Abstract
In previous studies, an emphasis on the particular vulnerability of small island states to future sea-level rise and the intensity of increasing storm surges have been discussed. This preliminary assessment develops a Coastal Vulnerability Index (CVI) along the 202 km-long coastline of Ngazidja Island (formerly Grande Comore, Comoros Archipelago), using fieldwork, remote sensing, and geographic information system tools (GIS). The CVI considers nine variables: geology (a), geomorphology (b), topography (c), shoreline change (d), shoreline exposure (e), relative sea-level rise (f), significant wave height (g), mean tide range (h), and land-use (i). The land-use variable was added in this analysis to highlight the human asset exposure in the surrounding areas. Each variable was ranked based on local physical and hydrodynamic conditions and their vulnerability contribution to sea-level rise. The CVI was computed in 270 sections. According to the vulnerability index, approximately 57.5% of the coastline is under low and moderate vulnerability. High and very high vulnerabilities refer specifically to beaches and shores with old volcanic lava flows located mainly in the northern, northeastern, and southeastern parts of the island, approximately 42.5% of the coastline. The lowest value of CVI is 9.2 on high, rocky cliffs and the highest value is 160 on beaches. This vulnerability partition along the coastline is consistent with in situ indicators of coastal erosion and flooding. In a sea-level rise context, it is of prime importance to integrate coastal vulnerability maps with planning and sustainable management of the coastal zone.
Highlights
IntroductionThe rate of sea-level rise is estimated at 8 to 16 mm/yr in 2100, while its estimation was only 3.2 +/- 0.4 mm/yr in the early 1990s (Cazenave et al 2015)
Climate change has compounded problems of environmental degradation in coastal zone
This assessment shows the first results of the vulnerability repartition on the Ngazidja coastline using a Coastal Vulnerability Index (CVI) vulnerability index
Summary
The rate of sea-level rise is estimated at 8 to 16 mm/yr in 2100, while its estimation was only 3.2 +/- 0.4 mm/yr in the early 1990s (Cazenave et al 2015) These increases will accentuate coastline recession, degradation of coastal ecosystems, and loss of material assets (Anderson et al 2015). The Malherbe et al study (2013) indicates an increase in rainfall in the basin subzone, between northern Mozambique and southern Tanzania, for the latter part of the 21st century This increase further emphasizes the potential coastal inundation risk. The coral reef ridges had enabled the dissipation of more than 80% of wave energy (Ferrario et al 2014) The weakening of these natural barriers prevents their attenuation efficiency of coastal hazards such as coastal erosion and marine submersion
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