This study uses agent-based modelling (ABM) to assess the socio-hydrological impacts of structural coastal flood protections (SCFPs) under different climate change scenarios considering three contrasting UK case studies: Southport, Weston-super-Mare, and Portsmouth. By integrating extreme coastal water level (ECWL) projections and population dynamics, the ABM simulations reveal five distinct phases: Design, Implementation, Latency, Flood, and Post-Flood. The results highlight that the Latency phase, whereby SCFP initially stabilises affected population (AfP), inadvertently encourages population growth in residual risk areas. This process exacerbates long-term flood exposure, leading to significant increases in AfP when ECWL exceeds the SCFP crest height, negating gains in flood protection from the initial construction/upgrade. As such, Southport and Weston-super-Mare saw a significant increase in coastal population within protected floodplains, with these populations potentially having limited experience with flooding, preparedness, and consequently heightened vulnerability. Conversely, Portsmouth, with limited residential development near SCFPs, demonstrated how existing land-use and high population density can reduce the unintended socio-hydrological consequences of SCFPs in densely-populated coastal settings. These findings reveal two key pathways that influence coastal population in response to SCFPs: Land-use Driven, where non-residential land-use limits population increase, and Population Driven, where high-density areas limit further growth. This study advances our understanding of the coupled human-flood dynamics by evaluating how SCFPs can increase flood impacts in the long-term by influencing socio-spatial distribution over the short- to medium-term. Moreover, it demonstrates how ABMs can provide valuable insights by simulating complex coupled human-flood dynamics; critical for supporting adaptive, resilient coastal management strategies in a changing climate.This research was funded by the EPSRC grant number EP/T518116/1
