River floods are becoming more likely globally because of climate change, but not in the waterway’s downstream sections where more people live. That’s according to a new study coauthored by a University of Cincinnati researcher.
Assistant Professor in the College of Engineering and Applied Science Dongmei Feng mapped the daily streamflow of 2.9 million rivers. The goal? To determine how their flows have changed over the past several decades.
“Rivers are providing very valuable water resources and functions for both humans and ecosystems,” Feng said. “... That's my motivation [to] start studying rivers.”
Feng says researchers know rivers are changing continuously. But, there’s little tracking of how those changes are happening over time on a global scale.
The study revealed two key shifts.
“Rivers respond to climate change and human regulation differently depending on their hydrological location,” Feng said. “By that, I mean it's either upstream or downstream or in the middle — that matters.”
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Upstream sections of rivers, near where they begin, are experiencing an increased flow of water, according to the researchers' work. They also found that extreme flood events are increasing significantly in these upstream river sections.
Feng says this is dangerous for people living nearby.
“Those human settlements are typically less protected compared to the downstream segments,” Feng said.
However, the more frequent flooding can have ecosystem benefits. Rivers will be able to deliver nutrients and sediment to the flood plain, which keeps the environment fertile.
Downstream, it’s a different story. Further from the source, rivers are seeing less flow.
“I would say it's kind of concerning,” Feng said. “If you look at the global map of population distribution, you will see downstream are the most surrounded by human settlements — a lot more than upstream. So that means a lot more population relies on the downstream rivers for water resources and maybe energy supply, hydropower supply and other purposes.”
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Feng says those global trends aren’t necessarily manifesting locally.
“In the Ohio River, we didn't see [as] significant changes as we identified at the global scale,” Feng said.
Smaller rivers are seeing the most changes in erosion potential, flood frequency, and nutrient dynamics.
She foresees increases in flooding upstream and decreases in flow downstream having impacts in many places.
“These different responses may reshape the distribution of erosion and flooding globally,” Feng said. “They may impact the river’s function in both societal and ecosystem perspective.”