Estimating the impacts of recurrent and expanding coastal flooding on septic systems in Maryland's Chesapeake Bay.

Projected sea-level rise (SLR) is expected to substantially expand coastal flood extents across Maryland's Chesapeake Bay, with implications for decentralized wastewater infrastructure. This study integrates modeled coastal flooding scenarios from 2020 to 2060 with septic systems locations to quantify exposure under daily and annual flood conditions and identify areas where exposure intersects with high social vulnerability. Findings highlight spatial heterogeneity in flood impacts, with Dorchester County experiencing the largest flood extent and Worcester the steepest proportional increase in both flood extent and septic system exposure. By 2060, flood extent is projected to increase by 44% in Wicomico and exceed 260 km² in Somerset. Across the region, the number of affected septic systems more than doubles, with Worcester exhibiting a sevenfold increase from baseline and Dorchester surpassing 1,700 systems exposed. Flood frequency is also projected to increase, with hundreds of systems transitioning into monthly or weekly inundation by 2060, particularly in Dorchester and Somerset counties. Spatial aggregation identifies clusters of septic system exposure across the region. The spatial configuration of flood-exposed systems and social vulnerability varies across block groups, indicating that increasing flood exposure and recurrence affect communities with differing demographic characteristics. Supplementary Information: The online version contains supplementary material available at 10.1007/s10584-026-04172-x.