World's beaches eroding in protected marine areas: NASA

The world's sandy shorelines are declining in protected marine areas which could threaten plant and animal species and cultural heritage sites, a global survey of beaches with satellite data from NASA and the US Geological Survey shows.

Worldwide, the study found that 24 per cent of Earth's sandy beaches are eroding, a coastline distance of almost 50,000 miles, NASA said in a statement.

The view from space provided a team of scientists and engineers from the Netherlands with a more accurate picture of just how much of Earth's shorelines are beaches.

They found that about a third (31 per cent) of all ice-free shorelines are sandy or gravelly. Africa has the highest proportion of sandy beaches (66 per cent) and Europe has the lowest (22 per cent).

 

The team used machine learning to "teach" its classification software to accurately identify sandy beaches from images taken by Landsat satellites from NASA and the US Geological Survey.

This allowed them to quickly and automatically examine 30 years of data and determine how many of Earth's beaches are sandy instead of rocky or icy, and how those sandy beaches are changing with time.

"It only took about two months' calculation time to generate this data set of annual shorelines between 1984 and 2016 for the entire world," said Arjen Luijendijk, a coastal development expert at Deltares, an independent research institute in the Netherlands.

"The alternative of taking aerial images, placing the images in world coordinates, and sometimes manually detecting shorelines, takes weeks or months to capture a coast longer than 50 miles," Luijendijk said.

Taking this kind of global snapshot gives scientists a clearer idea of what large scale processes govern the growth and retreat of beaches around the world, Luijendijk said.

The team found that many of the world's non-protected beaches are undergoing change too, but not uniformly. About 24 per cent of sandy beaches worldwide are eroding, while 27 per cent are growing.

Additionally, about 16 per cent of all beaches are eroding at rates designated "intense" or "extreme," and 18 per cent are growing at the same rates.

Globally, all of this averages out to a slight average increase over the last 30 years, meaning that our sum total of sandy beaches is increasing slightly.

The researchers were able to break down these results by continent to find that beaches in Australia and Africa are experiencing more erosion than growth.

The opposite is true for all other continents, where on average beaches are growing, a process scientists call accretion.

"At this point we think the continental differences in beach erosion and accretion are largely influenced by human interventions along the coast," Luijendijk said.

"Our next steps will focus on distinguishing the human impact from the natural dynamics and trends," he said.

Protected marine areas include sanctuaries and reserves, national parks, wildlife refuges and national monuments, and may be designated for their biological, ecological or cultural value.