From InSAR‐derived subsidence to relative sea‐Level rise - A call for rigor
P. S. J. Minderhoud
Soil Geography and Landscape group,
Wageningen University & Research,
Wageningen, The Netherlands
M. Shirzaei
Department of Geosciences, Virginia Tech, Blacksburg, VA, USA
P. Teatini
Dept. of Civil, Environmental and Architectural Engineering, University of Padova, Padova, Italy
ABSTRACT
Coastal subsidence, the gradual sinking of coastal land, considerably exacerbates the impacts of
climate change-driven sea-level rise (SLR). While global sea levels rise, land subsidence often increases relative
SLR locally. Thieblemont et al. (2024, https://doi.org/10.1029/2024ef004523) reached a remarkable milestone
by providing a continental-scale estimate of vertical land motion (VLM) across European coastal zones by
utilizing European Ground Motion Service (EGMS) data, obtained from Interferometric Synthetic Aperture
Radar (InSAR) data from Sentinel-1 satellites. Their findings reveal widespread coastal subsidence, with nearly
half of the coastal floodplains, including major cities and ports, subsiding at rates exceeding 1 mm/yr, thereby
exacerbating relative SLR. The study emphasizes the critical role of InSAR-data calibration, indicating that the
EGMS geodetic reference frame significantly influences VLM estimates. This study highlights the need for a
robust InSAR-data processing framework to accurately interpret VLM and its relationship to relative SLR. The
processing pipeline should ensure internal consistency of SAR data and rigorously assess output accuracy,
considering also post-processing effects. Correct interpretation of results is essential as InSAR satellites
measure reflector movement, which may not always align with land surface movement, particularly in urban
areas. Ignoring these discrepancies can lead to underestimation of subsidence rates. While InSAR data offers
valuable research opportunities, it poses risks of oversimplification and misinterpretation, especially when
linked to sea-level change. We call for standardized processing workflows and cross-disciplinary collaboration,
essential for accurate VLM interpretations, particularly in coastal cities and river deltas, to ultimately enhance
the reliability of relative SLR projections and inform effective coastal management strategies.
