A scopingbution of coastal land subsidence to potential sea-level rise impact in data-sparse settings:
The case of Ghana's Volta delta
S. Y. Avornyo, M. Kwame-Biney, E. Mahu, K. Appeaning-Addo
Department of Marine and Fisheries Sciences, University
of Ghana, Accra, Ghana
R. Boni'
Dept. of Science, Technology and Society, University School for Advanced Studies (IUSS), Pavia, Italy
F. E. Ikuemonisan
Department of Physics, Lagos State University of Education, Lagos, Nigeria
P.-N. Jayson-Quashigah, O. O. Okyere
Institute for Environment and Sanitation Studies, University of Ghana, Accra, Ghana
P. Minderhoud
Soil Geography and Landscape Group, University
of Wageningen, Wageningen, The Netherlands
P. Teatini
Dept. of Civil, Environmental and Architectural Engineering,
University of Padova, Padova, Italy
Land subsidence amplifies the impacts of sea-level rise (SLR) in low-lying deltas, yet
some Coastal Vulnerability Index (CVI) assessments omit this or rely on global estimates,
drastically understating deltaic vulnerability. This study presents the first CVI assessment
along Ghana's coast to integrate validated, spatially resolved land subsidence derived from
Persistent Scatterer Interferometric Synthetic Aperture Radar (PS-InSAR). Nine geological,
geomorphological, hydrodynamic, and anthropogenic variables were quantified across
72 contiguous grid cells spanning ~150 km of the Volta Delta's coastline and ranked on a
1-5 vulnerability scale. Three composite indices were computed using a common quantile
distribution: an index excluding subsidence (CVI-sub), an index with a spatially uniform
regional vertical land motion (CVI+(u-sub)), and an index incorporating spatially resolved
local InSAR subsidence (CVI+(v-sub)). High to very high vulnerability ranks rose from
28% of cells without subsidence, through 44% with the regional estimate, to 75% with
the local InSAR; every grid cell recorded a higher CVI once subsidence was incorporated
(Wilcoxon signed-rank test, p<0.001). Vulnerability peaked along the Keta and Songor
lagoonal margins. Omitting measured subsidence understates deltaic vulnerability, and
this approach offers a transferable method for data-sparse deltas.
