the impacts of intensified rainfall on drainage performance. Using geographic information systems data and climate change projections, this study estimates increased flow volumes and the frequency of combined sewer overflows. Results pinpoint areas most susceptible to untreated discharges, providing critical insights for enhancing urban drainage resilience against future climate change impacts.