June 2021 | www.gyclimate.org

GREATER YELLOWSTONECLIMATE ASSESSMENT

Past, Present, and Future Climate Change in Greater Yellowstone Watersheds

This page left to right first row: Cody WY (photo credit: Wikimedia under Creative Commons); rail-to-trail conversion between Ashland and Driggs ID second row: pronghorn statues in Pinedale WY; looking west across a portion of Bozeman MT (photos courtesy of Scott Bischke, except as noted) On the cover map: created by Emily Reed (using ArcGIS® software, copyright ESRI and used herein under license) photo: upper Yellowstone River with Electric Peak in the distance and Gardner MT just visible to the right (courtesy of Scott Bischke)

GREATER YELLOWSTONE CLIMATE ASSESSMENT

Past, Present, and Future Climate Change

in Greater Yellowstone Watersheds

Steven Hostetler 1, Cathy Whitlock 2, Bryan Shuman 3,

David Liefert 4, Charles Wolf Drimal 5, and Scott Bischke 6

1 Co-lead; Research Hydrologist; US Geological Survey Northern Rocky Mountain Science Center, Bozeman MT

2 Co-lead; Regents Professor Emerita of Earth Sciences, Montana Institute on Ecosystems, Montana State University, Bozeman MT

3 Wyoming Excellence Chair in Geology & Geophysics, University of Wyoming, Laramie WY; Director, University of Wyoming-National Park Service Research Center at the AMK Ranch, Grand Teton National Park

4 Water Resources Specialist, Midpeninsula Regional Open Space District, Los Altos CA; PhD graduate, Department of Geology and Geophysics, University of Wyoming, Laramie WY

5 Waters Conservation Coordinator, Greater Yellowstone Coalition, Bozeman MT

6 Science Writer, MountainWorks Inc., Bozeman MT

Land Acknowledgment The lands and waters of the Greater Yellowstone Ecosystem have been home to Indigenous people for over 10,000 years. In the most recent millennium, over a dozen Tribes have considered this region a part of their traditional (ancestral) homelands. This includes, but is not limited to, several Tribes and bands of Shoshone, Apsáalooke/Crow, Arapaho, Cheyenne and Ute Nations, as well as the Bannock, Gros Ventre, Kootenai, Lakota, Lemhi, Little Shell, Nakoda, Nez Perce, Niitsitapi/Blackfeet, Pend d’Oreille, and Salish. We pay respect to them and to other Indigenous peoples with strong cultural, spiritual, and contemporary ties to this land. We are indebted to their stewardship. We recognize and support Indigenous individuals and communities who live here now, and those with cultural and spiritual connections to these Homelands.

Support for this project came from Montana State University, University of Wyoming, US Geological Survey, Greater Yellowstone Coordinating Committee, and Greater Yellowstone Coalition. Scott Bischke of MountainWorks Inc. (www.emountainworks.com) served as the report science editor, print-copy designer, and website developer.

Greater Yellowstone Climate Assessment: Past, Present, and Future Climate Change in Greater Yellowstone Watersheds is available in digital format at www.gyclimate.org. While included in this report, a stand-alone Executive Summary is also available.

Suggested citation Hostetler S, Whitlock C, Shuman B, Liefert D, Drimal C, Bischke S. 2021. Greater Yellowstone climate assessment: past, present, and future climate change in greater Yellowstone watersheds. Bozeman MT: Montana State University, Institute on Ecosystems. 260 p. https://doi.org/10.15788/GYCA2021.

