Determining local scale extreme sea level elevation at the open coast of Côte d’Ivoire: Case study of the Bay of Port-Bouët

Abstract The bay of Port-Bouët is threatened by extreme sea level (ESL) events, which result from the combination of storm tide, wave runup and sea level rise (SLR). This study provides comprehensive present-day and future ESL elevation scenarios at local scale along the bay, to understand the evolution of the phenomenon and promote adaptation at neighbourhood level. The methodological steps involve firstly, a reconstruction of historical storm tide and wave runup data using respectively a hydrodynamic model (D-flow FM) and the empirical model of Stockdon et al. Secondly, the generalised pareto distribution (GPD) model fitted to the peaks-over-thresholds (POT) method is applied on the data to calculate their extreme return values. Thirdly, we combine extreme storm tide and wave runup through the joint probability method to obtain present-day ESLs. Lastly, the present-day ESLs are integrated with the recent SLR projection to provide ESL estimates for the years 2030, 2050 and 2100. Results show that the present-day ESL are relatively high with the 100-year return levels being 4.37m, 4.97m and 4.48m at Vridi, Petit-Bassam and Sogephia respectively. Future SLR is expected to increase the current ESL elevations by 0.49m, 0.62m or 0.84m by 2100 depending on the climate change scenarios. The developed ESL scenarios can be used to assess potential coastal flood risk in the study area for sustainable and effective coastal management and future planning.