Land subsidence dynamics and their interplay with spatial and temporal land-use transitions in the Douala coastland, Cameroon
G. Y. Chounna, P. Teatini
Dept. of Civil, Environmental and Architectural Engineering, University of Padova, Padova, Italy
P. S. J. Minderhoud
Soil Geography and Landscape group, Wageningen University & Research, Wageningen, The Netherlands
L. Ohenhen
University of California, Irvine, Irvine, CA, USA
K. Seeger
Institute of Geography, University of Cologne, Cologne, Germany
M. Shirzaei
Department of Geosciences, Virginia Tech, Blacksburg, VA, USA
ABSTRACT
The Douala coastland (DCL), situated within the
Douala sedimentary basin along the Gulf of Guinea, is characterised by its low elevation and alluvial geology, making it
particularly susceptible to coastal erosion, land subsidence,
and relative sea-level rise. The DCL is home to numerous
rapidly growing cities, such as Douala, Tiko, and Limbe,
which are currently experiencing alarming rates of coastal
erosion, frequent flooding, and significant loss of land. Regional and continental investigations have provided evidence
of coastal subsidence in this region; however, knowledge of
its drivers and impact on the DCL remains limited. To address this knowledge gap, interferometric synthetic aperture
radar (InSAR) datasets from the Sentinel-1 C-band satellite
were used to quantify vertical land motion (VLM) between
2018 and 2023 with respect to the IGS14 global reference
frame and assumed to represents absolute VLM. Digital Elevation Model datasets were used to analyse the elevation
of the study area. The results revealed that the rate of VLM
ranges from -17.6 to 3.8 mm yr-1 (standard deviation of
0.2 mm yr-1), with a mean and median land subsidence rate
of 2.7 and 2.5 mm yr-1. The analysis of land cover datasets
from 1992 to 2022 suggests that urbanisation increased fivefold from 1992 to 2022 and that all contemporary urban areas
experienced land subsidence, with the highest rates observed
in non-residential zones with building heights ranging between 3 and 6 m. Subsidence rates of the DCL are inversely
proportional to the time at which a particular land use and
land cover (LULC) class changed into an urban area, highlighting the impact of the timing of LULC changes and urban
expansion on present-day subsidence. The land subsidence
rates decreased with an increase in building height, suggesting shallow land subsidence, where tall building usually with
deep foundations are less prone to subsidence caused by
groundwater extraction from the phreatic aquifer