Madison River in spring flood, here at 7-mile bridge in Yellowstone National Park, near West Yellowstone MTPhoto courtesy of Scott Bischke

CONTENTSI EXECUTIVE SUMMARY

II What is the Greater Yellowstone Climate Assessment?III Major FindingsXVI Implications for the RegionXIX Concerns from StakeholdersXX ConclusionsXXII Literature Cited

XXIV ACKNOWLEDGMENTS

XXVII LIST OF ACRONYMS

XXVIII FOREWORDCam Sholly

1 1. INTRODUCTION TO THE GREATER YELLOWSTONE CLIMATE ASSESSMENTCathy Whitlock, Steven Hostetler, and Bryan Shuman

5 The Geography of the Greater Yellowstone Area8 The HUC6 Watersheds in the GYA10 Structure of the Assessment12 Literature Cited

15 2. CLIMATE, CLIMATE VARIABILITY, AND CLIMATE CHANGE IN THE GREATER YELLOWSTONE AREACathy Whitlock, Steven Hostetler, Gregory Pederson, and David Liefert

15 Key Messages16 What is Climate?17 Climate and Water Variables Discussed in the Assessment18 Present Climate20 Past Climate Change31 Causes of Climate Change33 Summary35 Literature Cited

40 3. HISTORICAL CLIMATE AND WATER TRENDS IN THE GREATER YELLOWSTONE AREADavid Liefert, Bryan Shuman, Steven Hostetler, Rob Van Kirk, and Jennifer L. Pierce

40 Key Messages41 Introduction42 Data Sources44 Historical Climate Changes in the GYA62 Historical Hydrological Changes in the GYA71 Summary73 Literature Cited

79 4. BACKGROUND TO CLIMATE PROJECTIONSSteven Hostetler

79 Key Messages79 Introduction80 Climate Scenarios82 Climate Models87 Downscaling Climate Projections90 Climate Projections Used in the Greater Yellowstone Climate Assessment 91 Summary92 Chapter 4 Appendix—A Deeper Look99 Literature Cited

102 5. FUTURE TEMPERATURE PROJECTIONS FOR THE GREATER YELLOWSTONE AREASteven Hostetler and Jay Alder

102 Key Messages102 Details of Temperature Projections103 Seasonal Temperature Changes Over the GYA106 Annual Temperature Trends in the Watersheds108 The Seasonal Cycle of Temperature110 Temperature Extremes in HUC6 Towns120 Summary of Projected Temperature Changes121 Chapter 5 Appendix—A Deeper Look125 Literature Cited

127 6. FUTURE PRECIPITATION PROJECTIONS FOR THE GREATER YELLOWSTONE AREASteven Hostetler and Jay Alder

127 Key Messages127 Introduction128 Annual and Seasonal Precipitation Over the GYA130 Precipitation Over the HUC6 Watersheds132 The Seasonal Cycle of Precipitation135 Summary of Projected Precipitation Changes136 Chapter 6 Appendix—A Deeper Look138 Literature Cited

139 7. FUTURE WATER PROJECTIONS FOR THE GREATER YELLOWSTONE AREA Steven Hostetler and Jay Alder

139 Key Messages141 Introduction141 Snow146 Runoff151 Evapotranspiration and Soil Water158 Summary159 Chapter 7 Appendix—A Deeper Look165 Literature Cited

168 8. VOICES FROM THE GREATER YELLOWSTONE AREA Charles Wolf Drimal, Ryan Cruz, Allison Michalski, and Emily Reed

168 Key Messages169 Introduction171 Stakeholder Concerns174 Impacts to Stakeholders177 Current Information180 Information Needed184 Leaders and Current Work 186 Project Needs190 Policy 193 Summary193 Literature Cited

195 9. CONCLUDING REMARKS Cathy Whitlock, Steven Hostetler, Bryan Shuman, David Liefert, Charles Wolf Drimal, and Scott Bischke

201 Science and Monitoring Needs202 Climate Adaptation and Related Needs203 Literature Cited

204 GLOSSARY

215 BIOGRAPHICAL SKETCHES215 Contributors218 Reviewers

ACKNOWLEDGMENTS

The authors of this report acknowledge the many individuals and organizations who provided input and inspiration for the Assessment. We greatly appreciate your help. We list them alphabetically below, with a special callout to those individuals who completed a technical review of a late draft version of the Assessment.

