Efforts to prevent flooding in the Yellow River may have exacerbated the situation

An analysis of flooding on the Yellow River in China shows that mud barriers designed to prevent flooding have resulted in more frequent flooding.

Building mud barriers along rivers to prevent flooding could have the opposite effect, an analysis of the Yellow River flood in China suggests.

More extreme and frequent precipitation due to global warming means that river flooding is a growing threat to millions of people around the world. Although there is a large body of research on how climate change affects flood risk, the role of human activity is less clear.

To study this, Shi-Yong Yu of Jiangsu Normal University in China and colleagues analyzed the frequency of flooding on the Yellow River in northern China. This 800 km waterway was the cradle of ancient Chinese civilization between 4100 and 3600 years ago.

The researchers compiled a timeline of floods on the river over the past 12,000 years using historical records and river sediment data. They found that between 12,000 and 7,000 years ago, floods were rare, averaging just four floods every 100 years.

They then compared the flood chronology with the records of human activities such as agriculture and found that floods became more frequent after the expansion of local settlements around 4,000 years ago.

In particular, the analysis showed that the intensity of the floods increased significantly around 1,500 years ago, when people began building mud banks along the river as flood barriers called dams, says Yu.

The researchers found that over the past 1,000 years, floods have occurred 10 times more often than before the birth of ancient Chinese civilization. Their analysis shows that human activities, primarily the use of artificial embankments, have caused about 80 percent of this increase in flooding rates, with the rest due to natural climate changes, Yu says.

Computer modeling of the river shows that coastal mud barriers can lead to more sediment accumulation on the river bed. This raises the river bed and raises the water level, making floods more likely, Yu says.

“The paper highlights the need to study a number of human activities that affect flooding against the backdrop of climate change. This is an important message that we need to take into account today,” says James Best of the University of Illinois at Urbana-Champaign.

Artificial embankments are no longer used to prevent flooding in the Yellow River. According to Yu, since the early 1980s, the Chinese government has introduced a policy of conservation of wild coastal vegetation, which keeps the soil around the river stable. This helps prevent soil ingress and may be a better approach, he says.

But because mud barriers are still the preferred flood prevention strategy in many parts of the world, research suggests that other countries should move away from artificial embankments as well, Yu says. “We can learn from the history of rivers,” he says.