Changing flood risks in estuaries due to global climate change: forecasts from observations, theory and models

Rising sea levels and enhanced storminess, resulting from Global Climate Change, pose major threats to the viability of estuaries worldwide. While numerical models can accurately simulate changes in estuarine responses for tides and surges, they cannot reliably predict related bathymetric evolution and its effects on these responses. Here, it is shown how observations, theory and model studies can be used to understand these evolving interactions between tidal dynamics, sediment regime, and bathymetry. Concentrating on the Mersey Estuary, the capabilities of a fine-resolution 3-D model are assessed against the perspective of historical changes in tides, sediments and esturarine bathymetries. New theoretical frameworks can be used to interpret ensemble simulations of parameter sensitivities. The methodologies should be applicable across a broad range of estuaries. Generally, relatively small and gradual changes are expected in most estuaries. However, conditions which might produce major abrupt changes are identified.