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Thursday, April 27, 2023

Climate change is already impacting stream flows across the US

DRI researchers examined more than 500 watersheds across the country and found that increased winter temperatures are driving more extreme fluctuations in streamflow

Peer-Reviewed Publication

DESERT RESEARCH INSTITUTE

Climate change is here, and scientists continue to discover new ways that the world around us is changing. In a new study published in the May issue of the Journal of Hydrology, DRI researchers show that altered weather patterns are impacting stream flows across the country, with implications for flooding, drought, and ecosystems.

Led by Abhinav Gupta, Ph.D., a Maki postdoctoral fellow at DRI, the research examined how day to day variations in streamflow changed in more than 500 watersheds in the U.S. between 1980 and 2013. They found that increased winter temperatures have driven the changes, with impacts varying due to local climate and amongst snow and rain-dominated watersheds. This information is important, the researchers say, for helping water managers adapt to climate change’s impacts.

“We wanted to understand how climate change has impacted the hydrological balance across the U.S. based on the observed data,” Gupta says. “Once we understand how climate change has impacted stream flows in the recent past, we can figure out what kind of changes we might see in the future.”

Streams receive water from a variety of sources, including fast, direct input from rainfall, and groundwater that gradually seeps through springs and soil. To understand how climate change is altering stream flows over time, the authors needed to differentiate between normal variability, like seasonal changes, and longer-term trends. To do this, they broke down stream inputs into events that occur at different timescales, like hourly and daily (rainfall), vs monthly and annual (groundwater). Then, they looked at trends for each timescale to see how they changed over time.

“Once we understand how these trends are evolving, we can make educated guesses about what exactly is changing in the watershed – whether it is snowmelt, surface runoff, base flow, or one of many other factors,” says Gupta. “Without studying streamflow in this way (what is called streamflow statistical structure) it's not possible to study all of these components together, at once.”

Their results show that snow-dominated watersheds across the country are receiving more precipitation as rain than historically. This means that streams now have more water coming in short bursts from rainstorms, rather than the slow trickle of melting snow. The shift to short-term stream inputs could also be attributed to faster snowmelt rates due to higher temperatures, the authors say.

“In the past, streamflow changed very slowly over time,” Gupta says. “But now, because of climate change, we have faster fluctuations in streamflow, which means that we can have a lot of water in a very small amount of time and then we can have no water for a long period of time. These extreme swings are occurring more and more.”

Although the researchers found increased temperatures and changes in rainfall in all watersheds, differences in local climate dictate how this influences streamflow. In humid locales like Florida and the Pacific Northwest, storm inputs decreased, as higher temperatures caused more evaporation, leading the soil to absorb more rainwater. In the Great Plains and Mississippi Valley, contributions to streams from slow, long-term inputs like groundwater are very low, likely also due to high evaporation rates. Arid watersheds saw an increase in the number of days each year without rainfall over the study period, as well as a significant increase in winter temperatures, making streamflow more sporadic.

The study didn’t examine other variables that could impact how water moves through watersheds, like changes in forest cover that impact the amount of water used by plants, or soil type, which affects how quickly rainfall permeates into groundwater. Because each watershed is unique, with its own recipe of soil type, climate, and forest cover, “we cannot paint everything with the same brush,” Gupta says. “We need different strategies for different watersheds to adapt to changes in climate. Even within the same region, watershed impacts can vary.”

More research is needed, the study authors say, to understand what is driving changes in streamflow. If streams are increasingly dependent on groundwater, this could impact how water managers regulate groundwater pumping for human use. “That’s the kind of thing we need to know moving forward, in terms of how we manage our water resources,” says Sean McKenna, study co-author and Director of Hydrologic Sciences at DRI. “Can we pump more groundwater, or do we need to be more careful because if we do, we could lose streamflow?”

Gupta says that he plans to build on this research. “Based on this study, we have been able to identify watersheds across the U.S. that have changed. Now that we know which watersheds in our dataset have been affected by climate change, we can look at the future changes in those watersheds.”

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More information: Changes in streamflow statistical structure across the United States due to recent climate change is available from the Journal of Hydrology. DOI: https://doi.org/10.1016/j.jhydrol.2023.129474

Study authors include: DRI researchers Abhinav Gupta, Rosemary Carroll, and Sean McKenna

About DRI
The Desert Research Institute (DRI) is a recognized world leader in basic and applied environmental research. Committed to scientific excellence and integrity, DRI faculty, students who work alongside them, and staff have developed scientific knowledge and innovative technologies in research projects around the globe. Since 1959, DRI’s research has advanced scientific knowledge on topics ranging from humans’ impact on the environment to the environment’s impact on humans. DRI’s impactful science and inspiring solutions support Nevada’s diverse economy, provide science-based educational opportunities, and inform policymakers, business leaders, and community members. With campuses in Las Vegas and Reno, DRI serves as the non-profit research arm of the Nevada System of Higher Education. For more information, please visit www.dri.edu.

