Coastal Vulnerability Assessment: A Case Study of the Nigerian Coastline

Abstract

Coastal regions are one of the essential spots on the earth as they are hosts to various important ecosystems, natural resources and the increasing population. Based on their proximity to the seas, they are mainly affected by sea-level rise, which is one of the adverse effects of climate change. This has resulted in associated hazards, such as beach erosion, flooding, coastal inundation, habitat destruction, saltwater intrusion into ground water aquifers and ecosystem imbalance. This study quantifies and classifies the vulnerability of the Nigerian coastline to these threats using the analytical hierarchical approach. This involved calculating the coastal vulnerability index (CVI) employing physical and geomorphological variables, and socioeconomic indicators that characterized the coastline vulnerability. The Nigerian coast was divided into seventeen (17) segments based on geomorphic units. The different vulnerability variables were assigned ranks ranging from 1 to 5, with 5 indicating the highest and 1 indicating the lowest vulnerabilities. The geomorphological and physical parameters include coastal slope, bathymetry, geomorphology, wave height, mean tidal range, shoreline change rate and relative sea-level rise, while the socioeconomic parameters include population, cultural heritage, land use/land cover and road network. The calculated CVI values (Saaty method) ranged from 11.25 to 41.66 with a median value of 23.60. Based on Gornitz approach, the calculated measures ranged between 3.51–4.77 and 3.08–5.00 for PVI and SoVI, respectively. However, the aggregated coastal vulnerability index computed using this approach ranged from 3.29 to 4.70. The results obtained from both approaches showed that 59–65% of the entire Nigerian coastline is under moderate to high vulnerability to sea-level rise. Data indicted how the coastal populations are highly vulnerable to both physical–geomorphological and socioeconomic stressors. Coastal vulnerability maps, highlighting the physical–geomorphological and socioeconomic vulnerability status of Nigerian coastline were also generated. The information from this study will assist coastal planners in identifying vulnerable segments in the study area and subsequently aid decisions that would mitigate the predicted impacts in the region.