The significance of vertical land movements at convergent plate
boundaries in probabilistic sea-level projections for AR6 scenarios: The
New Zealand case.
Abstract
Anticipating and managing the impacts of sea-level rise for nations
astride active tectonic margins requires rates of sea surface elevation
change in relation to coastal land elevation to be understood. Vertical
land motion (VLM) can either exacerbate or reduce sea-level changes with
impacts varying significantly along a coastline. Determining rate,
pattern, and variability of VLM near coasts leads to a direct
improvement of location-specific relative sea level (RSL) estimates.
Here, we utilise vertical velocity field from interferometric synthetic
aperture radar (InSAR) data, calibrated with campaign and continuous
Global Navigation Satellite System (GNSS), to determine the VLM for the
entire coastline of New Zealand. Guided by existing knowledge of the
seismic cycle, the VLM data infer long-term, interseismic rates of land
surface deformation. We build probabilistic RSL projections using the
Framework for Assessing Changes to Sea-level (FACTS) from IPCC
Assessment Report 6 and ingest local VLM data to produce RSL projections
at 7435 sites, thereby enhancing spatial coverage that was previously
limited to tide gauges. We present ensembles of probability
distributions of RSL for medium confidence climatic processes for
each scenario to 2150 and low confidence processes to 2300. For
regions where land subsidence is occurring at rates >2mm
yr-1 VLM makes a significant contribution to RSL
projections for all scenarios out 2150. Beyond 2150, for higher
emissions scenarios, the land ice contribution to global sea level
dominates. We discuss the planning implications of RSL projections,
where timing of threshold exceedance for coastal inundation can be
brought forward by decades.