Sea level rise in New Zealand refers to the increase in average sea level around the country’s coasts as a result of global climate change. Tide‑gauge and satellite records show that sea levels around New Zealand have risen at rates similar to the global average, though local trends vary because of vertical land movement from tectonic processes and subsidence. National projections indicate that sea levels will continue to rise throughout the 21st century under all emissions scenarios, with some regions expected to experience substantially higher relative sea‑level rise where land is sinking. Sea‑level rise contributes to more frequent coastal flooding, shoreline erosion, saltwater intrusion, and impacts on infrastructure, housing, and low‑lying ecosystems. These effects are expected to get worse as sea levels rise, particularly in major urban areas and subsiding coastal plains. Local authorities and central government agencies have developed adaptation frameworks, hazard assessments, and long‑term planning tools to manage these risks, including managed retreat in some locations.
Overview Sea level rise in New Zealand poses a significant threat to many communities, including New Zealand's larger population centres, and has major implications for infrastructure in coastal areas. In 2016, the Royal Society of New Zealand stated that a one-metre rise would cause coastal erosion and flooding, especially when combined with storm surges. Climate scientist Jim Salinger commented that New Zealand will have to abandon some coastal areas when the weather gets uncontrollable. Twelve of the fifteen largest towns and cities in New Zealand are coastal with 65% of communities and major infrastructure lying within five kilometres of the sea. The value of local government infrastructure that is vulnerable to sea level rise has been estimated at $5 billion. As flooding becomes more frequent, coastal homeowners will experience significant losses and displacement. Some may be forced to abandon their properties after a single, sudden disaster like a storm surge or flash flood or move away after a series of smaller flooding events that eventually become intolerable. Local and central government will face high costs from adaptive measures and continued provision of infrastructure when abandoning housing may be more efficient. The results of studies from a programme called NZ Searise released in 2022, indicate that for some parts of New Zealand, the apparent sea level rise will be twice as fast as previously predicted. This is because of the combined effect of absolute rise in sea level with gradual subsidence of ground levels. In some parts of Wellington, the land is subsiding by 3–4 mm per year, leading to an apparent 30 cm of sea-level rise in 18 years. By 2040, this is forecast to cause inundations every year that are equivalent to a 1-in-100 year event in 2020.
Twentieth century An analysis in 2004 of long term records from four New Zealand tide gauges indicated an average rate of increase in sea level of 1.6 mm a year for the 100 years to 2000, which was considered to be relatively consistent with other regional and global sea level rise calculations when corrected for glacial-isostatic effects. One global average rate of sea-level rise is 1.7 ± 0.3 mm per year for the 20th century (Church and White (2006). Another global average rate of sea-level rise is 1.8 mm/yr ± 0.1 for the period 1880–1980. A 2008 study of cores from salt-marshes near Pounawea indicated that the rate of sea level rise in the 20th century, 2.8 ± 0.5 mm per year, had been greater than rate of change in earlier centuries (0.3 ± 0.3 mm per year from AD 1500 to AD 1900) and that the 20th century sea level rise was consistent with instrumental measurements recorded since 1924.
… excerpt ends here. Continue reading the full article.
