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, E. Mahu, M. Kwame-Binly, K. Appeaning-Addo
Department of Marine and Fisheries Sciences, 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
K. Sieger
Institute of Geography, University of Cologne, Cologne, Germany
L. T. Hauser
Department of Geography, University of Zurich, Switzerland
M.-N. Woillez
AFD, French Development Agency, Paris, France
P. N. Jayson-Quashigah
Institute for Environment and Sanitation Studies, University
of Ghana, Accra, Ghana
Deltas are highly valuable environmental systems, ensuring various livelihoods through their ecosystem services.
However, human impact and climate change stressors are impacting deltas immensely. Consequently, many
deltas, including Ghana's Volta Delta, are facing increasing risks, especially as hazards are increasing in
magnitude and impacting coastal livelihoods. To provide a better understanding of coastal hazards in the Volta
Delta, this study assessed the Delta's subsidence regime and its consequences for the potential impact of sea-level
rise (SLR). Using the Interferometric Synthetic Aperture Radar (InSAR) technique and Global Navigation Satellite
System (GNSS) surveys, vertical land motion (VLM) was documented. Interferograms of Sentinel-1 data from
2016 to 2020 indicated subsiding rates of up to -9.2 mm/yr. By combining local VLM information with recent
SLR projections and elevation data, this study updates those projections and provides local assessments of potential
Relative SLR (rSLR) impact. According to these locally improved scenarios, up to ~45% of the Delta will
fall below local sea level by 2100, of which close to 10% is explained by the integration of local VLM data alone.
Depending on the climate change scenarios used, land subsidence will increase the deltaic area at risk by 4.31%
(96.27 km2) to 10.18% (227.64 km2) and consequently exacerbate its exposure to coastal inundation. To avert
the projections, the study recommends robust monitoring regimes; alternative freshwater sources to groundwater;
reduced sediment trapping and river obstruction; and the need to stall ongoing oil and gas prospecting and
subsequent extraction in the Voltain Basin.
