Skagit River Basin Climate Science Report Lead Authors: Se-Yeun Lee 1,3 Alan F. Hamlet 2,3,4 1 Post-doctoral Research Assistant, Civil and Environmental Engineering, University of Washington 2 Research Assistant Professor, Civil and Environmental Engineering, University of Washington 3 Climate Impacts Group, University of Washington 4 Skagit Climate Science Consortium September, 2011 Report Citation: Lee, Se-Yeun, A.F. Hamlet, 2011: Skagit River Basin Climate Science Report, a summary report prepared for Skagit County and the Envision Skagit Project by the Department of Civil and Environmental Engineering and The Climate Impacts Group at the University of Washington. Temporary Report URL: http://ftp.hydro.washington.edu/pub/hamleaf/skagit_report/final/ Acknowledgments: The project has been funded wholly or in part by the United States Environmental Protection Agency under assistance agreement WS-96082901 and PO-00J08201 to Skagit County. The contents of this document do not necessarily reflect the views and policies of the Environmental Protection Agency, nor does mention of trade names or commercial products constitute endorsement or recommendation for use. Thanks to John Lombard (Lombard Consulting, LCC), who provided an early review of Chapter 1 of the report and made a number of important contributions to this chapter, particularly on the history of development in the Skagit basin. Thanks to Rob Norheim at the Climate Impacts Group for GIS support and figures, and to Lara Whitely Binder at the Climate Impacts Group for early internal review of the document. The authors are also indebted to the report’s technical reviewers, whose thorough evaluation, constructive criticism, and many useful suggestions greatly improved the manuscript: Ch1: Ed Knight (Swinomish Tribe), Dr. Eric Grossman (USGS) Ch 2,3: Karin Bumbaco (WA State Climatologist’s Office) Ch 4: Dr. Jon Riedel (N. Cascades National Park) Ch 5: Dr. Marijke Van Heeswijk (USGS) Ch 6; Dr. Eric Grossman (USGS) Ch 7: Dr. Greg Hood (Skagit River System Cooperative) Ch 8: Ron Tressler (Seattle City Light) Table of Contents 1. Skagit Basin Overview ....................................................................................................... 1 1.1 Overview of the Skagit River Basin ............................................................................. 1 1.2 Geology and Land Cover .............................................................................................. 2 1.2.1 Geology .................................................................................................................. 2 1.2.2 Land Cover ............................................................................................................. 4 1.3 Human Settlement of the Skagit Basin ......................................................................... 6 1.3.1 Drainage Infrastructure .......................................................................................... 7 1.3.2 Dams....................................................................................................................... 9 1.3.3 Highways .............................................................................................................. 10 1.4 Ecological Change ...................................................................................................... 10 1.5 Population Growth and Future Projections ................................................................. 13 1.6 Summary and Conclusions ......................................................................................... 14 1.7 References ................................................................................................................... 16 2. Climate Variability ........................................................................................................... 21 2.1 Overview of Historical Variations in Pacific Northwest Climate .............................. 21 2.2 Global Climate Patterns Affecting Pacific Northwest Climate .................................. 24 2.2.1 The El Niño-Southern Oscillation ........................................................................ 24 2.2.2 The Pacific Decadal Oscillation (PDO) ............................................................... 26 2.3 Impacts of ENSO and the PDO on Pacific Northwest Climate and Hydrology ......... 27 2.3.1 PNW Temperature and Precipitation ................................................................... 28 2.3.2 Effects of the PDO and ENSO on PNW Hydrology ............................................ 29 2.4 ENSO and PDO Impacts on the Skagit River Basin‟s Climate and Hydrology ......... 33 2.4.1 Skagit Basin Temperature and Precipitation ........................................................ 33 2.4.2 Skagit Basin Snowpack ........................................................................................ 34 2.4.3 Skagit Basin Streamflow ...................................................................................... 35 2.4.4 Skagit Basin Flood Risk ....................................................................................... 40 2.4.5 Skagit Basin Water Temperature ......................................................................... 41 2.4.6 Heating and Cooling Energy Demand ................................................................. 42 2.5 Summary and Conclusions ......................................................................................... 43 2.6 References ................................................................................................................... 45 3. Climate Change Scenarios ................................................................................................ 50 3.1 Global Climate Models ............................................................................................... 51 3.2 Dynamical Downscaling Using Regional Scale Climate Models (RCMs) ................ 54 3.3 Statistical Downscaling Approaches .......................................................................... 55 3.3.1 Delta Method ........................................................................................................ 55 3.3.2 Transient Bias Corrected and Statistical Downscaling (BCSD) Method ............. 56 3.3.3 Hybrid Delta Downscaling Method ..................................................................... 57 3.4 Climate Change Impacts on Meteorological Conditions and Sea Level Rise ............ 57 3.4.1 Changes in Temperature....................................................................................... 57 3.4.2 Changes in Precipitation....................................................................................... 60 3.4.3 Changes in Sea Level ........................................................................................... 63 3.5 Summary and Conclusions ......................................................................................... 67 3.6 References ................................................................................................................... 70 4. Glaciers ............................................................................................................................. 74 4.1 Background ................................................................................................................. 74 4.2 Global glacier changes ................................................................................................ 76 4.3 Glacial changes in the Skagit Basin and North Cascades ........................................... 80 4.3.1 Glaciers monitored by NCGCP ............................................................................ 82 4.3.2 Glaciers monitored by the National Park Service ................................................ 84 4.4 Summary and Conclusions ......................................................................................... 90 4.5 Reference .................................................................................................................... 92 5. Hydrology ......................................................................................................................... 97 5.1 Background ................................................................................................................. 98 5.2 Hydrologic Impacts over the Pacific Northwest ....................................................... 100 5.2.1 Implications of changes in April 1 snow water equivalent ................................ 100 5.2.2 Implications of changes in seasonal streamflow timing..................................... 102 5.3 Hydrologic impacts in the Skagit River basin .......................................................... 105 5.3.2 Changes in mean monthly streamflow ............................................................... 110 5.3.3 Changes in Hydrologic Extremes ....................................................................... 112 5.4 Groundwater ............................................................................................................. 117 5.5 Drainage and Potential Conversion to Marsh in Low-Lying Areas ......................... 118 5.6 Summary and Conclusions ....................................................................................... 118 5.7 References ................................................................................................................. 120 6. Geomorphology .............................................................................................................