1. An Upper Basin Scientific Perspective on the Colorado River water supply in the 21st Century 31st Colorado Water Workshop Panel: Is the Colorado River a Developed Resource? July 28, 2006 Gunnison, CO Brad Udall Director CU-NOAA Western Water Assessment Bradley.Udall@colorado.edu wwa.colorado.edu Bradley.Udall@colorado.edu

2. Overview Western Water Assessment Overview of Upper Colorado Compact Climate Change Studies in the West and Basin Lessons from Paleoclimate Studies The Water – Energy Nexus What Does all this mean?

3. Time for some new thinking…

4. Western Water Assessment one of 8 Similar NOAA Regional Integrated Sciences and Assessments (“RISA”) Programs. http://www.climate.noaa.gov/cpo_pa/risa/

5. One Recent WWA Product Climate Overview Paleoclimate Overview Seasonal Forecasting Accuracy River Forecast Center Methods Climate Change In conjunction with California Department of Water Resources http://watersupplyconditions.water. ca.gov/co_nov05.pdf

6. Covers CO, UT, WY Feature Articles Temperature Past Month Precipitation Past Month US Drought Monitor Reservoir Status Colorado Water Availability Temp Outlook Precipitation Outlooks El Nino Status Thanks to: NOAA, State Engineers, NRCS, WWA New Product – Intermountain West Climate Outlook Available at: Wwa.colorado.edu

7. Upper Basin Compact Allocation -1 Article III –51.75% to Colorado –11.25% to New Mexico –23% to Utah –14% to Wyoming –Plus 50,000 af to AZ –III(b)(3) States Allowed to Exceed Apportionments unless so doing deprives another state of its allocation Article VIII –Creates Upper Colorado River Compact Commission

8. Source: Kuhn, CRWCD

10. How Much Developable UB Water? Conventional Analysis –Depends on Hydrology and Mexican Issue Do UB have a year-in, year-out Mexico delivery requirement or is there a surplus above III(a+b) sometimes considering LB tributaries? What are the ten worst hydrologic years you want to include? –Some Numbers ‘ Noah’s Determination’ = 7.5 maf UB, CO=3.9maf (assumes no Mexico requirement) 1988 Hydrologic Determination = 6 maf, CO=3.1 maf (assumes UB Mexico requirement of 750kaf/yr) T-K 1965 study = 5maf, CO=2.7 maf Unconventional Analysis –There is no ‘one’ number – how often, and how much shortage is acceptable? Source: Kuhn

11. The Changing Climate of Climate Change… “The proper response to uncertainty is insurance, not denial” ~ Anonymous

12. Ancient(?) History – 1997 AWWA Journal

13. Bulletin of American Meterological Society, January 2005

14. Declining Snowpack from 1950 to 1997 in large parts of the West Source: Mote, et al.

15. A Warming West from 1950 to 1997… Source: Mote, et al.

16. Precipitation – Mixed Bag from 1950 to 1997 Source: Mote, et al.

17. Declining Snowpack Summary Widespread Declines in SWE in West during 1950-97 Spatial Consistency, Elevational Dependence, Model Agreement all point to climate as cause. Increases in temperature are consistent with rising ghg and will almost certainly continue. Likely that losses in snowpack will continue and even accelerate with highest losses in milder climates and slowest losses in high peaks of northern Rockies and Southern Sierra. Source: Mote, et al.

18. Easterling, BAMS, 2002

19. WWA and Colorado Climate Center Colorado Temperature Trend Study Klaus Wolter and Nolan Doesken 70 to 110 Year Datasets Possible only in a few limited areas Max, Min, Growing Season Length, Cold Snaps, Heat Waves Preliminary Results: Spring Time Warming Trend ‘Most Dominant and Reliable’ Full Results this Fall

20. Colorado River Climate Change Studies over the Years Revelle and Waggoner, 1983 Gleick, 1988 Nash and Gleick, 1991 Nash and Gleick, 1993 Gleick and Chalecki, 1999 Christensen, 2004

21. Lessons from Studies Consistent agreement that it will get warmer, and likely much warmer than global average increases Earlier snowmelt, increased ET very likely More variability in runoff Precipitation uncertain, but warming appears to trump any precipitation increases Caveat: models are still limited in their ability to reproduce regional climates and these studies are not predictions

22. Man Bites Dog: How Does Water Use Affect Climate? Energy Used to Pump, Pressurize, Treat, Heat Water In California Water Use Consumes –20% of all electricity –30% of all natural gas, –Diesel for 120,000 cars/year Saving Water Saves Lots of Energy Consider: carbon caps likely at least on electric power production Increased Price will reduce demand, other feedbacks possible. California Energy Commission, 2005

23. Inland Empire Utility Agency Energy Intensity (kwh/af) IEUA Website, 2005 400 kwh/af 3200 kwh/af

24. New Lee Ferry Streamflow Reconstruction Woodhouse, Gray, Meko Study WRR Added 40+ gage and tree-ring calibration years relative to Stockton and Jacoby 15.2 maf USBR Average Natural Flows 14.3 to 14.7 maf this reconstruction 13.5 maf S&J 1975 reconstruction One 5-year period worse than 2000-2004, but eight other periods may have been as dry.

25. Lees Ferry Reconstruction, 1536-1997 5-Year Running Mean Assessing the 1999-2004 drought in a multi-century context Source: Woodhouse 8 Periods may be worse than 2000-2004

26. Woodhouse, Meko, Gray New Reconstruction of Lees Ferry Streamflow, 20-year moving average, 1536-1997 Dry periods Lowest 20-yr avg.Lowest 25-yr avg 1573-1592 (1)1622-1646 (1) 1622-1641 (3)1623-1647 (2) 1870-1889 (4)1878-1902 (3) 1953-1972 (35)1953-1977 (28) Pluvial (Wet) periods Highest 20-yr avg.Highest 25-yr avg. 1602-1621 (1)1905-1929 (1) 1601-1620 (2)1906-1930 (2) 1905-1924 (6) 1594-1618 (3) Source: Woodhouse

27. Mixing Paleoclimate and Climate Change Trees are not a forecast – climate drivers in the future are likely to be different from the past But Trees are not worthless… –Variability in the tree-ring record is real, very large, and at least some of the ancient droughts would likely stress current water management practices –Historical record shows much more limited variability –As a planning exercise, using the tree-ring generated streamflows with all their variability should provide valuable insights into system vulnerabilities

28. Concluding Thoughts Many Signs – data & models – point to the possibility of reduced runoff in the basin, even with slightly increased precipitation. Hence, additional development in the Upper Basin may have lower than expected yields if based on historical hydrology Were the past to repeat, there are some extended periods where water managers would be quite challenged – the natural variability in the basin is quite large! Development is ultimately a political question not a scientific one. However given the known decadal variability, “is there more water to develop?” is the wrong question. A better question is “how often and what size shortages are acceptable?”