In a recent study published in Communications Earth & Environment, researchers at the University of Hawaii at Mānoa reported that certain coastal areas in the Hawaiian Islands are sinking at a significantly faster rate than previously anticipated, moving up the need for flood preparedness by about 50 years. The phenomenon, known as subsidence, poses a substantial threat to businesses, residents and infrastructure, as sea level rise exacerbates the risks of flooding, beach loss and coastal erosion.

The scientists observed that the island of Oahu is sinking at an average rate of 0.6 millimeters per year, while its south shore has localized subsidence rates exceeding 25.0 millimeters per year, which is substantially faster than Hawaii’s long-term sea level rise rate of 1.54 millimeters per year since 1905. The south shore encompasses Waikiki beach and the city of Honolulu. The confluence of subsidence and sea level rise places $12.9 billion of local infrastructure at risk from flooding.

Subsidence can be caused by a number of different processes, including sediment compaction, tectonic motion and earthquakes, volcanic deformation, melting of permafrost and peat-land degradation, as well as human activities such as groundwater extraction, hydrocarbon production, mining and geothermal activity