2017 MONTANA CLIMATE ASSESSMENT Stakeholder driven, science informed montanaclimate.org 2017 MONTANA CLIMATE ASSESSMENT | I Bowman Lake, Glacier National Park. Photograph courtesy of Scott Bischke. ON THE COVER Big Hole Valley. Photograph courtesy of Rick and Susie Graetz, University of Montana. II | SEPTEMBER 2017 2017 MONTANA CLIMATE ASSESSMENT Stakeholder driven, science informed Cathy Whitlock1, Wyatt F. Cross2, Bruce Maxwell3, Nick Silverman4, and Alisa A. Wade5 1 Professor of Earth Sciences, Fellow and former co-Director of the Montana Institute on Ecosystems Montana State University Bozeman, MT 2 Associate Professor of Ecology and Director of the Montana University System Water Center Montana State University Bozeman, MT 3 Professor of Agroecology and Applied Plant Ecology, Department of Land Resources and Environmental Science, and co-Director of the Montana Institute on Ecosystems Montana State University Bozeman, MT 4 Research Associate, Montana Climate Office University of Montana Missoula, MT 5 Research Scientist and Affiliate Faculty member University of Montana Missoula, MT 2017 MONTANA CLIMATE ASSESSMENT | III Jefferson River at Lewis and Clark Caverns State Park. Photograph courtesy of Scott Bischke. This material is based upon work supported in part by the National Science Foundation (NSF) Experimental Program to Stimulate Competitive Research (EPSCoR) Cooperative Agreement #EPS- 1101342. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation. The Montana Climate Assessment is available in digital format at montanaclimate.org. Appendices referenced in the body of this assessment are available at that website. Please cite this publication as: Whitlock C, Cross W, Maxwell B, Silverman N, Wade AA. 2017. 2017 Montana Climate Assessment. Bozeman and Missoula MT: Montana State University and University of Montana, Montana Institute on Ecosystems. 318 p. doi:10.15788/m2ww8w. The editorial team for the 2017 Montana Climate Assessment was composed of Thomas R. Armstrong and Samantha Brooks of the Madison River Group Inc., Anna Tuttle and Cathy Whitlock of the Montana Institute on Ecosystems, and Scott Bischke of MountainWorks Inc. IV | SEPTEMBER 2017 CONTENTS xxiii EXECUTIVE SUMMARY xxiii WHAT IS THE MONTANA CLIMATE ASSESSMENT? xxiv MONTANA’S CLIMATE xxiv Climate basics xxv Montana’s unique features xxv Our analysis xxvi Major findings xxx IMPACTS TO MONTANA’S WATER xxx Water in Montana xxx Our analysis xxxii Major findings xxxiii IMPACTS TO MONTANA’S FORESTS xxxiii Forests in Montana xxxiv Our analysis xxxiv Major findings xxxviii IMPACTS TO MONTANA’S AGRICULTURE xxxviii Agriculture in Montana xxxviii Our analysis xxxviii Major findings xl CONCLUSIONS xli LITERATURE CITED 2017 MONTANA CLIMATE ASSESSMENT | V xlii ACKNOWLEDGMENTS xlvi LIST OF ACRONYMS xlvii FOREWORD 1 01. INTRODUCTION TO THE MONTANA CLIMATE ASSESSMENT Cathy Whitlock 8 LITERATURE CITED 9 02. CLIMATE CHANGE IN MONTANA Nick Silverman, Kelsey Jencso, Paul Herendeen, Alisa Royem, Mike Sweet, and Colin Brust 10 KEY MESSAGES 11 NATURAL AND HUMAN CAUSES OF CLIMATE CHANGE 15 CLIMATE CHANGE ASSESSMENTS 16 MONTANA’S OBSERVED CLIMATE 16 Geography and topography 18 Climate divisions 19 Current climate conditions 1981-2010 36 Teleconnections 40 FUTURE PROJECTIONS 40 Global Climate Modeling 46 Temperature projections 54 Precipitation projections 64 KEY KNOWLEDGE GAPS 64 CONCLUSIONS 67 RECOMMENDED FURTHER READING 67 LITERATURE CITED VI | CONTENTS 71 03. WATER AND CLIMATE CHANGE IN MONTANA Wyatt F. Cross, John LaFave, Alex Leone, Whitney Lonsdale, Alisa Royem, Tom Patton, and Stephanie McGinnis 72 KEY MESSAGES 73 INTRODUCTION 75 Climate change and the water cycle 77 Montana water resources 80 Geographic and temporal setting 85 Future projections 86 Chapter organization 88 SNOWPACK 89 Measuring snowpack 89 Montana’s diverse geography and topography influence patterns of snowpack accumulation and snowmelt 90 Long-term variation in snowpack and the importance of ocean-atmosphere linkages 91 Observed regional trends in snowpack 93 Observed trends in Montana’s snowpack 96 Montana’s snowpack is particularly sensitive to warming 96 Snowpack projections for Montana 98 SNOWMELT AND RUNOFF TIMING 99 Observed regional trends in snowmelt and runoff timing 101 Factors that influence snowmelt and the timing of runoff 103 Model projections for snowmelt and runoff timing 2017 MONTANA CLIMATE ASSESSMENT | VII 106 TOTAL ANNUAL STREAMFLOW 107 Observed trends in total annual streamflow 110 Factors that influence total annual streamflow 112 Annual streamflow projections 114 GROUNDWATER 117 Madison Limestone—an aquifer sensitive to changes in climate 120 Irrigation-supported alluvial aquifers will likely be