Efforts to prevent the Yellow River flooding may have made it worse

Analysis of flooding on the Yellow River in China suggests mud obstacles supposed to forestall flooding have resulted in additional frequent floods

By Carissa Wong

Building mud obstacles alongside rivers to forestall floods could have the other impact, suggests an evaluation of flooding from the Yellow River in China.

More excessive and frequent rainfall as a consequence of international warming means river flooding is a rising risk to tens of millions of individuals worldwide. While there’s a giant physique of analysis on how local weather change impacts flood threat, the position of human actions is much less clear.

To discover this, Shi-Yong Yu at Jiangsu Normal University in China and his colleagues explored the frequency of floods on the Yellow River in northern China. This 800-kilometre-long waterway was the cradle of historic Chinese civilisation between 4100 and 3600 years in the past.

The researchers compiled a timeline of floods on the Yellow River from the previous 12,000 years utilizing historic information and knowledge from river sediments. They discovered that flooding was uncommon between 12,000 and 7000 years in the past, with a median of simply 4 floods occurring each 100 years.

They then in contrast the timeline of floods with information of human actions akin to agriculture, and located that floods grew to become extra frequent following the growth of native human settlements round 4000 years in the past.

In specific, the evaluation revealed that flooding charges considerably elevated round 1500 years in the past, when historic individuals started constructing mud ridges alongside the river as flood obstacles, termed levees, says Yu.

Flooding occurred 10 instances extra typically up to now 1000 years in comparison with earlier than the beginning of historic Chinese civilisation, the workforce discovered. Their evaluation suggests human actions, primarily the usage of synthetic embankments, drove about 80 per cent of this improve in flood charges, with the remainder attributable to pure adjustments within the local weather, says Yu.

Computational modelling of the river means that riverside mud obstacles could result in a larger build-up of sediment on the backside of the river. This paradoxically lifts the riverbed and raises water ranges, making floods extra possible, says Yu.

“The work stresses the need to examine the range of human activities affecting flooding in the backdrop of climate change. This is an important message we must take on board today,” says James Best at Illinois University.

Artificial embankments are now not used to stem flooding within the Yellow River, as for the reason that early Eighties, the federal government of China has launched a coverage to preserve wild riverside vegetation, which retains the soil across the river steady, says Yu. This helps stop sediments falling into the river, and could also be a greater method, he says.

But as constructing mud obstacles remains to be the popular flood prevention technique throughout a lot of the world, the analysis means that different nations must also shift away from synthetic embankments, says Yu. “We can learn lessons from studying the history of rivers,” he says.