Zonation of wave-induced erosion threat of a sandy shoreline in central Tuscany (Italy)

Abstract

Coastal systems are among the most vulnerable areas on Earth, susceptible to both human and natural threats. They increasingly face detrimental effects, such as coastal erosion, exacerbated by a changing climate. Among several drivers of coastal retreat, wave action plays a crucial role, with more energetic waves potentially more disrupting. A method to assess wave-induced erosion threat distribution along coastal sectors over large scales and relevant times (i.e., > 20 yr), at high spatial resolution (i.e., < 100 m) is needed but remains elusive in the absence of high-resolution data. Wave reanalysis products with large spatio-temporal cover, do not properly resolve nearshore wave heights which are often negatively biased. The resulting underestimation of wave energy can propagate to nested models, causing an underrating of the resulting erosion. In this work, we propose a simplified method for the zonation of wave-induced erosion threat along a sandy coast, with large spatio-temporal cover and overcoming the limitations due to energy underestimation. Through a normalization procedure, long-term low-resolution data are employed in a zonation inference, without underestimating the results. The outcome is a set of two non-dimensional coefficients evaluated along the shoreline to evaluate its status. They separate over-threatened sections from under- threatened ones, when wave action is the main chronic erosion driver and human intervention is limited. The method is successfully compared with shoreline evolution measurements on a sandy coast over a 25-years period, providing a complementary assessment framework pertinent to coastal management, planning and mitigation on useful spatio-temporal scales.