Climate, Growth and Drought Threat to Colorado River Water Supply

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Climate, Growth and Drought Threat to Colorado
River Water Supply
Balaji Rajagopalan Department of Civil,
Environmental and Architectural Engineering And Co
operative Institute for Research in Environmental
Sciences (CIRES) University of Colorado Boulder,
CO Presentation to KOWACO February 3, 2009
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Collaborators

• Kenneth Nowak - CEAE / CADSWES
• Edith Zagona - CADSWES
• James Prairie - USBR, Boulder
• Ben Harding - AMEC, Boulder
• Marty Hoerling - NOAA
• Joe Barsugli - CIRES/WWA/NOAA
• Brad Udall - CIRES/WWA/NOAA
• Andrea Ray - NOAA

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A Water Resources Management Perspective
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(No Transcript)
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Resources

• http//cadswes.colorado.edu/publications
• (PhD thesis)
• Regonda, 2006
• Prairie, 2006
• Grantz, 2006
• Stochastic Streamflow Simulation
• http//animas.colorado.edu/prairie/
• http//animas.colorado.edu/nowakkc/
• balajir_at_colorado.edu
• jprairie_at_uc.usbr.gov

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Colorado River Basin Overview

• 7 States, 2 Nations
• Upper Basin CO, UT, WY, NM
• Lower Basin AZ, CA, NV
• Fastest Growing Part of the U.S.
• Over 1,450 miles in length
• Basin makes up about 8 of total U.S. lands
• Highly variable Natural Flow which averages 15
  MAF
• 60 MAF of total storage
• 4x Annual Flow
• 50 MAF in Powell Mead
• Irrigates 3.5 million acres
• Serves 30 million people
• Very Complicated Legal Environment
• Denver, Albuquerque, Phoenix, Tucson, Las Vegas,
  Los Angeles, San Diego all use CRB water
• DOI Reclamation Operates Mead/Powell

SourceReclamation
1 acre-foot 325,000 gals, 1 maf 325 109
gals 1 maf 1.23 km3 1.23109 m3

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When Will Lake Mead Go Dry?Barnett Pierce,
Water Resources Research, 2008

• Water Budget Analysis
• One 50 maf reservoir, increasing UB demands (13.5
  in 2008 -gt14.1 Maf/yr in 2030, 15.1 maf /yr
  inflows, current starting contents
• Linear Climate Change Reduction in Flows w/ some
  natural variability
• Results With Linear 20 Reduction in mean flows
  Over 50 years
• 10 Chance Live Storage Gone by 2013
• 50 Chance Live Storage Gone by 2021
• 50 Chance Loss of Power by 2017
• Is that so?

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Colorado River Demand - Supply
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Declining Lakes Mead and Powell
120 Foot drop13 maf lostCurrent 48, 12 maf
5 Years of 10 maf/yr66 of average flowsWorst
drought in historic record
75 Foot Drop (Max 140)10.5 maf lost Current
56, 14.5 maf
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New York Times Sunday Magazine, October 21, 2007
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Dropping Lake Mead
Lake Meads Delta Circa 1999
2004
1999
Source USGS, Reclamation
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Recent conditions in the Colorado River
BasinPaleo Context

• Below normal flows into Lake Powell 2000-2004
• 62, 59, 25, 51, 51, respectively
• 2002 at 25 lowest inflow recorded since
  completion of Glen Canyon Dam

• Some relief in 2005
• 105 of normal inflows
• Not in 2006 !
• 73 of normal inflows
• 2007 at 68 of Normal inflows
• 2008 at 111 of Normal inflows

Colorado River at Lees Ferry, AZ
5 year running average
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observed record
Woodhouse et al. 2006
Stockton and Jacoby, 1976
Hirschboeck and Meko, 2005
Hildalgo et al. 2002
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Past Flow Summary

• Paleo reconstructions indicate
• 20th century one of the most wettest
• Long dry spells are not uncommon
• 20-25 changes in the mean flow
• Significant interannual/interdecadal variability
• Rich variety of wet/dry spell sequences
• All the reconstructions agree greatly on the
  state (wet or dry) information
• How will the future differ?
• More important, What is the water supply risk
  under changing climate?

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Future Climate
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The Fundamental Problem with Climate Change For
Water Management

• All water resource planning based on the idea of
  climate stationarity climate of the future
  will look like the climate of the past.
• Reservoir sizing
• Flood Control Curves
• System Yields
• Water Demands
• Urban Runoff Amounts
• This will be less and less true as we move
  forward.
• Existing Yields now not as certain given both
  supply and demand changes
• New water projects have an additional and new
  element of uncertainty.

