Miljoenen mensen bedreigd door inzakken rivierdelta's

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Miljoenen bedreigd door inzakken rivierdelta's

BOULDER (ANP) - De meeste grote rivierdelta's in de wereld zakken in, waardoor honderden miljoenen mensen het risico lopen te worden overspoeld. Het gaat onder meer om de Egyptische rivier de Nijl, de Franse Rhône, de Chinese Yangtze en de Amerikaanse Coloradorivier, berichtte de BBC maandag.

Het plaatsen van dammen en het omleggen van waterstromen betekent dat veel minder sediment de deltagebieden bereikt. Daarnaast zakt land in deltagebieden langzaam weg door gasboringen en extractie van grondwater. Ongeveer een half miljard mensen woont in de betreffende gebieden, aldus wetenschappers aan de Amerikaanse universiteit van Colorado in Boulder.

Onderzoekers berekenden dat 85 procent van de grote rivierdelta's afgelopen jaren te maken heeft gehad met ernstige overstromingen. ,,Laagliggende rivierdelta's lopen steeds meer risico op overstroming door de eigen rivieren of door stormen vanaf de oceanen'', aldus een van de onderzoekers.

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'Millions at risk' as deltas sink
Most of the world's major river deltas are sinking, increasing the flood risk faced by hundreds of millions of people, scientists report.

Damming and diverting rivers means that much less sediment now reaches many delta areas, while extraction of gas and groundwater also lowers the land.

Rivers affected include the Colorado, Nile, Pearl, Rhone and Yangtze.

About half a billion people live in these regions, the researchers note in the journal Nature Geoscience.

They calculate that 85% of major deltas have seen severe flooding in recent years, and that the area of land vulnerable to flooding will increase by about 50% in the next 40 years as land sinks and climate change causes sea levels to rise.

"We argue that the world's low-lying deltas are increasingly vulnerable to flooding, either from their feeding rivers or from ocean storms," said Albert Kettner from the University of Colorado in Boulder, US.

"This study shows there are a host of human-induced factors that already cause deltas to sink much more rapidly than could be explained by sea level alone."

Most of the at-risk river basins are in the developing countries of Asia, but there are several in developed nations as well, including the Rhone in France and the Po in Italy.

The Po delta sank by 3.7m during the 20th Century, mainly from methane extraction, the researchers say.

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