TEPIC, Mexico, April 28 (Thomson Reuters Foundation) - If your idea of a perfect holiday is to feel the sand between your toes on a picture postcard beach, researchers have some good news - the world's sandy shores are increasing.
But while reclaiming land from the sea might be one factor helping boost beaches overall, around 70,000 kms (40,000 miles) of sandy coastlines are being washed away and erosion in marine reserves may point to a bleaker future for beach lovers.
The first global survey of the world's beaches showed 28 percent of beaches are growing and nearly half are stable, said researchers, whose analysis of nearly 2 million satellite images was published in the Scientific Reports journal this week.
"Although globally on average our beaches are accreting, which is good news for holidays and destinations, there are definitely areas that are also eroding," said Arjen Luijendijk, coastal engineer at Delft University of Technology in the Netherlands and one of the authors of the report.
A quarter of the world's beaches are being eroded at a rate of more than half a meter (20 inches) a year, said the researchers, who found beaches make up around 30 percent of the world's coastline.
Some 6,000 kms of beaches are retreating at an even faster rate of 5 meters per year, said Luijendijk, who also works at Deltares, a research institute based in the Netherlands.
Analysis of shoreline changes was essential to help better planning along densely populated coasts, said the researchers, who noted 15 out of 20 megacities are now in coastal zones.
Erosion of sandy coasts in some heavily developed areas was already causing a "coastal squeeze" which was likely to worsen due to the impacts of climate change, they said.
Marine protected areas are also causing "serious concern", said the report, with the majority of their shorelines are being eroded.
Projects to maintain and protect coastal areas in countries such as the Netherlands or reclaim land in Dubai, China and Singapore, have contributed to a 3,660 sq kms increase in the world's beaches over the past three decades.
In Namibia, some beaches were growing at rate of 8 meters per year after diamond miners built undersea embankments, said the researchers.
Some beach areas are also growing naturally, with rivers in China taking sand to the coast, and huge dunes migrating towards the sea in Mauritania and Madagascar.
However, the United States is home to four of the seven fastest eroding beaches, with some coastal areas in Texas and Louisiana receding by up to 15 meters a year, with Mississippi river damming affecting the amount of sand reaching the coast.
"The main question for the future is whether there will be enough sand available to maintain all beaches," said a statement from Deltares on the report.
Reporting by Sophie Hares; Editing by Astrid Zweynert @azweynert.
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