Sea-level rise and river engineering “spell disaster” for many of the world’s river deltas, say scientists.
Half a billion people live in deltas, but the newly published research suggests many of these areas are set to be inundated by rising seas.
Some of the lowest lying, including the Mekong and Mississippi, are particularly vulnerable.
The paper is published in the journal Nature.
Lead researcher Dr Liviu Giosan, from Woods Hole Oceanographic Institution in Massachusetts, said dams and other river engineering had exacerbated the problem by reducing the amount of sediment rivers could carry.
In an article he said was “a call to action before it’s too late”, Dr Giosan said rivers were losing the fight between land and sea.
“Rivers produce sediment by eroding the land, and the sea [washes away] that sediment,” he told BBC News.
A delta is the result of a river producing sediment faster than the sea can remove it, resulting in expanses of fertile, flat land. These are home to some of our most sprawling megacities, including Shanghai, Dhaka and Bangkok.
And where they are left pristine, they are also sites of great biodiversity. One of the world’s better preserved deltas, for example – the Danube – is the most extensive wetland in the European Union and a global biodiversity hotspot.
Although the UK has estuarine areas – where rivers flow into brackish coastal areas that have an open connection to the sea – these do not produce enough sediment or flow out on to large enough flats to build a delta.