In the Puget Sound region of the Pacific Northwest, an atmospheric river (AR) event in 2022 caused extensive flooding across the region, especially around Seattle’s Duwamish River estuary. The event was characterized by concurrent astronomically large king tides, rain-on-snow river flooding, and storm surges, known as a “compound flood” event, yet the contributions from each mechanism were not well understood. Here, we elucidate the contribution of each flood driver to estuarine flooding during the event using a coupled atmosphere-hydrologic-ocean modeling framework. This framework couples regional atmospheric (SCREAM - Simple Cloud-Resolving Energy Exascale Earth System (E3SM) Atmosphere Model), hydrology (DHSVM – Distributed Hydrology Soil Vegetation Model), and coastal hydrodynamic (FVCOM – Finite-Volume Community Ocean Model) models. As validated against observed total water levels, the modeling framework accurately captured the tidal ranges and timing, as well as influence from storm surges and river discharge. Mechanistic analysis of tide, river, and surge effects on Duwamish region flooding reveals king tides as the leading contributor to flooding, followed by surge and river-enhanced water levels. River flooding is shown to have the most significant spatial gradient in impacts over the relatively short (~14 km) estuarine region. We used a pseudo global warming approach to project how this compound flood event may evolve under the impact of median-projection sea level rise (SLR) and climate change, and examined the changing role of tides, surge, and river flows in modulating the spatiotemporal patterns of flooding.