WATER AND ENERGY SECTOR VULNERABILITY TO CLIMATE WARMING IN THE SIERRA NEVADA: Simulating the Regulated Rivers of California’s West Slope Sierra Nevada A White Paper from the California Energy Commission’s California Climate Change Center Prepared for: California Energy Commission Prepared by: University of California, Davis JULY 2012 CEC‐500‐2012‐016 David E. Rheinheimer Scott T. Ligare Joshua H. Viers University of California, Davis Davis, California, 95616 USA DISCLAIMER This paper was prepared as the result of work sponsored by the California Energy Commission. It does not necessarily represent the views of the Energy Commission, its employees or the State of California. The Energy Commission, the State of California, its employees, contractors and subcontractors make no warrant, express or implied, and assume no legal liability for the information in this paper; nor does any party represent that the uses of this information will not infringe upon privately owned rights. This paper has not been approved or disapproved by the California Energy Commission nor has the California Energy Commission passed upon the accuracy or adequacy of the information in this paper. ACKNOWLEDGEMENTS This research was made possible by funding from the California Energy Commission. We would like to thank Mike Kiparsky (University of Idaho) for providing computational support, as well as Jack Sieber, Vishal Mehta, and other staff at the Stockholm Environment Institute for providing and supporting WEAP21. We also thank past and present students Shannon Brown, Erik Moreno, and Danielle Salt for their modeling assistance. Finally, we thank the anonymous reviewers of this work for their valuable comments. i ABSTRACT Climate warming is expected to affect the beneficial uses of water in the Sierra Nevada, impacting nearly every resident of California. This paper describes the development and results from an integrated water resource management model encompassing water operations and hydropower generation for the west slope Sierra Nevada spanning the Feather River basin in the north to the Kern River basin in the south at the weekly time step. This model application includes management of reservoirs, run-of-river hydropower plants, water supply demand locations, conveyances, and instream flow requirement. Model validation indicates that most major hydropower turbine flows were simulated well, with wetter years modeled more effectively than drier years. The results of this work indicated that hydropower generation will be reduced by approximately 8 percent with 6°C (10.8°F) warming, consistent with other studies, with a conservative parameterization of no change in precipitation. Reservoir operations adapt to capture earlier and greater runoff volumes that result from earlier and greater runoff due to climate warming. Seasonal compensation in operations is insufficient to overcome warming mediated losses. Keywords: water energy nexus, water management, climate change, non-stationary climate, regulated rivers, reservoirs, habitat, Sierra Nevada Please use the following citation for this paper: Rheinheimer, D. R., S. T. Ligare, and J. H. Viers (Center for Watershed Sciences, University of California, Davis). 2012. Water-Energy Sector Vulnerability to Climate Warming in the Sierra Nevada: Simulating the Regulated Rivers of California’s West Slope Sierra Nevada. California Energy Commission. Publication number: CEC-500-2012-016. ii TABLE OF CONTENTS Acknowledgements ................................................................................................................................... i ABSTRACT ............................................................................................................................................... ii TABLE OF CONTENTS ......................................................................................................................... iii LIST OF FIGURES .................................................................................................................................. iv LIST OF TABLES ...................................................................................................................................... v Section 1: Summary .................................................................................................................................. 1 Section 2: Introduction ............................................................................................................................. 2 Section 3: Background .............................................................................................................................. 3 3.1. Water Resources in the Sierra Nevada ......................................................................................... 3 3.2 Regional Climate Warming ............................................................................................................ 3 3.3 Regional Water Resources Management Models ........................................................................ 3 Section 4: Methods .................................................................................................................................... 6 4.1 Model Scope ...................................................................................................................................... 6 4.2 Infrastructure .................................................................................................................................... 6 4.3 Water Evaluation and Planning System (WEAP) ........................................................................ 8 4.4 Inflow Hydrology ............................................................................................................................ 9 4.5 Universal Parameters .................................................................................................................... 10 4.6 Reservoirs ........................................................................................................................................ 11 Storage Capacity ............................................................................................................................... 11 Initial Storage .................................................................................................................................... 11 Volume-Elevation Curves ............................................................................................................... 11 Reservoir Zone Operations ............................................................................................................. 11 Lake Evaporation ............................................................................................................................. 12 4.7 Hydropower ................................................................................................................................... 12 Water Year Index Method ............................................................................................................... 12 Spill Demand Method ..................................................................................................................... 16 4.8 Water Supply Demand .................................................................................................................. 17 4.9 Instream Flow Requirements ....................................................................................................... 17 4.10 Diversions ..................................................................................................................................... 18 iii 4.11 Priority Setting .............................................................................................................................. 18 4.12 Interbasin Transfers ..................................................................................................................... 19 4.13 Integrating Models and Data Management ............................................................................. 19 4.14 Climate Change Scenarios .......................................................................................................... 20 Section 5: Calibration and Model Assessment .................................................................................. 21 5.1 Hydropower Turbine Flow .......................................................................................................... 22 5.2 Reservoir Storage and Evaporation ............................................................................................. 26 Section 6: Results with Warming ......................................................................................................... 28 6.1 WEAP Runoff Scenarios: Air Temperature Increase ................................................................ 28 6.2 VIC Runoff Scenarios: Downscaled GCM Output .................................................................... 34 Section 7: Limitations ............................................................................................................................. 38 Section 8: Conclusions ........................................................................................................................... 40 References................................................................................................................................................. 41 Appendix A: SIERRA Input Parameters ..........................................................................................