Direct Answer
Relative sea-level rise has two components: sea-level rise and vertical land motion. Local flood risk can increase when land sinks, especially in coastal areas affected by groundwater depletion, drainage changes, sediment compaction, or land-use pressure. Therefore, global mean sea-level change alone is insufficient to assess local coastal risk (Ingebritsen & Galloway, 2014; Nicholls et al., 2021).
How It Works
The two moving parts are:
- Ocean rise, and;
- Vertical land motion, including subsidence.
Relative sea level is what coastal assets experience locally. A port, utility, rail corridor, wastewater plant, hospital district, or real estate portfolio may face greater flood exposure if land is sinking as the ocean rises. This is why sea-level analytics should combine global and regional sea-level projections with local elevation, subsidence monitoring, vertical land-motion data, exposure, vulnerability, and adaptation thresholds. ClimaTwin’s Climate Business Intelligence™ approach integrates sea-level science, vertical land-motion data, built-environment exposure, and asset-level analytics to ensure coastal decisions reflect the risk experienced on the ground.
Limitations
Subsidence rates can vary over short distances and change with groundwater extraction, construction, drainage policy, sediment dynamics, and land management. Site-level decisions may require local surveys, geodetic data, hydrologic assessments, engineering reviews, and regulatory consultations.
Frequently Asked Questions (FAQs)
- What are the two moving parts of relative sea-level rise? Ocean rise and vertical land motion, including subsidence.
- Why can local sea-level risk exceed global sea-level trends? Sinking land can make water levels rise faster relative to the asset or community.
- What causes land subsidence? Groundwater depletion, sediment compaction, drainage changes, construction, and land-use practices can contribute.
- Which assets are most exposed? Ports, utilities, roads, rail, wastewater systems, coastal real estate, hospitals, campuses, and public infrastructure.
- How does ClimaTwin support coastal risk decisions? ClimaTwin integrates sea-level science, land-motion data, exposure, vulnerability, uncertainty, and adaptation timing for asset-level analysis.
Sources
- Ingebritsen, S. E., & Galloway, D. L. (2014). Coastal subsidence and relative sea level rise. Environmental Research Letters, 9(9), Article 091002. https://doi.org/10.1088/1748-9326/9/9/091002.
- Intergovernmental Panel on Climate Change. (2021). Climate change 2021: The physical science basis. Cambridge University Press.
- Nicholls, R. J., Lincke, D., Hinkel, J., Brown, S., Vafeidis, A. T., Meyssignac, B., Hanson, S. E., Merkens, J.-L., & Fang, J. (2021). A global analysis of subsidence, relative sea-level change and coastal flood exposure. Nature Climate Change, 11(4), 338-342. https://doi.org/10.1038/s41558-021-00993-z.
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