Winter is getting less reliable.

In Michigan, for example, many families could’ve gone sledding a few months ago on Halloween but not on Christmas when temperatures reached 60 degrees in some areas.

Changing winters also can have troubling consequences for the health and function of nature’s ecosystems. Increasingly common weather events like rain-on-snow events are reducing snowpack and washing away nutrients from soils to our streams and lakes.

This winter, researchers at the University of Michigan Biological Station in northern Michigan are strengthening their snow science with new technology to track the snowpack at an hourly rate and get a deeper understanding of the complexities of global environmental change.

The lab of Aimée Classen, director of the Biological Station and a professor in the Department of Ecology and Evolutionary Biology, installed a high-frequency snow-depth sensor at the 10,000-acre research and teaching campus along Douglas Lake at the end of November.

“Winters are changing, and those changes will impact forest productivity and aquatic water quality,” Classen said. “We are working on a high-tech scale-up of our ongoing, on-the-ground, manual monitoring so we can explore how winters are changing across Michigan and the Midwest.”

Snow discreetly helps regulate the flow of nutrients throughout the ecosystem by providing an insulating layer—a warm blanket—so the soil and root systems underneath do not freeze very deeply, allowing microorganisms to do their important winter chores that later feed plants in the spring and summer.

For 44 years, scientists at the field station about 20 miles south of the Mackinac Bridge have been manually measuring snow depth and accumulation at 8 a.m. every day as part of long-term daily precipitation data.

Biological Station data show between 1980 and today that total annual snowpack has been shrinking as daily average temperatures have risen. UMBS has now automated and intensified the snow measuring process.

Anyone curious about how much snow is on the ground at UMBS can access the Classen Lab’s live hourly data on the Snowpack Dashboard.

Karin Rand, a researcher in and manager of the Classen Lab who works both in Ann Arbor and Pellston, is using the new instrumentation for critical research that aims to capture the nuances and important patterns that may be masked in annual trends and could better explain the impact that declining snowpack has on ecosystem response.

“Weather can change importantly from morning to noon to night,” Rand said. “This sensor will give us a much higher frequency of snow measurements so we understand how quickly snow can accumulate or deteriorate throughout the day.”

The simple setup uses a low-cost sonic rangefinder to monitor the distance between the bottom of the sensor and the ground beneath it. As snow accumulates, that distance will decrease—giving the snow-depth data.

The sensor is powered by a small solar panel and takes measurements hourly. The sensor node was designed by the Digital Water Lab in the U-M College of Engineering led by Branko Kerkez to monitor river depth in watersheds across the state.

“We are lucky to have them lend us a sensor node for terrestrial application and are excited to understand the trends of changing winter,” Rand said.

A decline in snowpack can have cascading effects because microorganisms that live in the soil are active when there’s a thick blanket of snow on the ground.

“This insulation provides enough warmth for soil microorganisms—microbes—to be active in the soil while most plants have halted their growth for winter,” Rand said. “This gives microbes time to eat with no competition from plants. When spring arrives, microbes have converted all sorts of nutrients in the soil into new forms that can be useful to plants, just in time for plants to start taking them up in the spring and summer.”

If there is no snow or the snow turns to rain, soil microbial activity can slow or stop because the microbes are too cold to operate in frozen soil—”leaving our soils with fewer nutrients come springtime when the plants are ready to take those nutrients up for growth.”

Rand said that as winter rain-on-snow and flooding events increase, nutrients are at risk of getting flooded right out of the soil and washed from forests, meadows and agricultural fields into water systems when stream communities are dormant, getting lost from the terrestrial ecosystem and potentially leading to a decline in plant productivity.

“Winters are changing,” she said. “We know this from changing recreational opportunities like skiing and seeing it with our own eyes in our own backyards. But what we can’t see are the things we really want to capture with this soil ecosystem research.

“What’s happening underground? What do we see plants doing above ground? How is that all relating to each other to create a system that works well or maybe starts to fall apart when we introduce different patterns in weather?”

Mid-latitude locations like Michigan are expected to experience an increasing number of rain-on-snow events as part of global change patterns.

Rand said this may result in changes to snow quality including moisture content, grain size, reflectivity and, of course, depth—therefore impacting the ability of snow to regulate nutrient cycling.

“It’s important for us to understand these changing winter precipitation patterns so we also can understand the cascading effects into the summer growing season,” she said. “We want to understand the patterns of nutrient flow because that’s essential to our whole growing season, thinking about our food supply, thinking about forests, thinking about our natural communities and those ecosystems that plants and trees and all of those things support.”

The new hourly snow-depth data will supplement long-term daily precipitation data at Biological Station.

Every morning, resident biologist Adam Schubel switches out rain collection buckets at the National Atmospheric Deposition Program in the UV-B field as part of a larger project to monitor acid precipitation.

“These precipitation data will be useful for looking at past trends and verifying our incoming high-frequency sensor data,” Rand said.

This is only the beginning. The Classen Lab is aiming to grow a statewide network of sensors like the one at the Biological Station.

“If these sensors work, we hope to deploy them all across the state of Michigan and the Midwest to see how increasing rain-on-snow events and winter flooding are impacting forest and agricultural productivity and water quality,” Classen said.

“Ultimately, we would like to pair this with other sensors that will help automate precipitation measurements, specifically rain events. Monitoring rainfall and snow depth at an hourly scale can help us get a clearer picture of how frequent these events occur at the Biological Station,” Rand said.

“A low-cost monitoring station could then be implemented across the state to create a network of sites to understand changing winters across the Midwest.”

For updates about the new sensor and the corresponding research, visit the Classen Lab’s snowpack website.

Written by Chrissy Billau, U-M Biological Station