Climate Change and Water in the West: The Colorado River Basin

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Information about Climate Change and Water in the West: The Colorado River Basin
News & Politics

Published on October 25, 2013

Author: LearnMoreAboutClimate

Source: slideshare.net

Description

First in the University of Colorado Boulder webinar series addressing climate change and its effect on the environment. Guest speakers are Doug Kenney, Ph.D., Director of the Western Water Policy Program at University of Colorado Law School and Jeff Lukas, Senior Research Associate, Western Water Assessment, CIRES, University of Colorado.

Challenges for the Colorado River Basin October 16, 2013 Doug Kenney, Ph.D. Director, Western Water Policy Program University of Colorado Law School Douglas.kenney@colorado.edu Jeff Lukas Senior Research Associate, Western Water Assessment CIRES, University of Colorado Lukas@colorado.edu Organized by: Anne Gold, Ph.D. CIRES and Deb Morrison, CU Boulder School of Education www.learnmoreaboutclimate.org www.cires.colorado.ed u 1

Climate Change & Water in the West Webinar Facilitators Anne Gold, Ph.D. CIRES, Education & Outreach Deb Morrison Ph.D. Candidate CU Boulder, School of Education Kit Seeborg LearnMoreAboutClimate.org Margi Dashevsky CU Boulder 2

Water in the West Webinar Series  Overall Structure ◦ Two webinars ◦ Background reading material on the website  Requirements For Credit  More Webinar Series to come ◦ Extreme Weather in Spring 2014 3

Major rivers of the U.S. 4

Colorado River    1,450 miles long Basin covers 246, 000 sq. mi. Headwaters in high mountains of CO, WY, UT, N M 5

A highly developed (and overworked) river      Covers 7 states and 2 countries (and 22 Indian reservations) Water supply for 40 million people Irrigation water for 5.5 million acres Generates 4,200 megawatts of hydropower Home to 11 National Parks 6

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Nearly all runoff comes from the cool and wet mountain headwaters above 8,000’ Precipitation Runoff mm mm 0” 20” 40” 0” 6” 12” 8

Snowmelt-dominated hydrology: ~80% of annual flow comes April 15July15 Gaged daily flow, Colorado River at Lees Ferry, 19501955 9

Colorado River Compact of 1922 (and the Law of the River) Total Allocation of 16.5 MAF  7.5 MAF to the Lower Basin ◦ ◦ ◦ ◦  4.4 MAF to California 2.8 MAF to Arizona 0.3 MAF to Nevada Doesn’t include LB tributaries   Design of formula requires Upper Basin to release 7.5 MAF downstream each year for the Lower Basin. Allocations to tribes taken out of state allocations where the reservation is located 7.5 MAF to the Upper Basin ◦ 51.75% to Colorado ◦ 23% to Utah 10

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“A river no more” 12

The 1922 Compact assumed more runoff than has been available since then Water Year Flow, MAF Naturalized streamflow, Colorado River at Lees Ferry, 190630 1922 25 20 Assumption: 16-17 million acrefeet on average based on ~20 years of data 15 10 5 0 1900 1910 1920 Data: Reclamation (1906-2010); 2011-13 values estimated from preliminary Reclamation data or projections 13

The 1922 Compact assumed more runoff than has been available since then Naturalized streamflow, Colorado River at Lees Ferry, 1906-2013 Water Year Flow, MAF 30 25 20 15 10 5 Reality: 14.9 million acre-feet on average 0 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010 Data: Reclamation (1906-2010); 2011-13 values estimated from preliminary Reclamation data or projections 14

Tree rings tell us the early 1900s was one of the wettest periods of the last 1200 years 18 Tree-ring reconstruction of Colorado River at Lees Ferry streamflow from 762-2005, with 20-year running mean Annual Flow, MAF 17 16 15 14 13 12 Gage d period 11 10 750 1000 1250 1500 1750 2000 Water Year Reference: Meko et al. 2007, Medieval Drought in the Colorado River Basin, Geophysical Research Letters Data: TreeFlow: http://treeflow.info/upco/coloradoleesmeko.html 15

