Numerical modelling of storm tides in the Estuarine System of Santos, São Vicente and Bertioga (SP, Brazil)

Abstract

A set of three nested hydrodynamic models was carried out, from part of Southeastern Brazilian shelf towards the Estuarine System of Santos, São Vicente and Bertioga (ESSSVB), to reproduce the storm tides in which the Civil Defence alert status was reached throughout 2016, known for the occurrence of severe storm surges. The ESSSVB model – called Level 2 – has 80 m grid resolution and is nested into an intermediary grid — Level 1, which in turn is nested into a mesoscale grid comprising part of Southeastern Brazilian shelf – Level 0, all of them with a vertical discretisation of 12 sigma layers. The model grids are forced by tides, winds, elevation, temperature, salinity and river discharge. Furthermore, a detailed bathymetry is employed considering the mangrove areas. The simulations results lead to an average sea-level skill score of 0.96, with an average root mean square error (RMSE) of 0.15 m. For the along-channel component at each station analysed, the average skill and RMSE were 0.84 and 0.19 m/s. In 2016, five events reached the alert status; in these events, the simulations underestimated the surge in approximately 0.11 m, with average skill and RMSE of 0.96 and 0.15 m The peak errors reached 0.20 m at Palmas and 0.34 m at Barnabé, revealing the importance of more precise freshwater inputs and meteorological forcing. Nevertheless, although the modelled storm surges were below the observed values, the agreement with data reveals that this model setup can be used in early warning systems, therefore helping local civil defences in decision making. The model evaluation indicates an important improvement when compared to the operational two-dimensional model. Another important objective here achieved was the reproduction of storm tides produced by different patterns of astronomical and meteorological forcing, especially extratropical cyclones formation and displacement.