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

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

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 tree ring reconstruction for Upper Colorado River basin 20th century Water Year Flow (million acre feet)

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, Million Acre Feet Calendar Year

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

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

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

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

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

McCabe and Wolock, Geophysical Research Letters, 2007

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

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

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

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, McCabe and Wolock, Geophysical Research Letters, 2007

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

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, Risk of failing to meet the delivery obligations of the Colorado Compact during a 100-year period McCabe and Wolock, Geophysical Research Letters, 2007

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, Risk of failing to meet the delivery obligations of the Colorado Compact during a 100-year period McCabe and Wolock, Geophysical Research Letters, 2007

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, Risk of failing to meet the delivery obligations of the Colorado Compact during a 100-year period McCabe and Wolock, Geophysical Research Letters, 2007

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, Risk of failing to meet the delivery obligations of the Colorado Compact during a 100-year period McCabe and Wolock, Geophysical Research Letters, 2007

Is a drier West on the horizon?