Allocations at 15 versus 16.5 MAF* NV Mexico CO AZ UT CA WY NM Mexican apportionment and delivery to Lower Basin are generally considered the first two priorities on the river 16

No flow to the Colorado River delta in most years since Glen Canyon Dam built (1963) Photo provided by Jennifer Pitt 17

The Colorado River’s endangered native fish   Evolved with warm, muddy water conditions Need off-channel “backwater” habitat for raising young 18

Glen Canyon Dam and Lake Powell 19

Sediment is now trapped behind dams, so downstream water is clear 1963: Glen Canyon Dam built Sediment in Grand Canyon decreases >95% 20

Dams release water from lower levels of reservoir: cold water, less seasonal change Water Temperature, Colorado R. at Lees Ferry, 1960-2000 1973 Lake Powell nearly full 21

Dams cut off the annual peak flows needed to maintain backwater habitat 1963: Glen Canyon Dam built 22

Since 2000, Colorado River flows have been very low overall Naturalized streamflow, Colorado River at Lees Ferry, 1906-2013 Water Year Flow, MAF 30 14.9 million acre-feet long-term average 25 20 15 10 5 12.3 million acre-feet average, 2000-2013 0 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 Data: Reclamation (1906-2010); 2011-13 values estimated from preliminary Reclamation data or projections 2010 23

Causes of low flows since 2000 Main cause: Below-average precipitation – likely natural variability  Contributing: Above-average temperatures – likely due to anthropogenic climate change  Future: Climate models uncertain about precipitation change, but high confidence in further warming 24

Climate models: decreasing flow likely in the Colorado River over the 21st century Annual Runoff, MAF 30 25 Median of 39 climate model runs, midemissions scenario 20 15 10 13.0 million acre-feet average, 2035-2064 5 0 1950 2000 2050 2100 Data: Reclamation (1906-2010); 2011-13 values estimated from preliminary Reclamation data or projections 25

Demands have caught up with supply 25 15 10 5 Total Supply (10-yr running average at Imperial Dam) Total Demand (10-yr running average) 0 1923 1927 1931 1935 1939 1943 1947 1951 1955 1959 1963 1967 1971 1975 1979 1983 1987 1991 1995 1999 2003 2007 Volume (MAF) 20 Year 26

Emergence of the “bathtub rings” 27

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Colorado River Basin Supply and Demand Study Plan of Study Framing of the Study Technical Report(TR) – A Development of Water Supply Scenarios TR – B Development of Water Demand Scenarios Identification of System Reliability Metrics TR – C TR – D TR – E Identification and Characterization of Options Evaluation of System Reliability without Options and Strategies TR – G TR – F Development of Portfolios of Options Characterization of System Vulnerabilities Evaluation of System Reliability with Options and Strategies Summary of Findings and Future Considerations Study Report 29

Basin Study: 4 water supply scenarios, using gaged flows, tree-ring flows, and projected flows 1) Gaged Flows 2) Tree-ring Flows 3) Tree-ring Flows blended with Gaged Less water supply 4) Projected Flows 30

A wealth of possible solutions 31

Uncertainty in future water supply: differences among GCM runs Annual Runoff, MAF 30 25 20 15 10 5 0 1950 2000 2050 2100 32

Uncertainty in future water supply: differences among GCM runs Annual Runoff, MAF 30 25 20 15 Most runs show decreasing flow in 21st century, but some show increasing flow 10 5 0 1950 We know that high variability will continue 2000 2050 2100 33

Less uncertainty about timing of runoff: warming will shift the peak earlier Observed Projected (2011-2060) Source: Reclamation – Basin Study Interim Report No. 1 (2011) 34

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Water withdrawals for electricity production Kenny et al. 2009 37

Planning for an uncertain future 38

Understanding choices and trade-offs 39

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Change is: Ever-present is human and natural systems  A challenge for planning and management  An opportunity to do things differently in the future Annual Runoff, MAF  30 25 20 15 10 5 0 1950 2000 2050 2100 41

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Where to go from here? Website  Webinar facilitators  ◦ climatewebinars@gmail.com  Guest Presenters ◦ Jeff Lukas Lukas@colorado.edu ◦ Doug Kenney Douglas.kenney@colorado.edu  Next webinar November 13, 2013 45

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