resilient to climate change 122 Fox Hills–Hell Creek aquifer, impacted by user withdrawals 123 DROUGHT 127 Persistent drought 127 Regional and local factors that influence persistent drought 129 Drought and the dominant role of sea-surface temperatures 130 Likelihood of persistent drought 130 Warm-season drought 131 Observed trends in warm-season drought 131 Factors associated with low summer flows in Montana 139 KEY KNOWLEDGE GAPS 140 CONCLUSIONS 140 RECOMMENDED FURTHER READING 141 LITERATURE CITED VIII | CONTENTS 149 04. FORESTS AND CLIMATE CHANGE IN MONTANA Alisa A. Wade, Ashley P. Ballantyne, Andrew J. Larson, and W. Matt Jolly 150 KEY MESSAGES 151 BACKGROUND 151 Forest ownership, communities, and distribution in Montana 155 Potential climate impacts to forests 160 A note on species-level effects 161 DIRECT EFFECTS OF CLIMATE CHANGE ON FORESTS 164 Establishment and regeneration 164 Growth and productivity 166 Mortality and die-off 166 Species range shifts and forest distribution 170 INDIRECT EFFECTS OF CLIMATE CHANGE ON FORESTS 172 Disturbance resulting from fire 176 Disturbance resulting from pathogens and insects 181 Soil responses, nutrient cycling, and carbon storage 182 ADAPTATION STRATEGIES FOR A CHANGING CLIMATE 185 KEY KNOWLEDGE GAPS 185 CONCLUSIONS 188 RECOMMENDED FURTHER READING 188 LITERATURE CITED 2017 MONTANA CLIMATE ASSESSMENT | IX 197 05. AGRICULTURE AND CLIMATE CHANGE IN MONTANA Bruce Maxwell, Becky Weed, Laura Ippolito, Anton Bekkerman, Madison Boone, Megan Mills-Novoa, David Weaver, Mary Burrows, and Laura Burkle 198 KEY MESSAGES 200 BACKGROUND 203 SUMMARY OF KEY CLIMATE PROJECTIONS FOR MONTANA AGRICULTURE 205 SOURCES OF UNCERTAINTY 208 CLIMATE CHANGE EFFECTS ON COMMODITY CROPS IN MONTANA 208 Shifting ratios of spring and winter wheat 210 Increased corn production 211 Price volatility and the cost of uncertainty in commodity markets 215 Pulse crops 216 Irrigation demand and supply 218 Other large-scale production crops: sugar beets, potatoes, and organic grains 221 CLIMATE CHANGE EFFECTS ON LIVESTOCK 221 Forage and feed 222 Forage quantity and species distribution 223 Empirical data on forage quality 224 Implications for resilience 224 Heat stress 225 CLIMATE CHANGE EFFECTS ON POLLINATORS, DISEASE, PESTS, AND WEEDS 225 Pollinators 227 Crop diseases 228 Insect pests 231 Infectious disease in animals 231 Weeds and invasive plants X | CONTENTS 234 THE FUTURE OF MONTANA AGRICULTURE 236 KEY KNOWLEDGE GAPS 237 NEXT STEPS 237 CONCLUSIONS 238 RECOMMENDED FURTHER READING 239 LITERATURE CITED 245 06. KEY KNOWLEDGE GAPS ADDRESSING CLIMATE CHANGE IN MONTANA Cathy Whitlock, Wyatt F. Cross, Bruce Maxwell, Nick Silverman, and Alisa A. Wade 246 CLIMATE 246 WATER 247 FORESTS 248 AGRICULTURE 251 GLOSSARY 263 LIST OF CONTRIBUTORS 2017 MONTANA CLIMATE ASSESSMENT | XI Fort Benton, Montana. Photograph courtesy of Scott Bischke. FIGURES xxvi Figure I. Montana’s seven climate divisions. xxvii Figure II. Trends in annual average temperature across each climate division (Figure I) in Montana. The divisions are northwestern (NW), southwestern (SW), north central (NC), central (C), south central (SC), northeastern (NE), and southeastern (SE). xxviii Figure III. The projected increase in annual average daily maximum temperature (°F) for each climate division in Montana for the periods 2049-2069 and 2070-2099 for (A) stabilization (RCP4.5) and (B) business-as-usual (RCP8.5) emission scenarios. xxxi Figure IV. The focal rivers for this assessment, including black outlines of the seven climate divisions (see Water chapter), contributing watersheds (red), river gage locations (green), and the Continental Divide (dotted). xxxiii Figure V. Existing forest cover type in Montana (Landfire 2012). Gray boundaries delineate climate divisions (see Figure I). xxxix Figure VI. Factors that drive agricultural decisions in Montana. The size of bubble and arrows qualitatively represents the relative importance of each factor’s influence on agricultural production decisions. 3 Figure 1-1. Global climate projections from the Intergovernmental Panel on Climate Change, showing temperature and precipitation trends for two different future scenarios, as described in the Climate chapter of this assessment (IPCC 2014a). 13 Figure 2-1. Changes in important global atmospheric greenhouse gas concentrations from year 0 to 2005 AD (ppm, ppb = parts per million and parts per billion, respectively) (Forster et al. 2007). 17 Figure 2-2. Montana is the fourth largest state in the nation and provides the headwaters for three major river basins. Two of these, the Columbia and the Missouri, encompass almost 1/3 of the landmass of the conterminous US. The Continental Divide is the line running