Jake Bell, Adaptation International, Austin, Tx

L. Whitley Binder, University of Washington Climate Impacts Group, Seattle WA

Bob Crabtree, Chief Scientist, Yellowstone Ecological Research Center, Bozeman, MT

David Diamond, Executive Coordinator, Greater Yellowstone Coordinating Committee, Bozeman, MT

K. Dello, Oregon Climate Change Research Institute, Corvallis OR

John Doyle, Crow Tribal Elder, Director and Principal Investigator, Crow Water Quality Project, Crow Environmental Health Steering Committee, Little Big Horn College, Crow Agency, MT

Watershed restoration work along the Ruby River, MontanaPhoto courtesy of Greater Yellowstone Coalition

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Margaret Eggers, Research Assistant Professor of Environmental Health, Montana State University, Bozeman MT

Scott Hauser, Upper Snake River Tribes Foundation, Boise, ID

Julia Hobson Haggerty, Director, Montana Institute on Ecosystems, Montana State University, Bozeman, MT

Jackie Klancher, Professor of Environmental Health & Director of Alpine Science Institute, Central Wyoming College, Riverton, WY

Meade Krosby, University of Washington Climate Impacts Group, Seattle, WA

JoRee LaFrance, Doctoral Student, University of Arizona, Tucson, AZ

Myra Lefthand, MSW, Member, Crow Environmental Health Steering Committee, Little Big Horn College, Crow Agency, MT

Kristin Legg, Ecologist/Manager, Greater Yellowstone Network, National Park Service, Bozeman, MT

W. Andrew Marcus, Director, Atlas of Yellowstone project, University of Oregon, Eugene, OR

Wes Martel, Eastern Shoshone/Northern Arapaho, Senior Wind River Conservation Associate, Greater Yellowstone Coalition, Fort Washakie, WY

Christine Martin, JS. Program Coordinator and US Department of Agriculture Principal Investigator, Crow Water Quality Project, Crow Environmental Health Steering Committee, Little Big Horn College, Crow Agency, MT

Cary Mock, Professor, University of South Carolina, Columbia, SC

Harriet Morgan, University of Washington Climate Impacts Group, Seattle, WA

Alexander (Sasha) Petersen, Adaptation International, Austin, Tx

Andrew Ray, Aquatic Ecologist, National Park Service, Bozeman, MT

Hillary Robison, Yellowstone Center for Resources, Yellowstone National Park, Mammoth, WY

Ann Rodman, Yellowstone Center for Resources, Yellowstone National Park, Mammoth, WY

David Rupp, Oregon Climate Change Research Institute, Corvallis, OR

Naomi Schadt, former MA student, Montana State University, Bozeman, MT

D. Sharp, Oregon Climate Change Research Institute, Corvallis, OR

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Alethea Steingisser, Atlas of Yellowstone Project, University of Oregon, Eugene OR

Julia Stuble, Wyoming Public Lands and Energy Associate, The Wilderness Society, Jackson WY

David Thoma, Landscape Ecologist, National Park Service, Bozeman, MT

Emery Three Irons, Crow Environmental Health Steering Committee, Little Big Horn College, Crow Agency, MT

Paige Tolleson, Project Manager, Montana Institute on Ecosystems, Montana State University, Bozeman, MT

Michelle Uberuaga, Executive Director, Park County Environmental Council, Livingston, MT

Sara Young, Crow Environmental Health Steering Committee, Little Big Horn College, Crow Agency, MT

The authors also thank the many photographers, named throughout the report, who have kindly allowed us to use their images.

REvIEWERS Stephen Gray, PhD, USGS Director of the Alaska Climate Adaptation Science Center, Fairbanks,

AK

Greg J. McCabe, PhD, Research Scientist and Hydroclimatologist, US Geological Survey, Denver, CO

Tom Olliff, Intermountain Region Chief, Landscape Conservation and Climate Change, National Park Service, Bozeman, MT

