River water temperatures swing hot to cold: discovery shows value of open-source environmental data

Scientists have unveiled rapid fluctuations in river water temperature across the United States (US) with rivers controlled by dams showing more frequent and volatile thermal changes.

Their research was based on national scale, open data from the US Geological Survey. Such data are an essential scientific resource for understanding environmental variability between different places and over time, especially in a warming and increasingly human-dominated world.

In this research, the authors leveraged 15 years' worth of high-resolution temperature data nationally in the first study of its kind globally.

The research team built on conventional river water temperature research on extreme or average values by analysing how quickly thermal conditions are changing, which dictates whether animals can acclimatise or find safe places to survive.

This research – which has been recently published in Environmental Research – revealed the prevalence of rapid temperature changes, with 6,507 surges (temperature rises) and 4,787 plummets (temperature falls) being identified at 88 of the 102 stations assessed.

One striking finding was that both surges and plummets ranged between nearly freezing temperatures to conditions exceeding 40°C over some geothermal hotspots. The authors went on to describe water temperature changes of over 18°C within a single event, transcending extreme thermal shifts previously described worldwide.

Lead author Dr. James C. White, from the University of Birmingham, commented: “Our findings provide critical insights into the dynamics of rapid water temperature changes in rivers, which will help future studies unravel how different water sources and climate patterns affect the likelihood and characteristics of these events.

"Evidence presented in this research is critical for informing more effective environmental management solutions, such as controlling dam flow releases or planting along riverbanks, which is becoming ever more important in a changing climate."

The scientists reported regional differences in these thermal swings across the US, with rivers in western regions like California and Oregon experiencing fewer surges and plummets overall, which were often confined to droughts and heatwaves.

In stark contrast, these rapid temperature shifts were more commonplace in the Upper Colorado river basin across central-west US, where combinations of high aridity and mountainous snowmelt likely played a part. Frequent surges and plummets also manifested across southeastern regions like Florida and Georgia, with these probably the product of persistent storm events.

Co-author David Hannah, Professor of Hydrology and UNESCO Chair in Water Sciences at the University of Birmingham, commented: “By demonstrating how widespread these river water temperature surges and plummets are using long-term national-scale data, we have highlighted rivers that are particularly prone to rapid temperature fluctuations. This provides a critical step towards being able to pinpoint where and when interventions can be implemented that best mitigate river temperature volatility to safeguard and climate proof vulnerable water courses.”