WELLINGTON, June 11 (Xinhua) -- Human-driven sea-level rise has made coastal flooding in New Zealand's capital of Wellington far more likely, with once-rare "1-in-100-year" floods now occurring about twice a year, new research reveals.

A study published in Nature Climate Change found that sea-level rise has made extreme coastal water levels about four times more frequent globally since 1900. Events that historically had a 1-percent annual chance of occurring have, at many sites, become at least ten times more likely by 2005.

It comes after Wellington lifted this week a local state of emergency for parts of the capital following large swell warnings for the south coast and southern Wairarapa region.

Scientists attribute most of the increase to human-driven climate change, which has raised global mean sea levels by about 20 cm over the past century. Higher baseline sea levels mean that tides and storm surges more easily exceed flooding thresholds, Scott Stephens, chief scientist at Earth Sciences New Zealand, said Thursday in his comment.

Rob Bell, research associate at the University of Waikato in New Zealand, said Wellington's relatively small tidal range and limited storm-tide variability mean even a small amount of sea-level rise can rapidly escalate flood frequency.

Researchers warn that continued sea-level rise will further increase coastal flood risk, underscoring the need for updated flood planning and adaptation measures, particularly in low-lying coastal communities.

"This week's extreme wave event on the Wellington south coast reinforces the idea that we need to act now and develop response plans urgently," said Professor James Renwick at Victoria University of Wellington.