Science, February 1, 2008
Stuff and m
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IPCC 2007 AR4 Projections

• Wet get wetter and dry get drier
• Southwest Likely to get drier

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Models Precip and Temp Biases

• Models show consistent errors (biases)
• Western North America is too cold and too wet
• Weather models show biases, too
• Can be corrected

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A Large Number of Studies Point to a Drying
American Southwest

• Milly et al., 2005
• Seager et a.l, 2007
• IPCC WG1, IPCC WG2, 2007
• National Academy Study, 2007
• IPCC Water Report, 2008
• CCSP SAP 4.3, 2008

From 2040 to 2060, anticipated water flows from
rainfall in much of the West are likely to
approach a 20 percent decrease in the average
from 1901 to 1970, and are likely to be much
lower in places like the fast-growing Southwest.
May 28, 2008, New York Times
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Progression of Data and Models in studies about
the influence of climate change on streamflows in
the Colorado River Basin
3.Water Supply Operations Model
1.Climate Change Data Source
2.Flow Generation Technique
General CirculationModel
Temperature Precipitation
Streamflow
OR
Reservoir storage Hydroelectric powerUB Releases
Stuff and m
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Study Climate Change Technique (Scenario/GCM) Flow Generation Technique (Regression equation/Hydrologic model) Runoff Results Operations Model Used results? Notes
Stockton and Boggess, 1979 Scenario Regression Langbein's 1949 US Historical Runoff- Temperature-Precipitation Relationships 2C and -10 Precip -33 reduction in Lees Ferry Flow   Results are for the warmer/drier and warmer/wetter scenarios.
Stockton and Boggess, 1979   Regression Langbein's 1949 US Historical Runoff- Temperature-Precipitation Relationships 2C and -10 Precip -33 reduction in Lees Ferry Flow   Results are for the warmer/drier and warmer/wetter scenarios.
Revelle and Waggoner, 1983 Scenario Regression on Upper Basin Historical Temperature and Precipitation 2C and -10 Precip -40 reduction in Lee Ferry Flow   2C only -29 runoff,
Revelle and Waggoner, 1983   Regression on Upper Basin Historical Temperature and Precipitation 2C and -10 Precip -40 reduction in Lee Ferry Flow   -10 Precip only -11 runoff.
Nash and Gleick, 1991 and 1993 Scenario and GCM NWSRFS Hydrology model runoff derived from 5 temperature precipitation Scenarios and 3 GCMs using doubled CO2 equilibrium runs. 2C and -10 Precip -20 reduction in Lee Ferry Flow Used USBR CRSS Model for operations impacts. Many runoff results from different scenarios and sub-basins ranging from decreases of 33 to increases of 19.
Christensen et al., 2004 GCM UW VIC Hydrology model runoff derived from temperature precipitation from NCAR GCM using Business as Usual Emissions. 2C and -3 Precip at 2100 -17 reduction in total basin runoff Created and used operations model, CRMM. Used single GCM known not to be very temperature sensitive to CO2 increases.
Hoerling and Eischeid, 2006 GCM Regression on PDSI developed from 18 AR4 GCMs and 42 runs using Business as Usual Emissions. 2.8C and 0 Precip at 2035-2060 -45 reduction in Lee Fee Flow    
Christensen and Lettenmaier, 2006 GCM UW VIC Hydrology Model runoff using temperature precipitation from 11 AR4 GCMs with 2 emissions scenarios. 4.4C and -2 Precip at 2070-2099 -11 reduction in total basin runoff Also used CRMM operations model. Other results available, increased winter precipitation buffers reduction in runoff.
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Precipitation, Temperatures and Runoff in
2070-2099
CRB Runoff From CL
115
Triangle size proportional to runoff changes Up
Increase Down Decrease Green
2010-2039 Blue 2040-2069 Red 2070-2099
-40 to 30 Runoff changes in 2070-2099
80
2C to 6 C
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Colorado River Climate Change Studies over the
Years

