Colorado River Water Availability Study Colorado Water Workshop Gunnison, Colorado July 21, 2010 CWCB Project Manager Ray Alvarado Consulting Team AECOM AMEC Earth & Environmental Canyon Water Resources Leonard Rice Engineers Stratus Consulting

“How much water from the Colorado River Basin is available to meet Colorado's water needs?“ Phase I Water Availability under current infrastructure, currently perfected water rights, and current levels of consumptive and non-consumptive water demands Phase II Water Availability under projected demands from existing, conditional, and new water rights and for additional consumptive and non-consumptive water demands Objectives 2Colorado River Water Availability Study – Phase I

StateMod StateCU Statistical Models Observed Hydrology Overall Hydrology Approach GCM’s & Hydrology Paleohydrology 3Colorado River Water Availability Study – Phase I

Douglas-fir, south-central CO From NOAA, NOAA treeflow.info Basis for Paleo-Hydrology 4PRELIMINARY RESULTS – UNDER REVIEWColorado River Water Availability Study – Phase I

Re-sequencing – The Motivation 5PRELIMINARY RESULTS – UNDER REVIEWColorado River Water Availability Study – Phase I

Repeat 100x Paleohydrology – Re-sequencing 1950 Years Colorado River Water Availability Study – Phase I

StateMod StateCU Statistical Models Paleohydrology Observed Hydrology GCM’s & Hydrology Overall Hydrology Approach 7Colorado River Water Availability Study – Phase I

Colorado River Basin “Down-Scaled” Projections Revised Basin-Wide Hydrology Result: Altered Stream Flows Earth Emissions Scenarios Global Climate Models Result: Altered Temperature and Precipitation State of Colorado CDSS Modeling Result: Water Availability GCMs and Hydrology 8Colorado River Water Availability Study – Phase I

Climate Effect Actual Climate Adjusted Actual Climate Adjusted } Climate Effect GCM Hydrology Process 9Colorado River Water Availability Study – Phase I

StateMod StateCU Statistical Models Paleohydrology Observed Hydrology GCM’s & Hydrology Overall Hydrology Approach 10Colorado River Water Availability Study – Phase I

11PRELIMINARY RESULTS – UNDER REVIEWColorado River Water Availability Study | Phase I Natural Flow Results

12PRELIMINARY RESULTS – UNDER REVIEWColorado River Water Availability Study | Phase I Natural Flow Results

13PRELIMINARY RESULTS – UNDER REVIEWColorado River Water Availability Study | Phase I Natural Flow Results

14PRELIMINARY RESULTS – UNDER REVIEWColorado River Water Availability Study | Phase I Natural Flow Results

15PRELIMINARY RESULTS – UNDER REVIEWColorado River Water Availability Study | Phase I Natural Flow Results

16PRELIMINARY RESULTS – UNDER REVIEWColorado River Water Availability Study | Phase I Natural Flow Results

17PRELIMINARY RESULTS – UNDER REVIEWColorado River Water Availability Study | Phase I Natural Flow Results

18PRELIMINARY RESULTS – UNDER REVIEWColorado River Water Availability Study – Phase I Natural Flow

19PRELIMINARY RESULTS – UNDER REVIEWColorado River Water Availability Study | Phase I Natural Flow Results

20PRELIMINARY RESULTS – UNDER REVIEWColorado River Water Availability Study | Phase I Natural Flow Results

21PRELIMINARY RESULTS – UNDER REVIEWColorado River Water Availability Study – Phase I

Result Summary – Natural Flow 22PRELIMINARY RESULTS – UNDER REVIEWColorado River Water Availability Study – Phase I Annual flow increases in some possible futures and decreases in others Annual flow generally increases in parts of the Yampa River basin and at higher elevation watersheds Annual flow generally decreases in south-western watersheds and at lower elevations Shifts toward earlier peak runoff Flow decreases in late summer and early fall

Ranking of uncertainties (Wilby & Harris, 2005), largest to smallest: –GCM Projections –Downscaling method –Hydrology model structure –Hydrology model parameters –Emissions scenarios Uncertainties interact, but are not additive. 23PRELIMINARY RESULTS – UNDER REVIEWColorado River Water Availability Study | Phase I Uncertainties—Natural Flow

All projections, Glenwood Springs 24PRELIMINARY RESULTS – UNDER REVIEWColorado River Water Availability Study | Phase I

Ensemble of GCMs, Glenwood Springs 25PRELIMINARY RESULTS – UNDER REVIEWColorado River Water Availability Study | Phase I

Precipitation Time Series, Lees Ferry 26PRELIMINARY RESULTS – UNDER REVIEWColorado River Water Availability Study | Phase I

Temperature Time Series, Lees Ferry 27PRELIMINARY RESULTS – UNDER REVIEWColorado River Water Availability Study | Phase I

Natural Flow Time series at Lees Ferry 28PRELIMINARY RESULTS – UNDER REVIEWColorado River Water Availability Study | Phase I

