Tsunamis in the Mediterranean Sea have been increasingly investigated in the last decades due to past destructive events. We present a novel approach for evaluating tsunami-induced coastal inundation, based on a generalization of Green’s law and a chain of intermediate and small-scale numerical simulations. At the intermediate level, simulations with a linear solver are made to identify the coastal distribution of a novel parameter, namely α, condensing all nearshore wave transformations other than shoaling. α represents a proxy for coastal susceptibility to the tsunami impact. Small-scale modelling of coastal flooding performed in the southern Italy on a freely available DTM at the Esaro river estuary (Calabria) yields inundation levels that compare well with those obtained via intermediate-scale modelling, with a saving in computational time of about 41%. This demonstrates the helpfulness of α to “scale” the offshore wave input and reduce the computational effort to evaluate flooding at regional scale.

Numerical simulations of a range of wave climates and tide conditions made with the model XBeach are exploited to study propagation, evolution, dissipation, and reflection patterns of infragravity waves (IGW) at the intermediate-to-dissipative beach of Sabaudia (Tyrrhenian sea, Italy). On the basis of a novel calibration process performed using field swash properties collected by a nearby monitoring station, the model reproduces swash characteristics with good skill (Willmott index of agreement D = 0.61-0.79). IGW at Sabaudia beach evolve exclusively as bound long waves (BLW) growing across the shoaling region for both mild and intense wave climate. BLW release occurs still in the inner shoaling zone and, thus, may not be strictly connected with wave breaking inception, as usually assumed. Furthermore, values of the dimensionless bed slope βH at which transition from steep- to mild-slope behaviour occurs are higher that traditional threshold. Finally, although the small tide (0.4 m between MHWS and MLWS; tide range/breaking wave amplitude ratios between 0.14 and 1.1) does not alter bulk IGW reflection significantly, low tide is effective in reducing onshore IGW fluxes and, ultimately, reflection coefficients R2 selectively for intermediate IG frequencies. Our study, for the first time, gives clear evidence that the tide has a role in determining frequency-dependent IGW dynamics and altering the dissipative state of a mild sloping beach also in a microtidal environment.