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Winter in the Sierra Nevada this year was defined by unusually warm temperatures, bringing storms with increased rainfall and less snow. As climate change continues to affect snowpacks in the Sierra Nevada mountains, researchers at the University of Nevada, Reno are working to answer how change is experienced at different elevations. Adrian Harpold, director of the Nevada Mountain Eco-Hydrology Lab, professor in the Department of Natural Resources & Environmental Science in the University’s College of Agriculture, Biotechnology & Natural Resources, and faculty at the Tahoe Institute for Global Sustainability, is part of the team of mountain ecohydrologists studying the flow of water in the Sierra Nevada.

In an interview with the Hitchcock Project for Visualizing Science, Harpold answers questions to help better understand the effects of elevation-dependent climate change in the mountains.

What is mountain ecohydrology?

Mountain ecohydrology is the study of what happens to water in the mountains, in particular, how vegetation and living things use water. A lot of that water comes from winter snowpacks, so we consider variables including where snow falls, how it melts, how water filters into the ground, how vegetation uses water, and how water flows into streams and rivers and ultimately to our taps.

How does elevation affect mountain climates?

The mountains that we live in around here are at the front lines of climate change. We have relatively low mountains: the tops of them are only 10,000 or 12,000 feet. In a changing climate, we're concerned about more rain, less snow, earlier snowmelt and snow disappearing off the landscape before it's ready to be used by vegetation. We are also investigating how early snowmelt stresses our forests, our reservoirs and the things that we depend on for our nice quality of life here in Reno.

What have been the effects of climate change on mountain ecosystems?

What we see globally is that mountains are warming about 20% faster than the lowlands that surround them. It's difficult to assess exactly what the effects of climate change are on a day-to-day basis, but we can look back 30 years and see really clear trends where snow is coming later in the fall. That's limiting our access to some winter recreation opportunities. When the snow melts earlier in the spring, it is causing our rivers to also rise earlier. It's stressing the vegetation because the vegetation is trying to access that water earlier in the year. Additionally, early melt-off leads to longer, drier summers where we have to sustain our water supplies from early snowmelt all the way into September and October, when we get replenished by typical fall rains. 

What do warmer winters mean for wildfire risk?

We're seeing that warmer winters are leading to drier summers, which are making mountain regions more at risk of wildfire. Wildfires create feedback loops with local water supplies: the moment that surface snowmelt ceases in March, April and May, is often when trees have to start relying on water that's stored in the ground, which is causing stress to trees and vegetation. When vegetation is stressed, it grows less and is a drier fuel, making it more at risk of forest fire.

What are some current projects you are working on in your Nevada Mountain Eco-Hydrology Lab at the University?

In the Lake Tahoe Basin and Sierra Mountain Range, I'm interested in looking at consequences of forest management decisions on the watershed. I've done a couple of projects, one related to a large forest restoration called the Tahoe Central Sierra Initiative, where we projected 100 years into the future and tried to answer questions, including how forestry and wildfire management practices change our reservoirs and our stream flows, and how they impact fire severity. What we have concluded is that there are many potential benefits from managing our forests through fuel reduction practices. Our forests are the largest user of water: these trees use a lot of water throughout the year, and if we reduce their biomass, then more of that water will make it down into our streams and rivers.