River systems are threatened by human activity and climate change

Human activities are placing an enormous amount of strain on the world’s largest river systems, according to a new study. Political and economic pursuits, combined with the effects of climate change, threaten the future of rivers along with the livelihood of millions of people.

According to the researchers, everyday actions are impacting rivers much faster than the long-term effects of climate change.

Study co-author Jim Best is a professor of Geology and Geography at the University of Illinois at Urbana-Champaign.

“Climate change is of huge importance in terms of changing flood or drought frequency and intensity,” said Professor Best. “However, there is a range of other stressors affecting big rivers such as damming, sediment mining, pollution, water diversions, groundwater extraction and the introduction of nonnative species – all of which affect rivers on a timescale that has much more immediate consequences.”

The researchers explained that rivers respond to changes in the environment through self-adjusting processes of erosion and sedimentation. These responses make rivers very adaptable. 

However, a growing collection of research shows that rivers are becoming less resilient under the compounding stress of human activity and climate change.

The team reviewed published studies on the drivers of flooding in the Mekong River Delta in Southeast Asia, which supports 18 million people and a vast rice agricultural area. 

The analysis revealed that delta subsidence, or sinking, due to groundwater extraction has now become a major issue because of a lack of sediment. Damming and mining are interfering with the natural downstream sediment flows.

“The scale of the effects of sediment starvation and subsidence in driving increased flood risk is currently far greater than sea-level rise generated by global climate change,” said Professor Best. “But when all of these pressures are combined, there is now a real risk that we could cross a major tipping point in the next 10-20 years.”

The researchers reported that politics also plays a significant role in the health and resiliency of the world’s major river systems. For example, the COVID-19 crisis has relaxed the enforcement of pollution monitoring in the United States, and polluters can currently avoid penalties if they argue that violations are a result of the pandemic.

“We have seen evidence of the effect of these types of political and societal shocks on river systems in the past, too,” said Professor Best. “The stresses from the Gulf War led to increased river pollution in the Tigris-Euphrates River Basin, a situation that was also compounded by upstream damming in Turkey.”

The experts emphasize the urgent need for governance at the local level to the international level to effectively confront these issues.

“There are some things we as scientists can do on the monitoring end of this issue, but it will demand collaboration and trust between nations for it to make a difference,” said Professor Best. 

“We can’t take our eye off the ball – we’ve just got to devote more attention to these more frequent, shorter-timescale stressors. It’s far from being just about climate change.”

The study is published in the journal One Earth.

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By Chrissy Sexton, Earth.com Staff Writer