• Early Studies Scenarios, About 1980
• Stockton and Boggess, 1979
• Revelle and Waggoner, 1983
• Mid Studies, First Global Climate Model Use,
  1990s
• Nash and Gleick, 1991, 1993
• McCabe and Wolock, 1999 (NAST)
• IPCC, 2001
• More Recent Studies, Since 2004
• Milly et al.,2005, Global Patterns of trends in
  runoff
• Christensen and Lettenmaier, 2004, 2006
• Hoerling and Eischeid, 2006, Past Peak Water?
• Seager et al, 2007, Imminent Transition to more
  arid climate state..
• IPCC, 2007 (Regional Assessments)
• Barnett and Pierce, 2008, When will Lake Mead Go
  Dry?
• National Research Council Colorado River Report,
  2007

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• Almost all the water is generated from a small
  region of the basin at very
• high altitude
• GCM projections for the high altitude regions are
  uncertain

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Future Flow Summary

• Future projections of Climate/Hydrology in the
  basin based on current knowledge suggest
• Increase in temperature with less uncertainty
• Decrease in streamflow with large uncertainty
• Uncertain about the summer rainfall (which forms
  a reasonable amount of flow)
• Unreliable on the sequence of wet/dry (which is
  key for system risk/reliability)
• The best information that can be used is the
  projected mean flow

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Water Supply System Risk Estimation
Streamflow Scenarios Conditioned on climate
change projections
Water Supply Model Management Demand growth
alternatives
System Risk Estimates For each year
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• Streamflow Simulation
• Paleo
• Observations
• Need to Combine

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Need to Combine Paleo and Observed flows for
stochastic simulation

• Colorado River System has enormous storage of
  approx 60MAF 4 times the average annual flow -
  consequently,
• wet and dry sequences are crucial for system
  risk/reliability assessment
• Streamflow generation tool that can generate flow
  scenarios in the basin that are realistic in
• wet and dry spell sequences
• Magnitude
• Paleo reconstructions are
• Good at providing state (wet or dry)
  information
• Poor with the magnitude information
• Observations are reliable with the magnitude
• Need for combining all the available information
• Observed Annual average flow (15MAF) is used to
  define wet/dry state.

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Proposed Framework Prairie et al. (2008, WRR)
Nonhomogeneous Markov Chain Model on the observed
Paleo data
Natural Climate Variability
10000 Simulations Each 50-year long 2008-2057
Superimpose Climate Change trend (10 and 20)
Climate Change
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Source Rajagopalan et al., 1996
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Nonhomogenous Markov model with Kernel smoothing
(Rajagopalan et al., 1996)

• Transition Probability (TP) for each year are
  obtained
• using a discrete Kernel Estimator
• h determined with LSCV
• 2 state, lag 1 model was chosen
• wet (1) if flow above annual median of observed
  record dry (0) otherwise.
• AIC used for order selection (order 1 chosen)

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Transition Probabilities
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Simulation

• Re-sample a block of years (as desired for
  planning say 50 year)
• Using the TP for each year generate a state
  (St)
• Conditionally Re-sample a streamflow magnitude
  from the observed flow
• Identify K-nearest neighbors from the
  observations to the feature vector (St , St-1
  and xt )
• Re-sample one of the neighbor i.e., one of the
  years, say year j
• Flow of year j1 is the simulated flow, Xt1

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Drought and Surplus Statistics
Surplus Length
Surplus volume
flow
Drought Length
Threshold (e.g., median)
time
Drought Deficit
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Drought/Surplus Statistics
K-NN-1 bootstrap Of observed flow
Paleo Obs
Red ? Paleo stat Blue ? Observed stat
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Storage Statistics
60
37

• System Risk
• Streamflow Simulation
• System Water Balance Model
• Management Alternatives
• (Reservoir Operation Demand Growth)

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• Lees Ferry, AZ gauge
• Demarcates Upper and Lower Basin
• 90 of the entire basin flow passes through this
  gauge
• Well maintained gauge
• Annual Average flow is about 15MaF
• Sizeable flow occurs between Lake Powell and Mead
  750KaF/year
• Small but useful flow below Mead also comes in to
  the system
• 250KaF/year

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Water Balance Model

• Storage in any year is computed as
• Storage Previous Storage Inflow - ET- Demand
• Upper and Lower Colorado Basin demand 13.5
  MAF/yr
• Total Active Storage in the system 60 MAF
  reservoir
• Initial storage of 30 MAF (i.e., current
  reservoir content)
• Inflow values are natural flows at Lees Ferry,
  AZ Intervening flows between Powell and Mead
  and below Mead
• ET computed using Lake Area Lake volume
  relationship and an average ET coefficient of
  0.436
• Transmission Losses 6 of Releases

