Abstract:

Saltwater intrusion in the Changjiang River Estuary is generally considered a key threat to urban water supply security, and the risks may be exacerbated under the weather conditions of concurrent typhoons and low river discharge. Taking the successive landfalls of typhoons “Bebinca” and “Pulasan” along the north bank of Hangzhou Bay, Shanghai, in September 2024, as examples, we employed a high-resolution 3D estuarine saltwater intrusion numerical model to simulate the differential impacts of the typhoons on saltwater intrusion in the Changjiang River Estuary. The results indicated that whereas the onshore wind-driven circulation promoted a significant enhancement of the frontal intrusion upstream of saltwater in the North Channel during the landfall of typhoon “Bebinca,” the circulation weakened the saltwater intrusion in the South Passage. In contrast, given its less intense strength and deflected track, typhoon “Pulasan” had a comparatively limited impact on the frontal intrusion in the North Channel. Given their limited duration, the short-term storm surges induced by the typhoons, which coincided with spring tides, caused comparatively little saltwater spillover from the North Branch into the South Branch. The findings of this study reveal the response mechanisms of saltwater intrusion to the landfall of typhoons on the north bank of Hangzhou Bay. This will provide a scientific basis for defense against compound natural disasters involving the combined effects of typhoons and saltwater intrusion on urban water supplies under extreme climate conditions.

Key words: the Changjiang River Estuary, saltwater intrusion, landfalling typhoons, wind-driven circulation, numerical simulation