Coastal Vulnerability Index (CVI) Assessment of a Data-Sparse Delta: Quantifying the Contribution of InSAR-Derived Land Subsidence in the Volta Delta, Ghana.
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| Title: | Coastal Vulnerability Index (CVI) Assessment of a Data-Sparse Delta: Quantifying the Contribution of InSAR-Derived Land Subsidence in the Volta Delta, Ghana. |
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| Authors: | Avornyo, Selasi Yao1 (AUTHOR), Bonì, Roberta2 (AUTHOR) roberta.boni@iusspavia.it, Ikuemonisan, Femi Emmanuel3 (AUTHOR), Jayson-Quashigah, Philip-Neri4 (AUTHOR), Okyere, Obed Omane4,5 (AUTHOR), Kwame-Biney, Michael1,6 (AUTHOR), Minderhoud, Philip S. J.5,6,7 (AUTHOR), Mahu, Edem1 (AUTHOR), Teatini, Pietro2,6 (AUTHOR), Appeaning Addo, Kwasi1,3 (AUTHOR) |
| Source: | Remote Sensing. Sep2026, Vol. 18 Issue 17, p3042. 28p. |
| Subjects: | Land subsidence, Radar interferometry, River deltas, Sea level, Coasts |
| Geographic Terms: | Ghana |
| Abstract: | Highlights: What are the main findings? Including measured subsidence, InSAR-derived land subsidence in the Coastal Vulnerability Index raised the mean vulnerability of the Volta Delta's coastline from moderate to very high, with 75% of grid cells rated as high or very high once locally measured subsidence was accounted for, compared with 44% using the regional estimate and 28% when subsidence was left out. A mean subsidence rate of about 3.35 mm/yr roughly doubles the local rate of relative sea-level rise against a regional rise of 4 to 5 mm/yr, and the highest vulnerability consistently falls along the lagoonal margins. What are the implications of the main findings? Deltaic coastal vulnerability assessments that assume global average subsidence rates understate the real exposure of subsiding deltas and can misdirect where adaptation funding is placed. Where subsidence has an anthropogenic component, it becomes a hazard that can be managed at its source rather than only defended against, especially at the worst hotspots where hard engineering defences risk worsening erosion downdrift and blocking the landward retreat of coastal ecosystems. 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. [ABSTRACT FROM AUTHOR] |
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| Database: | Engineering Source |
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| Abstract: | Highlights: What are the main findings? Including measured subsidence, InSAR-derived land subsidence in the Coastal Vulnerability Index raised the mean vulnerability of the Volta Delta's coastline from moderate to very high, with 75% of grid cells rated as high or very high once locally measured subsidence was accounted for, compared with 44% using the regional estimate and 28% when subsidence was left out. A mean subsidence rate of about 3.35 mm/yr roughly doubles the local rate of relative sea-level rise against a regional rise of 4 to 5 mm/yr, and the highest vulnerability consistently falls along the lagoonal margins. What are the implications of the main findings? Deltaic coastal vulnerability assessments that assume global average subsidence rates understate the real exposure of subsiding deltas and can misdirect where adaptation funding is placed. Where subsidence has an anthropogenic component, it becomes a hazard that can be managed at its source rather than only defended against, especially at the worst hotspots where hard engineering defences risk worsening erosion downdrift and blocking the landward retreat of coastal ecosystems. 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. [ABSTRACT FROM AUTHOR] |
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| ISSN: | 20724292 |
| DOI: | 10.3390/rs18173042 |
