Implications of sea-level rise for overwash enhancement at South Portugal

Overwash is one of the most prominent hazards affecting coastal zones, and the associated consequences are expected to increase because of both sea-level rise and intensification of coastal occupation. This study used a 23-year data set of wave heights and tide-surge levels to define return periods of overwash potential for current and future sea-level conditions, namely 2055 and 2100, at two sites from South Portugal. A relevant intensification of both frequency and magnitude of the overwash is expected to occur by mid-century if adaptation measures are not taken and further aggravated by 2100. Current overwash levels with a return period of 100-years can reach a return period lower than 20-years by 2055 and 10-years by 2100. However, these values are rather variable from site to site, highlighting the urgency to develop detailed local studies to identify climate change impacts along coastal sectors, based on validated equations and long-term time series. These could be easily carried by replicating and adapting the here proposed methodology to sandy coasts worldwide. Understating the impact that climate change (namely sea-level rise) may have at the local level is key to contribute to effective management plans that include adaptation measures to minimize risks associated with coastal floods.