Tropical storms linked to decline in natural flood barriers
Thursday, October 20, 2016, 3:40 PM - Scientists from the University of Southampton have connected tropical storm patterns to the decline of river deltas -- a naturally occurring landform created from sediment deposits.
Deltas form when the flow of a river reaches a slow-moving or stationary body of water, losing the power to transport sediment. This sediment is then released at the mouth of the river; depending on how much sediment the rivers drop, sometimes the tide can't sweep it all away, causing layers to build and a delta to form.
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Researchers examined Vietnam's Mekong River delta -- the third largest river delta in the world -- and found that varying patterns in the behaviour of cyclones is caused less sediment to run into rivers upstream of the Mekong delta. This, in turn, would deprive the delta of materials essential to protect it from flooding.
Naturally, living on a delta is highly dependent on an adequate and consistent build-up of sediment, so a steady flow of sediment is crucial to prevent the landform from flooding.
"Our study is the first to show the significant role tropical storms play in delivering sediment to large river deltas," said Stephen Darby, the study's lead researcher and professor at the University of Southampton. "We show that although human impacts affect the amount of sediment in a river – cyclonic activity is also a very important contributing factor.”
The Mekong is home to 20 million residents and plays a crucial role in Vietnam's economy through rice production.
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Scientists who worked on the study created a new way to analyze historic measurements of water discharge into the Mekong River, detecting sediment concentration from 1981 to 2005.
They then pinpointed the impact of changes in tropical storms on the sediment load.
"Their data shows that of all the sediment transported to the delta, one third is due to tropical cyclones," the University of Southampton noted in a statement. " It also shows that the Mekong’s sediment load has declined markedly in recent years – largely due to changes in the location and intensity of storms tracking across the upstream rivers that feed the delta.
According to Darby, the results are incredibly important.
"Mekong’s sediment load is already declining as a result of upstream damming and other human impacts such as sand mining," Darby said. "Understanding the role played by changes in tropical cyclone climatology gives us a broader knowledge of the threats facing this delta and others like it around the world."
Roughly 500 million people reside or work on the world's major river deltas -- the most widely known including the India/Bangladesh's Ganges River, China's Yangtze River, and the Mississippi River to the south.
The study's findings were published in the journal Nature.
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SOURCE: University of Southampton