Pacific Island nations such as Tuvalu, Kiribati and Fiji will experience at least 20 centimetres of sea level rise in the next 30 years regardless of whether greenhouse gas emissions change in the short term, according to new research from NASA.

The analysis found that the number of high-tide flooding days — otherwise known as nuisance flooding or sunny day flooding (a temporary inundation of low-lying areas, especially streets) — in an average year will increase significantly for nearly all Pacific Island nations by the 2050s.

A new agreement allowing Tuvaluans to migrate to Australia has come into effect but there are warnings about the challenges that come with such a big move.

For example, areas of low lying island Tuvalu that currently see less than five high-tide flood days a year could average 25 flood days annually by the 2050s.

In Kiribati, regions that see fewer than five flood days a year today will experience an average of 65 flood days annually by the 2050s, according to the research.

The NASA Earth Science Division's ocean physics program director, Dr Nadya Vinogradova Shiffer, said their findings provided a clearer picture of what "flooding frequency and severity look like" over the coming decades.

"Sea level will continue to rise for centuries, causing more frequent flooding," she said.

The effects of sea level rise differ across the world due to several factors including global and local conditions, the topography of a coastline and how glacial meltwater is distributed in the ocean.

However, Pacific Island nations face more dire circumstances compared to the rest of the world.

"We're always focused on the differences in sea level rise from one region to another, but in the Pacific the numbers are surprisingly consistent," said Ben Hamlington, a sea level researcher at NASA's Jet Propulsion Laboratory in California and the agency's sea level change science team lead.

Airports at risk of regular flooding

NASA's research found that impacts of a 20-centimetre rise in sea level will also vary from country to country in the Pacific Islands.

For instance, some nations might face frequent neighbourhood flooding equivalent to being inundated for nearly half the year.

Others could experience nuisance flooding several times a year at their airport.

The agency’s sea level team released high-resolution maps this week showing which areas of different Pacific Island nations will be vulnerable to high-tide flooding.

The maps outline flooding potential in a range of emissions scenarios, from best-case to business-as-usual to worst-case.

Researchers at several universities including the University of Hawaii and Virginia Tech, started with flood maps of Kiribati, Tuvalu, Fiji, Nauru and Niue.

They plan to build high-resolution maps for other Pacific Island nations in the near future, aimed at supporting mitigation efforts.

Researchers said their aim to combine satellite data on ocean levels with ground-based measurements of sea levels at specific points are hindered.

"There's a real lack of on-the-ground data in these [Pacific Island] countries," Mr Hamlington said.

NASA's research was conducted at the request of several Pacific Island nations, including Tuvalu and Kiribati, and in coordination with the US State Department.

While scientists say rising sea levels will bring significant impacts to Pacific Island nations, some research has shown hundreds of islands in the Pacific are growing in land size due to sediment, corals and other debris being washed ashore.

This article was first published on ABC Pacific Beat.