Adam Terando, PhD, Research Ecologist, USGS Southeast Climate Adaptation Science Center, Raleigh, NC

xxvI | ACKNOWLEDGMENTS

LIST OF ACRONYMS

AMO — Atlantic Multi-decadal Oscillation

AR5 — refers to the Fifth Assessment Report of the IPCC

BSU — Boise State University

CMIP5 — fifth Coupled Model Intercomparison Project

ENSO — El Niño-Southern Oscillation

GCM — global climate model

GHG — greenhouse gas

GYA — Greater Yellowstone Area

GYC — Greater Yellowstone Coalition

HUC — Hydrologic Unit Code

IPCC — Intergovernmental Panel on Climate Change

MCA — Montana Climate Assessment

MSU — Montana State University

NOAA — National Aeronautic and Atmospheric Administration

NPS — National Park Service

NWS — National Weather Service

PDO — Pacific Decadal Oscillation

PDSI — Palmer Drought Severity Index

RCP — Representative Concentration Pathway

SNOTEL — snow telemetry

SNR — signal-to-noise ratio

SWE — snow water equivalent

USGS — United States Geological Survey

UW — University of Wyoming

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FOREWORD

Cam Sholly

Superintendent, Yellowstone National Park (2018-present), Chair, Greater Yellowstone Coordinating Committee (GYCC) (2020- 2022)

June 2021

Climate change is one of the biggest threats to transboundary conservation efforts within the Greater Yellowstone Area (GYA). The Greater Yellowstone Climate Assessment is an excellent synthesis of the best available science and serves as a basis for discussion and common understanding among agencies, organizations, and the public in finding solutions to climate change at a regional scale.

The report was produced by researchers from the universities in Montana, Wyoming, and Idaho, partnering with scientists from the US Geological Survey and National Park Service. It will be a much-needed source of climate change information for diverse groups in the region, including private landowners, communities, policy makers, natural resource specialists, and non-profit organizations. Its coverage of past, present, and future climate change and water resources in the GYA provides baseline information for future assessments of the climate impacts on fish, wildlife and forests in the region, as well as our social-economic well-being and human health.

Impacts to water and other natural resources in the GYA associated with climate change are often unidirectional and push the bounds of historic trends. Reframing our priorities and future resource goals is one of our biggest challenges. We know from the Assessment, for example, that temperatures in the GYA have increased by 0.35°F/decade since 1950 and are projected to increase at a higher rate in the future. Warmer temperatures have already led to decreased snowpack at elevations ranging from 5000 to 7000 ft, drier conditions conducive to fire, widespread die-offs of mature whitebark pine trees, invasive species outbreaks, and changes in the timing and rate of snowmelt are affecting fish spawning and the health of aquatic systems. Grassland habitats are altering bison migratory patterns, and rising temperatures are affecting food availability for songbirds. Protecting and restoring corridors (passageways that connect habitat patches) and connectivity across landscapes will require strong collaboration with partners and programs—public and private—throughout the GYA and beyond. These partners must share knowledge, ensure the survival of native species, and develop meaningful cross-jurisdictional conservation priorities and tools to address climate change threats across the ecosystem.

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Climate change impacts are not just environmental. Every year, millions of visitors from across the world come to Yellowstone to see the park’s awe-inspiring landscapes and wildlife and spend hundreds of millions in local economies. The communities within the GYA are experiencing rapid growth as people move to the region to enjoy the amenities. Climate impacts throughout the GYA, if not addressed, will directly affect the strength of local and regional economies as resource values and use change across the region.

To mitigate the impacts, Yellowstone National Park and its partners are developing climate response strategies that better incorporate climate data and projections into planning, operations, and program management efforts. We continue to develop new tools to provide realistic assessments of climate vulnerabilities and coordinate actions needed to better understand and respond to these changes.

I recommend the Greater Yellowstone Climate Assessment to you as the current definitive source of how climate change is affecting the GYA. The Assessment makes clear that the scale of climate change impacts far exceeds the ability of any one park, agency, organization, or community to effectively respond as a single entity. Integrated, cooperative adaptation strategies across large geographic areas will lead to more informed, comprehensive, and successful results.

Grand Canyon of the Yellowstone River in Yellowstone National ParkPhoto courtesy of Cathy Whitlock

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