Storm-induced saltwater intrusion responds divergently to sea level rise in a complicated estuary

Global warming and sea level rise (SLR) not only increase the intensity and frequency of coastal hazards but also complicate associated dynamics. The exacerbated saltwater intrusion in this context will further be adversely affected by storms with deepening distances and growing duration, aside from the simultaneous coastal flooding they cause. Here, we investigate storm-induced saltwater intrusion and its responses to SLR in the Pearl River Estuary by numerical simulation. Predominant in competition with river runoffs, typhoons passing by cause fast stratification and dramatic increase of saltwater intrusion lengths via wind mixing. Stronger destratification and longer recovery time are linked to a narrow long channel, where the tidal excursion is weak owing to bay/channel-shape modulation. The rising sea levels enhance the tidal prism and shift the saline water universally to the upper reaches, and this impact tends to be amplified in the upper part of the bays owing to the narrowing bay shape and shoaling bathymetry. The saltwater intrusion length could be expressed as a linear relationship with the water level, but with divergent responses to storms, depending on bay/channel shapes. Amplification of saline intrusion is indicated in the channel-shaped estuary, but the farthest distance during a storm is less sensitive to SLR than in a bell-shaped estuary. The present study reveals the potential importance of storm-induced compound hazards to coastal communities, and highlights the notably specific salinity responses whereby tributary morphology.