Multi-criteria evaluation approach to coastal vulnerability index development in micro-tidal low-lying areas

• A CVI method for low-lying micro-tidal coastal segments developed.
• The method relies almost exclusively on geological variables.
• An AHP method used to incorporate experts' judgements'.
• About 10% of the Lithuanian coast is under very high risk.

The coastal zones face much higher risks disasters and vulnerability to natural and anthropogenic forcing because of their location in extremely high-energy and rapidly developing environment. We develop and implement an updated set of indicators of coastal vulnerability that characterise relatively low-lying coastal segments with negligible tidal range but affected by substantial storm surges driven by atmospheric factors. The study area is about 90 km long coast of Lithuania in the south-eastern Baltic Sea. The classical methods for building the coastal vulnerability index (CVI) are combined with the outcome analytical hierarchical process (AHP) based approach for incorporating experts' judgements to specify the weights of used criteria. The CVI relies mostly on geological parameters (shoreline change rate, beach width/height, underwater slope, sand bars, and beach sediments) and involves only significant wave height as the representative of direct physical drivers. The selected criteria were integrated into CVI calculation using two options: (I) all criteria contribute equally, (II) each criteria may have a different contribution. Based on the weights and scores derived using AHP vulnerability maps are prepared to highlight areas with very low, low, medium, high and very high vulnerability. CVIw calculation based on option II highlighted 32% of the coast being of very high to high vulnerability, 22% of moderate vulnerability and 41% of low to very low vulnerability. Although these numbers vary to some extent depending on the viewpoint, in general about 10% of the coast in the study area is under very high risk, which calls for urgent planning and protective measures.