Rivers across the United States are experiencing increasing temperatures.
A recent analysis of nearly 1,500 river locations spanning over 40 years reveals a rise in the frequency, intensity, and duration of heat waves, posing risks to many species accustomed to cooler waters.
“The increase in river heat waves is actually outpacing that of air heat waves, which is quite surprising,” states Li Li, a professor of environmental engineering at Pennsylvania State University and the study’s author.
A new analysis published in the peer-reviewed journal Proceedings of the National Academy of Sciences is the first comprehensive study defining river heat waves as five consecutive hot days compared to seasonal averages.
The researchers identified climate change, which significantly impacts humans, as a major contributor to this trend, due to diminishing snowpacks and slower stream flows.
Human factors also play a role; for example, dams inhibit downstream flow, while urban structures absorb heat, warming both air and water.
Scientists are concerned that species reliant on cold water, such as salmon and trout, will increasingly struggle as river temperatures rise. Li emphasizes the necessity of tracking fish fatalities and ongoing trends.
Higher temperatures decrease the amount of dissolved oxygen in water. Additionally, cold water species generally exhibit increased metabolism in warmer conditions, leading to further oxygen depletion.
These findings could influence basin management strategies and help determine if adjustments in irrigation or dam releases can support aquatic life during elevated temperatures.
“Water management practices can significantly impact heat waves,” noted Jonathan Walter, a research scientist at UC Davis’ Center for Watershed Sciences, who was not part of the study. “If there is sufficient reservoir water, it may be feasible to moderate downstream temperatures by releasing water to mitigate extreme heat.”
While heat waves in oceans and lakes have been studied extensively, there has been limited research on the implications of rising temperatures in rivers until now.
Satellite data have advanced the study of ocean and lake heat, but river temperature research is challenged by reliance on often unusable river gauge sensors, resulting in significant data gaps.
For this new study, researchers analyzed data from 1,471 US Geological Survey monitoring sites from 1980 to 2022.
This data enabled an assessment of shifts in streams nationwide, revealing that by 2022, river heat waves were occurring more frequently than in 1980, with an average increase of 1.8 additional heatwave events per year. These heat waves were also more severe, with temperatures during these events being approximately 0.8 degrees Fahrenheit higher in 2022 than in 1980. Moreover, the duration of heat wave events extended by over three days.
Li noted that this extra heat caused an average of about 12 days of heat stress for cold water species. The study defined 59°F as the threshold for heat stress, as many species, including bull trout, face survival challenges at this temperature.
“When considering water, its visibility draws attention to its significance,” Li remarked. “We hope this research raises public awareness on water quality challenges stemming from climate change.”
Source: www.nbcnews.com
