Lake Powell Pipeline Final Study Report 19 Climate Change April 2016 Table of Contents Page Executive Summary ES.1 Introduction ................................................................................................................................ ES-1 Chapter 1 Introduction 1.1 Introduction .................................................................................................................................. 1-1 1.2 Methodology ................................................................................................................................ 1-1 Chapter 2 Colorado River Water Distributions 2.1 Colorado River Compact .............................................................................................................. 2-1 2.2 Interim Guidelines for Lower Basin Shortages ............................................................................ 2-1 2.3 Interim Guidelines EIS Hydrology ............................................................................................... 2-3 Chapter 3 Literature Review 3.1 Introduction .................................................................................................................................. 3-1 3.2 Reclamation Literature Review of Climate Change Studies ........................................................ 3-2 3.3 SECURE Water Act Section 9503 (c) ......................................................................................... 3-6 3.4 Other Climate Change Studies ..................................................................................................... 3-6 3.5 Climate Change and Lake Powell Studies .................................................................................... 3-6 3.6 Paleoclimate Studies ..................................................................................................................... 3-7 Chapter 4 Model Studies of Climate Change Effects 4.1 Colorado River Simulation System (CRSS) ................................................................................. 4-1 4.1.1 Lake Powell Pool Elevation ............................................................................................ 4-1 4.1.2 Lake Powell Releases ...................................................................................................... 4-3 4.1.3 CRSS Model Summary ................................................................................................... 4-4 4.2. Virgin River Climate Change Analysis ........................................................................................ 4-4 Chapter 5 Summary and Conclusions References Cited ..................................................................................................................................................... R-1 Abbreviations & Acronyms ..............................................................................................................................A&A-1 List of Preparers ................................................................................................................................................... LP-1 Lake Powell Pipeline TOC-1 04/30/2016 Final Climate Change Study Report Utah Board of Water Resources Tables Table Number Table Title Page Table ES-1 Projected Changes in Colorado River Basin Runoff or Stream Flow in the Mid 21st Century from Recent Studies ....................................................................................... ES-1 Table 2-1 Interim Shortage Guidelines ......................................................................................................... 2-1 Table 2-2 Interim Guidelines for Operating Lake Powell ............................................................................ 2-2 Table 3-1 Annual Average Temperature, Precipitation, Runoff, Storage and Hydropower Results for the Upper Colorado River Basin ................................................................................ 3-3 Table 3-2 Average Ensemble Changes Relative to Historical 1950 to 2099 Modeled Base Case for the Upper Colorado River Basin ............................................................................................. 3-4 Table 3-3 Water Available for Future Consumptive Use by Colorado ...................................................... 3-11 Figures Figure Number Figure Title Page Figure 3-1 Downscaled Precipitation and Temperature Change Projections in Reclamation’s Upper Colorado Region ........................................................................................................................... 3-2 Figure 3-2 Simulated changes in decade-mean runoff for the Colorado River at Lees Ferry ........................ 3-4 Figure 3-3 Simulated Decade-mean Temperature Throughout the Colorado River Basin ............................ 3-5 Figure 3-4 Simulated Decade-mean Precipitation Throughout the Colorado River Basin ............................ 3-6 Figure 3-5 Simulated Decade-mean April 1st Snowpack Throughout the Colorado River Basin ................. 3-7 Figure 3-6 Modeled 1895 to 2050 Lees Ferry Annual Streamflow ............................................................. 3-10 Figure 3-7 2070 Simulated Average Annual Undepleted Streamflow Volume for Colorado River near Cameo ......................................................................................................................................... 3-12 Figure 3-8 2070 Simulated Average Monthly Streamflow for Colorado River near Cameo ...................... 3-12 Figure 3-9 Historical Supply and Use and Projected Future Colorado River Basin Water Supply and Demand ...................................................................................................................................... 3-14 Figure 3-10 Lees Ferry Reconstruction of Annual Streamflow, 1490 to 1997 .............................................. 3-17 Figure 3-11 Reconstruction of Streamflow for the Colorado River at Lees Ferry, 762 to 2005 .................... 3-18 Figure 3-12 Ten-Year Running Means of Four Lees Ferry Streamflow Reconstructions and the U.S. Bureau of Reclamation Natural (gaged) Flow Record ............................................................... 3-19 Figure 4-1 Lake Powell Pool Elevation, DNF Inflow Hydrology, December ............................................... 4-2 Figure 4-2 Lake Powell Pool Elevation, CC Inflow Hydrology, December .................................................. 4-3 Figure 4-3 Probability of Not Exceeding Minimum Power Pool Elevation in March, DNF Inflow Hydrology ........................................................................................................................ 4-4 Figure 4-4 Probability of Not Exceeding Minimum Power Pool Elevation in March, CC Inflow Hydrology ........................................................................................................................ 4-4 Figure 4-5 Lake Powell Releases by Water Year, DNF Inflow Hydrology ................................................... 4-5 Figure 4-6 Lake Powell Releases by Water Year, DNF Inflow Hydrology ................................................... 4-6 Lake Powell Pipeline TOC-2 04/30/2016 Final Climate Change Study Report Utah Board of Water Resources Executive Summary ES.1 Introduction The Lake Powell Pipeline (LPP) Project is planned to supply water from Lake Powell, located on the Colorado River, to communities in southwest Utah. This document was prepared to further the understanding of climate change and its potential effects on the LPP Project water supply resources and environmental effects. This document supplements the environmental resource studies associated with water resources in addressing the objectives found in Study Plan 19: Water Supply and Climate Change. The climate change analysis includes a literature review of existing scientific studies regarding the effects of potential climate change on the hydrology of the Colorado River and existing studies of the paleo- hydrology of the Colorado River. The Bureau of Reclamation (Reclamation) has conducted numerous hydrologic modeling runs using Reclamation’s long-term planning model, Colorado River Simulation System (CRSS). A review of these model results using the alternate hydrology generated from tree-ring data was also incorporated into this study report. Reclamation published the SECURE Water Act Section 9503(c) – Reclamation Climate Change and Water 2011 report (Reclamation 2011a), which assessed climate change risks and how these risks could affect water operations, hydropower, flood control, and fish and wildlife in the western U.S. It represents the first consistent and coordinated assessment of effects of and risks from climate change on future water supplies across eight major Reclamation river basins, including the Colorado, Rio Grande and Missouri river basins. The SECURE Water Act report was supported by Reclamation’s West Wide Climate Risk Assessments: Bias-Corrected and Spatially Downscaled Surface Water Projections study (Reclamation 2011c), which analyzed changes in hydroclimatic variables, such as precipitation, temperature, snow water equivalent, and streamflow, across major Reclamation river basins. General climate change risks for the Upper Colorado Basin reported in the SECURE Water Act report include the following: basin-average mean annual temperature is projected to increase approximately 4°F by 2060 from baseline 1990 temperatures precipitation is projected to increase slightly in the headwater areas warming trends, rather than precipitation