JOURNAL

Journal of Hydrology

DOI

10.1016/j.jhydrol.2023.129474

METHOD OF RESEARCH

Observational study

ARTICLE TITLE

Changes in streamflow statistical structure across the United States due to recent climate change

Mixing theory, observation to envision warmer world

Peer-Reviewed Publication

MICHIGAN STATE UNIVERSITY

Measure as climate changes — IMAGE: MICHIGAN STATE UNIVERSITY PHD GRAD LAURA TWARDOCHLEB INVESTIGATES THE EFFECTS OF WARMING ON FRESHWATER BIODIVERSITY. view more
CREDIT: PHOEBE ZARNETSKE, MICHIGAN STATE UNIVERSITY

Climate changes are conjuring a whirlwind ride that seems to present some creatures opportunities to thrive. Scientists scripting supercharged scenarios caution the difference between seasonal coping and long-term adaption is vast – and tricky to predict.

Michigan State University biologists have studied damselflies – which resemble dragonflies and are abundant as both predator and prey in wetlands – to understand what happens throughout their lifecycle from nymph to winged insect, along with what they eat when summers grow warmer and longer.

Their work in this week’s Proceedings of the Royal Society B has a twist – combining seasons of observational and experimental work in the field and lab with input from a theoretical ecologist, a mathematician by training with supersized modeling creds.

The results: A more realistic look at what a hot summer can bring to a nearby pond, and new respect for the blinding speed global warming is bringing.

“We are seeing the pace of climate change is much more rapid than organisms have endured in their evolutionary experience,” said co-author Phoebe Zarnetske, an associate professor of integrative biology

PI of the Spatial and Community Ecology (SpaCE) Lab and director, IBEEM. “That rapid pace is going to be even more of an issue with the increase in extreme events like heat waves.”

The work in “Life-history responses to temperature and seasonality mediate ectotherm consumer–resource dynamics under climate warming” finds that inserting the right level of data gleaned from field experiences, specifically the effects of seasonal changes in temperature on consumer lifecycles, creates a more robust predator-prey simulation model. The work differs from the findings of similar models with less biological realism that predicted warming trends would doom predators. They see Michigan damselflies surviving climate warming by shifting into a lifecycle similar to their southern relatives – squeaking out two lifecycles in a season rather than one.

The work developed from first author Laura Twardochleb’s work as a PhD student in Zarnetske’s lab. She had spent time observing damselflies’ one-year lifecycle in Michigan. They emerge as adults from ponds in the spring. They mate, reproduce and the juveniles grow over a year in the pond by eating zooplankton. They make good study subjects, she said, because they thrive both outside and in the laboratory.

Twardochleb, now with the California State Water Resources Control Board, was part of MSU’s Ecology, Evolution, and Behavior Program and as a part of that took a class by Chris Klausmeier, MSU Foundation Professor of Plant Biology and Integrative Biology.

She saw that early models projecting how warming climates would affect ectothermic predators were significantly simpler than the nature she was observing. For one thing, the models didn’t allow for the north’s change of seasons. The models also weren’t keeping track of a predator’s size and growth rate and changes in their lifecycle with warming.

Meanwhile, Klausmeier, a theoretical ecologist, was recognizing the special sauce an experimentalist brings when creating mathematical models that take assumptions about how organisms behave, grow, birth, die.

“I can make up any model I want unconstrained by reality,” Klausmeier said. “But that’s a little dangerous because of course you want something related to the real world. When you join with an experimentalist you can bring not just the experimental results and parameters, but also bring the deep natural history and knowledge to the system to know the key variables and constraints.”

The work, factoring in a warmer, but still seasonal climate shows how the damselflies can grow and breed more quickly. Creating a model that only allowed the virtual damselflies to live a one-year lifecycle in a warmer world, they burned out and died. Extinction was on the horizon.

But allow the bugs the option of bringing two generations into a season, and thriving was a possibility. “A lot of models said [predators] were going to starve,” Twardochleb said. “That’s what’s exciting – that we can make models more realistic.”

Twardochleb said the work is good groundwork to understand how other species will respond to a warmer world, particularly species like mosquitoes which are both nuisances and potentially carry diseases.

Zarnetske added that the continual challenge will be beyond the idea that different species will be adapting to a new world. Climate change is outpacing that kind of evolution in an unprecedented way. And the weather extremes – heat waves, droughts, floods – are a whole variable.

“That’s our next step,” Zarnetske said. “Unpredictability is hard.”

The work was supported by the National Science Foundation, NASA, the MSU Department of Fisheries and Wildlife and Environmental Science and Policy Program, Kellogg Biological Station and the Society for Freshwater Science.

Damselflies are iconic species whose lifecycles reflect changes to a warming world.

CREDIT

Laura Twardochleb, Michigan State University