TEPIC (Mexico) • 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 70,000km 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 beaches showed 28 per cent of beaches are growing and nearly half are stable, said researchers, whose analysis of nearly two million satellite images was published in the Scientific Reports journal last 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 Mr Arjen Luijendijk, a 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 metre a year, said the researchers, who also found that beaches make up around 30 per cent of the world's coastline.
Some 6,000km of beaches are retreating at an even faster rate of 5m per year, said Mr Luijendijk, who also works at Deltares, a research institute based in the Netherlands.
Analysis of shoreline changes was essential to help with better planning along densely populated coasts, said the researchers, who noted that 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, the report said.
Marine protected areas are also causing "serious concern", said the report, with the majority of their shorelines 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 km increase in the world's beaches over the past three decades.
In Namibia, some beaches were growing at rate of 8m 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 15m a year, with the damming of the Mississippi River 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.