Phase I demonstrates broad range of impacts to natural flows. –Complexity of modeling atmospheric circulation –Inherent uncertainties in GCM projections Robust results –Increased temperatures –Less snowpack and earlier melt Conclusions 29PRELIMINARY RESULTS – UNDER REVIEWColorado River Water Availability Study – Phase I

30Colorado River Water Availability Study – Phase I POCKET SLIDES

“How much water from the Colorado River Basin is available to meet Colorado's water needs?“ What is a reasonable base of existing uses for Phase I of the CRWAS? How does historical hydrology compare to paleohydrology? What is a reasonable projection for hydrology affected by climate change? How much water is available to Colorado under certain compact assumptions? Objectives 31Colorado River Water Availability Study – Phase I

“How much water from the Colorado River Basin is available to meet Colorado's water needs?“ Update / expand CDSS based on stakeholder input through BRTs Assess water availability using historical hydrology Assess water availability using paleohydrology Assess water availability using climate-adjusted hydrology Compare water availability from historical and climate-adjusted hydrology Estimate water available to Colorado under certain compact assumptions Technical Approach 32Colorado River Water Availability Study – Phase I

~30 public meetings / workshops / peer reviews –CWCB Board –CWCB, DWR, and AG Staff –CWCB Climate Change Technical Advisory Group (CCTAG) –Interbasin Compact Committee (IBCC) and Basin Roundtables (BRTs) –Joint Front Range Climate Change Vulnerability Study Program (JFRCCVS) –Centennial Water & Sanitation District / Metro District of Highlands Ranch –NOAA Regional Integrated Sciences and Assessments Program (RISA) –University of Colorado’s Western Water Assessment Program (WWA) –Northern Colorado Water Conservancy District (Water User Meeting) –Colorado River Water Conservation District (Annual Seminar) –Colorado House-Senate Joint Agriculture Committee –Front Range Water Council –Colorado Water Congress Public Outreach 33Colorado River Water Availability Study – Phase I

Variable Infiltration Capacity (VIC) Hydrology Model Colorado Decision Support System (CDSS) Colorado River Simulation System (CRSS) Hydrologic Determination Mass Balance Analysis Analysis Tools 34Colorado River Water Availability Study – Phase I

Douglas-fir, south-central CO From NOAA, NOAA treeflow.info Paleo Hydrology 2. How does historical hydrology compare to a longer hydrologic trace based on tree ring analysis 35PRELIMINARY RESULTS – UNDER REVIEWColorado River Water Availability Study – Phase I

Paleo Hydrology--Approach Two approaches –Regression Models flow sequences and magnitudes Based on mathematical model relating tree-ring width to flow magnitude –Re-sequencing Models flow sequences Obtains magnitudes from historical record Based on model of “state” transition –E.g. “wet-to-wet”, “dry-to-wet”… 36PRELIMINARY RESULTS – UNDER REVIEWColorado River Water Availability Study – Phase I

Re-sequencing – The Motivation 37PRELIMINARY RESULTS – UNDER REVIEWColorado River Water Availability Study – Phase I

Paleo Hydrology--Results Statistics of Annual Flows –Median 56-year mean was slightly greater than mean flow Paleo record indicates slightly more wet years Statistics of wet spells and drought –Median durations were similar –Median surplus volumes tended lower –Median drought volumes often higher Extreme events are represented in flow data –This is the real benefit from using the paleo record 38PRELIMINARY RESULTS – UNDER REVIEWColorado River Water Availability Study – Phase I

Repeat 100x Re-sequencing Climate Adjusted Hydrology 1950 Years Colorado River Water Availability Study – Phase I

CDSS Model Nodes

CDSS Baseflow Nodes

CDSS Model Nodes with Results in Report Appendix

Forest Change Hydrology 43PRELIMINARY RESULTS – UNDER REVIEWColorado River Water Availability Study – Phase I Forest Change Due to Fire –Localized –Relatively small except for very rare cases. –Occurrence is substantially random over long periods. Forest Change Due to Insect Infestation –Data Availability –Forest Recovery Timeframe –Water Supply Impact Detection Threshold

Forest Change due to Insect Infestation 44PRELIMINARY RESULTS – UNDER REVIEWColorado River Water Availability Study – Phase I Data Availability –Tree and beetle science is changing rapidly –USFS and participating agencies have ongoing studies in North Platte Basin –Re-growth, snow studies, and new hydrologic data

Forest Change due to Insect Infestation 45PRELIMINARY RESULTS – UNDER REVIEWColorado River Water Availability Study – Phase I Forest Recovery Timeframe: –Re-growth begins immediately via immature trees and understory vegetation –ET reduction offset quickly by grass / shrub regrowth –Evaporation reduction offset by tree re-growth (before 2040)

Forest Change due to Insect Infestation 46PRELIMINARY RESULTS – UNDER REVIEWColorado River Water Availability Study – Phase I Water Supply Impact Detection Threshold: –Most flow volume from sub-alpine forest (elevations >8,000 feet) –20%-30% watershed must be cleared before detectable flow change –Stream flow impact from forest disturbance <<< Impacts from climate change

