Tuesday, November 01, 2016

River Deltas Face Risk from Straying Cyclones

The growing tendency for cyclones to change their paths means river deltas risk being starved of the vital sediment the storms deliver.
As sea levels rise, deltas like the Mekong’s stand to lose the sediments they need. (Image Credit: Nakhon100 via Wikimedia Commons) Click to Enlarge.

Some of the world’s great river deltas could be at risk, not because of increased cyclone hazard but paradoxically because, as climates change, the track of the cyclones has begun to shift away from them.

And although typhoons, hurricanes and tropical cyclones – three names for one storm phenomenon – bring with them destruction, they also deliver prodigious quantities of water to wash billions of tonnes of silt and sediment downstream to create that marshy, meandering and immensely fertile pattern of rich soil and waterways known as a delta.

Without regular deliveries of sediment, deltas could drown as sea levels rise because of global warming.

British scientists report in the journal Nature that they analyzed two decades of water and sediment concentrations discharged into the Mekong River delta in Vietnam.

Planetary ricebowl
The Mekong is the world’s third largest delta:  it covers 39,000 square kilometers, it is home to 20 million people, and its moist fertile soils help make Vietnam one of the planet’s great rice producers.

But a gradual change in the path of tropical cyclones – reported to be moving northwards at 50kms a decade – means that the burden of suspended sediment in the river declined by more than 50 million tonnes between 1981 and 2005.  Of this decline, 33 million tonnes was due to change in cyclone climatology.

Read more at River Deltas Face Risk from Straying Cyclones

No comments:

Post a Comment