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Combined Area-volume RelationshipET Calculation
ET coefficients/month (Max and Min) 0.5 and 0.16
at Powell 0.85 and 0.33 at Mead Average ET
coefficient 0.436 ET Area Average
coefficient 12
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Management and Demand Growth Combinations

• A. The interim EIS operational policies employed
  with demand growing based on the upper basin
  depletion schedule.
• B with the demand fixed at the 2008 level
  13.5MaF
• C. Same as A but with larger delivery shortages
• D. Same as C but with a 50 reduced upper basin
  depletion schedule.
• E. Same as A with full initial storage.
• F. Same as A but post 2026 policy that
  establishes new shortage action thresholds and
  volumes.
• G. Demand fixed at 2008 level and post 2026 new
  shortage action.
• All the reservoir operation policies take effect
  from 2026

INTERIM EIS INTERIM EIS INTERIM PLUS INTERIM PLUS NEW THRESHOLD NEW THRESHOLD
Res. Storage () Shortage (kaf) Res. Storage () Shortage ( of current demand) Res. Storage () Shortage ( of current demand)
36 333 36 5 50 5
30 417 30 6 40 6
23 500 23 7 30 7
20 8
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Flow and Demand Trendsapplied to the simulations
Blue mean flow trend 15MAF 12MAF By
2057 -0.06MAF/year Under 20 - reduction
Red demand trend 13.5MAF 14.1MAF by 2030
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Flow trend with sample simulation
37.2 of simulations gt 15MAF 22.3 of simulations
gt 17MAF
34.7 of simulations gt 15MAF 18.8 of simulations
gt 17MAF
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PDF of generated streamflows (boxplots) PDF of
observed flow (red)
AR-1
NHMM
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Natural Climate Variability
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Climate Change 20 reduction
Climate Change 10 reduction
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When Will Lake Mead Go Dry?Water Resources
Research, 2008

• Water Budget Analysis
• One 50 maf reservoir, increasing UB demands (13.5
  in 2008 -gt14.1 maf/yr in 2030, 15.1 maf /yr
  inflows, current starting contents
• Linear Climate Change Reduction in Flows w/ some
  natural variability
• Results With Linear 20 Reduction in mean flows
  Over 50 years
• 10 Chance Live Storage Gone by 2013
• 50 Chance Live Storage Gone by 2021
• 50 Chance Loss of Power by 2017
• Problems
• 1.7 maf/year fixed evaporation plus bank storage
• Missing 850 kaf/yr inflows
• Forgotten / Ignored Issues
• System is on a knife-edge, even with existing
  flows
• Normal climate variability can push us over the
  edge without climate change

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Probability of at least one drying Barnett and
Pierce (2008)
Yellow AR-1 (Barnett and Pierce, 2008) Red
Scenario I Green Scenario II Blue Scenario II
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Probability of drying in a given year
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Climate Change 20 reduction Shortage Statistics
Shortage Frequency
Shortage Volume (MaF)
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Climate Change 10 reduction Shortage Statistics
Shortage Frequency
Shortage Volume (MaF)
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Sensitivity to Initial Demand Climate Change
20 reduction
Initial Demand 12.7MaF Actual Average
Consumption In the recent decade
Initial Demand 13.5MaF
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Sensitivity to Initial Demand Climate Change
10 reduction
Initial Demand 12.7MaF Actual Average
Consumption In the recent decade
Initial Demand 13.5MaF
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Climate Change 20 reduction Shortage Statistics
Shortage Frequency
Shortage Volume (MaF)
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Sensitivity to Initial Demand Climate Change
20 reduction Shortage Volume
Initial Demand 13.5MaF
Initial Demand 12.7MaF
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Summary

• Interim Guidelines (EIS) are pretty robust
• Until 20206 these guidelines are as good as any
  in reducing risk
• Water supply risk (i.e., risk of drying) is small
  (lt 5) in the near term 2026, for any climate
  variability (good news)
• Risk increases dramatically by about 7 times in
  the three decades thereafter (bad news)
• Risk increase is highly nonlinear
• There is flexibility in the system that can be
  exploited to mitigate risk.
• Considered alternatives provide ideas
• Smart operating policies and demand growth
  strategies need to be instilled
• Demand profiles are not rigid
• Delayed action can be too little too late
• Risk of various subsystems need to be assessed
  via the basin wide decision model (CRSS)