CLIMATE CHANGE AND TROPICAL COASTAL VULNERABILITY IN THE GULF OF GUINEA, NIGERIA.

Coastal regions are essential spots on earth as they are hosts to various important ecosystems, natural resources, and an increasing population. They are mainly affected by sea-level rise, which is one of the effects of climate change. This study quantifies and classifies the vulnerability of the Nigerian coastline to increase in sea levels. This involved calculating the coastal vulnerability index (CVI) employing physical and geomorphological variables, and socioeconomic indicators that characterized the coastline vulnerability. Two approaches were utilized in this study to obtain the Coastal Vulnerability Index (CVI): an analytical hierarchical process (AHP) based approach to coastal vulnerability studies and the CVI formula proposed by Gornitz (1991). 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 1 indicating the lowest and 5 indicating the highest 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. Also, the trends and effects of some ocean variables of the Nigerian coastline were analysed, with the aim of identifying the potential drivers of sea level changes. This was achieved by the analysis of tide and oceanographic data obtained from both local and international agencies. Statistical analysis was carried out using MATLAB and XLSTAT. Sea level change projection was carried out using simCLIM. A comparison of CVI values was carried out and the AHP based approach appeared to be a more realistic approach in assessing coastal vulnerability as it is systematic and stepwise. The calculated CVI values (AHP method) ranged from 11.25 to 41.66 with a median value of 23.60. Based on Gornitz approach, the calculated values 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. These data indicated how the coastal populations are highly vulnerable to both physical–geomorphological and socioeconomic stressors. Coastal vulnerability maps, highlighting the various ranking regions with low, moderate, and high vulnerability were generated in this study. The median projected sea-level rise values using simCLIM ranged from 11.86 cm to 49.22 cm for RCP 2.6; 11.73 cm to 58.91 cm for RCP 4.5; 11.28 cm to 62.28 cm for RCP 6.0; 11.92 cm to 84.25 cm for RCP 8.0, respectively. From the results of this study, there is evidence of rise in sea level occurring in the Nigerian coastline. The projections also predict a continuous increase in sea level in the coming years. Therefore, the results obtained from this study would assist coastal planners in the identification of vulnerable regions along the Nigerian coastline and subsequently influence decisions that would mitigate the predicted impacts of the associated hazards of climate change in the regions