Approach –Used mass-balance analysis at Lee Ferry (2007 Hydrologic Determination) –Simulated full-development water use requests in upper basin –Calculated 10-year cumulative flow at Lee Ferry. –Calculated upper basin consumptive use that could be maintained considering Compact provisions Hydrology adjusted for climate change NM, UT, WY fully developed All Upper Basin storage capacity fully used Colorado Water Availability for Future Consumptive Use 47PRELIMINARY RESULTS – UNDER REVIEWColorado River Water Availability Study – Phase I

48PRELIMINARY RESULTS – UNDER REVIEWColorado River Water Availability Study – Phase I Colorado Water Availability for Future Consumptive Use Applied Upper Basin water use requests used in 2007 Hydrologic Determination: Potential Lee Ferry ObligationUpper Basin Water Use 75 MAF6.76 MAF 82.5 MAF5.98 MAF

Colorado Water Availability for Future Consumptive Use 49PRELIMINARY RESULTS – UNDER REVIEWColorado River Water Availability Study – Phase I 1906 – 2000 (Hydrologic Determination) 1950 – 2005 Study Period Extended Historical Hydrology Climate Impacted Hydrology –Focus on 2040 time frame –Five projections for the time frame

Colorado Water Availability for Future Consumptive Use Phase I Assumptions on Current Consumptive Use Colorado Water Availability for Future Consumptive Use Phase I Assumptions on Current Consumptive Use 50PRELIMINARY RESULTS – UNDER REVIEWColorado River Water Availability Study – Phase I Estimated by StateMod – natural flows and weather –Current irrigated acreage –Current M&I demands –Simulates diversions, crop CU, evaporation –Excludes evaporation from Aspinall Unit and Navajo evaporation chargeable to New Mexico –Excludes exports to New Mexico Estimated CU = 2.6 MAF

2040 vs All 112 projections at Glenwood Springs 51PRELIMINARY RESULTS – UNDER REVIEWColorado River Water Availability Study | Phase I

Questions Why were the 2070 results “discounted” Why is there so little difference between the distributions for 2040 and 2070? 52PRELIMINARY RESULTS – UNDER REVIEWColorado River Water Availability Study | Phase I

2040 vs By Scenario at Glenwood Springs 53PRELIMINARY RESULTS – UNDER REVIEWColorado River Water Availability Study | Phase I

54PRELIMINARY RESULTS – UNDER REVIEWColorado River Water Availability Study | Phase I P-E Analysis, Winter Park

Hydrology impacts between 2040 and PRELIMINARY RESULTS – UNDER REVIEWColorado River Water Availability Study | Phase I Glenwood Springs

Extremes of curve are from one GCM 56PRELIMINARY RESULTS – UNDER REVIEWColorado River Water Availability Study | Phase I

All projections, Glenwood Springs 57PRELIMINARY RESULTS – UNDER REVIEWColorado River Water Availability Study | Phase I

Ensemble of GCMs, Glenwood Springs 58PRELIMINARY RESULTS – UNDER REVIEWColorado River Water Availability Study | Phase I

2040 vs Lees Ferry 59PRELIMINARY RESULTS – UNDER REVIEWColorado River Water Availability Study | Phase I

Time series at Lees Ferry 60PRELIMINARY RESULTS – UNDER REVIEWColorado River Water Availability Study | Phase I

Precipitation Time Series, Lees Ferry 61PRELIMINARY RESULTS – UNDER REVIEWColorado River Water Availability Study | Phase I

Precipitation Time Series, Lees Ferry 62PRELIMINARY RESULTS – UNDER REVIEWColorado River Water Availability Study | Phase I

VIC Hydrology Response 63PRELIMINARY RESULTS – UNDER REVIEWColorado River Water Availability Study | Phase I

Christensen & Lettenmaier 64PRELIMINARY RESULTS – UNDER REVIEWColorado River Water Availability Study | Phase I

Synthesis Report, Christensen & Lettenmaier PRELIMINARY RESULTS – UNDER REVIEW

66PRELIMINARY RESULTS – UNDER REVIEWColorado River Water Availability Study | Phase I Development of Run-to-Run Uncertainty

Variability—How do GCMs Compare to Paleo? PRELIMINARY RESULTS – UNDER REVIEW

Climate Change: Selection of Projections 68PRELIMINARY RESULTS – UNDER REVIEWColorado River Water Availability Study – Phase I Projections selected based on change in Temperature and Precipitation Selected projections intended to represent a region that contains approximately 80% of all projections Temperature Change (F) Precipitation Change (%)

Projections for 2040 and 2070 not very different Climate Change: Range of Projections 69PRELIMINARY RESULTS – UNDER REVIEWColorado River Water Availability Study – Phase I

Climate Change: 2040 Selected Projections 70PRELIMINARY RESULTS – UNDER REVIEWColorado River Water Availability Study – Phase I

Climate Change: 2070 Selected Projections 71PRELIMINARY RESULTS – UNDER REVIEWColorado River Water Availability Study – Phase I

The selected projections for 2040 are representative of both periods Climate Change: 2040 and 2070 Projection Comparison 72PRELIMINARY RESULTS – UNDER REVIEWColorado River Water Availability Study – Phase I