Sandy shorelines increase marginally over three decades

Global study of satellite data shows threat to protected areas

A first-of-its-kind survey of the world’s sandy shorelines with satellite data found that they have increased slightly on a global scale over the past three decades but decreased in protected marine areas, where many beaches are eroding.

Cape Cod National Seashore is a protected marine area, home to a variety of ecosystems with diverse plants and animals.

Cape Cod National Seashore is a protected marine area, home to a variety of ecosystems with diverse plants and animals.

Erosion in protected marine areas could threaten plant and animal species and cultural heritage sites. Worldwide, the study found that 24 percent of Earth’s sandy beaches are eroding, a coastline distance of almost 50,000 miles.

The view from space provided researchers with a more accurate picture of just how much of Earth’s shorelines are beaches. They found that about a third (31 percent) of all ice-free shorelines are sandy or gravelly.

Africa has the highest proportion of sandy beaches (66 percent) and Europe has the lowest (22 percent).

A team of scientists and engineers from the Netherlands used machine learning to “teach” their classification software to accurately identify sandy beaches from images taken by Landsat satellites from NASA and the U.S. 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.

In the past, answering these questions required years of expensive, labor-intensive research, and the results of previous attempts to measure Earth’s beaches varied widely.

“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 studying deltas, river basins and coasts.

“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.”

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 percent of sandy beaches worldwide are eroding, while 27 percent are growing.

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