1. Sensitivity of Water Supply in the Colorado River Basin to Warming Greg McCabe U.S. Geological Survey, Denver, Colorado Dave Wolock U.S. Geological Survey, Lawrence, Kansas Greg McCabe U.S. Geological Survey, Denver, Colorado Dave Wolock U.S. Geological Survey, Lawrence, Kansas

2. The Colorado River Basin The Colorado River Basin Source: D. Alles, 2007 Streamgage at Lee’s Ferry

3. Source: Steve Gray, University of Wyoming The 20 th century included the wettest and 3 rd wettest periods in the Upper Colorado River Basin during the past 500 years 1 2 3 tree ring reconstruction for Upper Colorado River basin 20th century Water Year Flow (million acre feet)

4. Increasing water demand is stressing the Colorado River water supply, even during one of the wettest centuries. Source: Glen Canyon Institute, March 2005 Colorado River water supply minus consumptive use and losses, 1906-2004 Million Acre Feet 15 10 5 0 -5 -10 20 Calendar Year 1915 19301975199019451960

5. photos by John Dohrenwend, Southwest Satellite Imaging June 29, 2002 December 23, 2003 Are recent dry conditions in the UCRB anomalous, or more reflective of conditions experienced during previous centuries? Lake Powell

6. Potential natural shift to drier conditions + + Increased water demand + + Continued warming Increased risk of water shortages } } Issues and concerns for the Colorado River Basin

7. Question: What is the sensitivity of water supply to increases in temperature? Potential natural shift to drier conditions + + Increased water demand + + Continued warming Increased risk of water shortages } } Issues and concerns for the Colorado River Basin

8. Water-year flow for the Upper Colorado River Basin for 100-year periods McCabe and Wolock, Geophysical Research Letters, 2007

9. Water-year flow for the Upper Colorado River Basin for 100-year periods

10. McCabe and Wolock, Geophysical Research Letters, 2007

11. Water-year flow for the Upper Colorado River Basin for 100-year periods McCabe and Wolock, Geophysical Research Letters, 2007

12. Water-year flow for the Upper Colorado River Basin for 100-year periods McCabe and Wolock, Geophysical Research Letters, 2007

13. Water-year flow for the Upper Colorado River Basin for 100-year periods McCabe and Wolock, Geophysical Research Letters, 2007

14. Risk of Failure (percent of years) Risk of failing to meet the delivery obligations of the Colorado Compact during a 100-year period range of estimated risk of failure for all 100-year periods, 1490-1998 McCabe and Wolock, Geophysical Research Letters, 2007

15. Risk of Failure (percent of years) 20 th century range of estimated risk of failure for all 100-year periods, 1490-1998 Risk of failing to meet the delivery obligations of the Colorado Compact during a 100-year period McCabe and Wolock, Geophysical Research Letters, 2007

16. Risk of Failure (percent of years) 20 th century 20 th century, T+0.86 o C range of estimated risk of failure for all 100-year periods, 1490-1998 Risk of failing to meet the delivery obligations of the Colorado Compact during a 100-year period McCabe and Wolock, Geophysical Research Letters, 2007

17. Risk of Failure (percent of years) 20 th century 20 th century, T+0.86 o C 20 th century, T+2 o C range of estimated risk of failure for all 100-year periods, 1490-1998 Risk of failing to meet the delivery obligations of the Colorado Compact during a 100-year period McCabe and Wolock, Geophysical Research Letters, 2007

18. Risk of Failure (percent of years) 20 th century 20 th century, T+0.86 o C 20 th century, T+2 o C driest century from tree ring record, T+0.86 o C range of estimated risk of failure for all 100-year periods, 1490-1998 Risk of failing to meet the delivery obligations of the Colorado Compact during a 100-year period McCabe and Wolock, Geophysical Research Letters, 2007

19. Risk of Failure (percent of years) 20 th century 20 th century, T+0.86 o C 20 th century, T+2 o C driest century from tree ring record, T+2 o C driest century from tree ring record, T+0.86 o C range of estimated risk of failure for all 100-year periods, 1490-1998 Risk of failing to meet the delivery obligations of the Colorado Compact during a 100-year period McCabe and Wolock, Geophysical Research Letters, 2007

20. Is a drier West on the horizon?