Lower streamflows across the West

Jason Leppi is happiest when he's in the backcountry - fishing, hunting, hiking, or skiing.

Which is why he started to notice changes in the rivers and streams he loves to fish so much: sometimes the waterflows were much slower and the water levels much lower than he remembered, and occasionally, entire rivers were closed to fishing in the late summer because of low flows and too-warm stream temperatures.

Jason started to wonder what was causing these changes.  Was it a changing climate, as some people seemed to think, or was this a normal part of historical weather cycles in the Rocky Mountains?

To find answers, Jason decided to study patterns in streamflows and air temperatures from 150 river and stream gauge stations set up by the U.S. Geological Survey across Montana, Idaho, and Wyoming, which led to him joining the Resource Conservation graduate program of the Department of Forest Management at the University of Montana in 2008.

Finding Answers

By 2011, he finally had some answers to his questions: he found that in all three states, 89% of the most pristine streams and rivers (waters that weren't used for irrigation or dammed) had significantly lower streamflows between 1951 and 2008.

At the same time, the air temperature gauges next to these streams and rivers clearly showed a significant increase in air temperatures over the same time period.

The take-home message? Air temperatures across the West have gone up significantly in the last 60 years, while streamflows have gone down.

This long-term trend has Jason worried about the native trout fisheries he cares so much about:  how will they cope with these changes in stream habitat conditions, and what can we do to help?

In 2011, the results of his research were published in the scientific journal Climatic Change as further evidence of the West's changing climate and the resulting impacts of these changes on our streams and rivers.

Jason continues to spend time in the backcountry of Montana, and to learn more about U.S. Geological Survey scientists like Clint Muhlfeld who are actively working to address the effects of our changing climate on native trout fisheries.

Since completing his Master's degree at the University of Montana in 2011, Jason Leppi has joined the Alaska office of The Wilderness Society as a Watershed Ecologist, where he now studies the effects of humans on aquatic ecosystems.  Copies of his 2011 paper on streamflows in the Rocky Mountains are available free of charge to anyone who sends an email request to Anne_Carlson@tws.org