Sinking US cities vulnerable to sea-level rises

A considerable amount of land in 32 US coastal cities, including Boston, New Orleans, and San Francisco, could be at risk of flooding by 2050, according to international researchers. The findings, which are supported by flooding models and also take into account land sinking, indicate that 55,000 to 273,000 people and 31,000 to 171,000 properties could be affected. If no effective flood-defence structures are implemented, their model suggests that relative sea-level rise could expose a further land area between 1,334 and 1,813 km2. In a worst-case scenario, this could expose 1 in every 50 people along the US coast to a flood threat, they say.

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From: Springer Nature

Environmental sciences: Sinking US cities are more vulnerable to sea-level rises

A considerable amount of land in 32 US coastal cities could be at risk of flooding by 2050, a paper published in Nature suggests. The findings, which are supported by flooding models, indicate that 55,000 to 273,000 people and 31,000 to 171,000 properties may be affected as a result. The estimates consider subsidence, which has been underrepresented in previous models.

Under current projections, sea levels are expected to rise faster than the global average in US coastal cities, where more than 30% of the US population resides. The resulting inundation of coastal cities may be worsened owing to coastal subsidence (the sinking of land), which is often overlooked in coastal management policies and long-term urban planning.

Leonard Ohenhen and colleagues combine models of land elevation changes and projected sea-level rise to estimate the risk of flooding in 32 US cities, including Boston, New Orleans and San Francisco, by 2025. If no effective flood-defence structures are implemented, their model suggests that relative sea-level rise could expose a further land area between 1,334 and 1,813 km2. In a worst-case scenario, this could expose 1 in every 50 people along the US coast to a flood threat.

Coastal areas with higher elevation levels and lower rates of subsidence, such as the Pacific Coast, are found to have a lower flood threat overall. Areas with lower elevation levels and higher rates of subsidence, such as New Orleans on the Gulf Coast, are found to be at higher risk. The Atlantic Coast is found to be most exposed, owing in part to its lack of adequate flood protection. Where flood measures are present, higher levels of subsidence affect their effectiveness and structural integrity.

When taking current defence structures into account, the authors observe that by 2050 relative sea rise may still affect an area of 1,006 to 1,389 km2. As coastal land continues to sink each year, the authors propose that current hazard mitigation is inadequate. Improved flood defences and subsidence control measures must be made to current coastal defense systems, they add.

These potential consequences reveal the scale of the adaptation challenge, which is largely unappreciated in most US coastal cities. The growing risks of relative sea-level rise identified in this paper pose a major challenge to communities, especially disadvantaged populations who are already disproportionally struggling with climate change inequalities. The authors conclude that datasets and inundation hazard maps may critically inform risk management and contribute to the development of proactive and effective adaptation.

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