America's Rivers Are Changing, Confusing Fish

America's rivers are changing rapidly due to climate change, and fish are getting confused as a result, a new study has found.

The study, published in the journal Science by scientists at the University of Leeds in the U.K., found that climate change is disrupting the seasonal flows of rivers around the world, which is posing a serious threat to water supply and ecosystems. Rivers and their reservoirs provide water for human use, whether for drinking or agricultural purposes, meaning that changes to their flows can greatly affect everyday life.

To reach these findings, the scientists assessed data from river gauging stations and explicitly looked for impacts driven by climate change. From this data they found that 21 percent of the world's rivers had drastic seasonal changes in water flows and concluded that climate change was playing a huge role in this.

And humans are not the only ones affected. Rivers are home to species that are important to the wider environment. When flows are unpredictable, their habitat is at stake.

"The highs and lows of river flow during the different seasons provide vital cues for the species living in the water," Megan Klaar, an associate professor in the University of Leeds School of Geography and co-author of the research, said in a summary of the findings. "For example, a lot of fish use particular increases in the water as a cue to run to their breeding areas upstream or towards the sea. If they don't have those cues, they won't be able to spawn."

Researchers found that 40 percent of the 119 stations they observed in northern North America showed a "significant decrease in river flow seasonality."

In stations in the contiguous United States, there also appeared to be a decrease in seasonal river flow overall, excluding Florida and the Rocky Mountains.

Central North America had a decrease in seasonal river flow in 18 percent of stations studied. The authors also studied rivers across other regions of the globe, and found the situation very similar.

"Our research shows that rising air temperatures are fundamentally altering the natural patterns of river flow," lead author Hong Wang, a Ph.D. researcher at the University of Leeds and the Southern University of Science and Technology in China, said in a summary of the findings.

"The concerning aspect of this change is the observed weakening of river flow seasonality, and that this is as a direct consequence of historical human-induced emissions. This signals a sustained and considerable diminishment of river flow seasonality if air temperatures continue to rise."

River flows around the world are impacted by humans, whether directly through regulations or policies, or indirectly through climate change.

Studies have already noted that rivers were already suffering from direct human activities, without even looking at climate change effects.

Climate change however, is causing weather patterns around the globe to become unpredictable. That means that seasonal cycles that rivers rely on are drastically changing. For example, during the winter, snowpack accumulates in the world's mountain ranges. Come spring, the snow melts and feeds into the surrounding rivers.

However when the expected seasonal periods of floods and droughts weaken, or become unpredictable, these river flows are in trouble.

For instance, early year snowmelt may end up in oceans rather than rivers, meaning there is less water for human use.

Climate change is also causing more extreme weather patterns. An example of this can be seen in California. The state was in the grips of a severe drought for years, until last year the prolonged dry period was broken by a deluge of intense storms. These storms caused severe flooding and landslides that greatly disrupted local communities.

Experts have said these "whiplash" events could become more commonplace as climate change continues to mess with delicate weather patterns.

The authors of this most recent research are urging the need for faster climate change adaptation. As weather patterns change, freshwater ecosystems must be protected and river flows much be managed differently, they state.

"A lot of concern is based upon what climate change will do in the future but our research signals that it's happening now and that increases in air temperature are driving huge changes in river flow," Professor Joseph Holden, the director of water@leeds—a water research center at Leeds University—who supervised Hong Wang's research, said in a statement.

"We should be very concerned about what the future holds given accelerating climate change and begin to think about mitigation strategies and adaptation planning to alleviate the future weakening of seasonal river flow, particularly in locations such as western Russia, Scandinavia, and Canada."

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