Transcript KWOC-presentation - Civil, Environmental and Architectural

Climate, Growth and Drought Threat
to Colorado River Water Supply
Balaji Rajagopalan
Department of Civil, Environmental and Architectural
Engineering
And
Cooperative Institute for Research in Environmental Sciences
(CIRES)
University of Colorado
Boulder, CO
Presentation to KOWACO
February 3, 2009
Collaborators

Kenneth Nowak
- CEAE / CADSWES
Edith Zagona
- CADSWES
James Prairie - USBR, Boulder

Ben Harding
- AMEC, Boulder
Marty Hoerling
Joe Barsugli
Brad Udall
Andrea Ray
-






NOAA
CIRES/WWA/NOAA
CIRES/WWA/NOAA
NOAA
A Water Resources Management
Perspective
Inter-decadal
Decision Analysis: Risk + Values
T
• Facility Planning
i
m
– Reservoir, Treatment Plant Size
e
• Policy + Regulatory Framework
H
o
r
i
z
o
n
Climate
– Flood Frequency, Water Rights, 7Q10 flow
• Operational Analysis
– Reservoir Operation, Flood/Drought Preparation
• Emergency Management
– Flood Warning, Drought Response
Data: Historical, Paleo, Scale, Models
Hours
Weather
Modeling Framework
What Drives Year to Year
Variability in regional
Hydrology?
(Floods, Droughts etc.)
Hydroclimate Predictions – Scenario
Generation
(Nonlinear Time Series Tools,
Watershed Modeling)
Decision Support System
(Evaluate decision
strategies
Under uncertainty)
Diagnosis
Forecast
Application
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/
•[email protected]
•[email protected]
Colorado River Basin Overview

7 States, 2 Nations







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





Source:Reclamation


1 acre-foot = 325,000 gals, 1 maf = 325 * 109 gals
1 maf = 1.23 km3 = 1.23*109 m3
Upper Basin: CO, UT, WY, NM
Lower Basin: AZ, CA, NV
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
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 ->14.1
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?
Colorado River Demand - Supply
20
Total Colorado River Use 9-year moving average.
18
NF Lees Ferry 9-year moving average
16
12
10
8
6
4
2
Calnder Year
19
98
20
02
20
06
19
94
19
90
19
86
19
82
19
78
19
74
19
70
19
66
19
62
19
58
19
54
19
50
19
46
19
42
19
38
19
34
19
30
19
26
19
22
19
18
0
19
14
Annual Flow (MAF)
14
Declining
Lakes
Mead and
Powell
30
25
Lake Mead Volume in Millions of Acrefeet
1935-2008
20
15
10
120 Foot drop
13 maf lost
Current: ~48%, 12 maf
5
0
30
Lake Powell Volume in Millions of Acrefeet
1963-2008
25
5 Years of 10 maf/yr
66% of average flows
Worst drought in
historic record
20
15
10
5
75 Foot Drop (Max 140)
10.5 maf lost
Current: ~56%, 14.5 maf
1963
1965
1966
1968
1969
1971
1972
1974
1975
1977
1978
1980
1981
1983
1984
1986
1987
1989
1990
1992
1993
1995
1996
1998
1999
2001
2002
2004
2005
2007
0
New York Times Sunday
Magazine, October 21, 2007
Dropping Lake Mead
Lake Mead’s
Delta Circa 1999
Lake Powell – June 29, 2002
~2004
~1999
Lake Powell – December 23, 2003
Source: USGS, Reclamation
Recent conditions in the
Colorado River Basin
Paleo 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
Colorado River at Lees Ferry, AZ




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
5 year running average
observed record
Woodhouse et al.
2006
Stockton and Jacoby,
1976
Hirschboeck and
Meko, 2005
Hildalgo et al. 2002
Past Flow Summary

Paleo reconstructions indicate
th century one of the most wettest
 20
 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?
Future Climate
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
IPCC 2007 AR4 Projections


Wet get wetter and dry get drier…
Southwest Likely to get drier
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
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
Progression of Data and Models in studies about the influence of climate change on streamflows in
the Colorado River Basin
1.
Climate Change Data
Source
3.
Water Supply
Operations
Model
2.
Flow Generation
Technique
General
CirculationModel
Regression
Temperature
Precipitation
Hypothetical
Scenarios
OR
Hydrology Models:
NWSRFS
VIC
PRMS
Streamflow
CRSS
CRMM
Reservoir storage
Hydroelectric power
UB Releases
Stuff
and m
Study
Climate
Change
Technique
(Scenario/GC
M)
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- TemperaturePrecipitation 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,
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 subbasins 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.
-10% Precip only =
-11% runoff.
Green = 2010-2039
Blue = 2040-2069
Red = 2070-2099
120
110
100
90
80
-40% to
+30%
Runoff
changes in
2070-2099
~80%
70
Up
= Increase
Down = Decrease
2C to 6 C
60
Triangle size
proportional to
runoff changes:
~115%
Precip Change in %
CRB
Runoff
From
C&L
Precipitation, Temperatures and Runoff in 2070-2099
0
1
2
3
Temp Increase in C
4
5
6
Colorado River Climate Change Studies over the
Years

Early Studies – Scenarios, About 1980



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







Stockton and Boggess, 1979
Revelle and Waggoner, 1983*
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
•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
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
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
Streamflow Simulation
•Paleo
•Observations
•Need to Combine
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.
Proposed Framework Prairie et al. (2008, WRR)
Nonhomogeneous Markov Chain
Model on the observed & Paleo
data
Natural
Climate
Variability
Generate system state
( St )
Generate flow conditionally
(K-NN resampling of historical flow)
f ( xt St , St 1 , xt 1 )
10000 Simulations
Each 50-year long
2008-2057
Superimpose Climate Change
trend (10% and 20%)
Climate
Change
window = 2h +1
Discrete
3h
kernel K ( x) 
(1  x 2 ) for x  1
2
(1  4h )
function
Source: Rajagopalan et al., 1996
h
Nonhomogenous Markov model with Kernel smoothing
(Rajagopalan et al., 1996)

Transition Probability (TP) for each year are obtained
using a discrete Kernel Estimator
 t  t dwi 

K 

hdw 
i 1

Pdw (t )  nd
 t  tdi 

K 

i 1
 hdw 
ndw
Pdd (t )  1  Pdw (t )

h determined with LSCV
LSCV (h) 

1 n
[1  Pˆti (t i )] 2

n i 1
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)
Transition Probabilities
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 j+1 is the simulated flow, Xt+1
Generate flow conditionally
(K-NN resampling of historical flow)
f ( xt St , St 1 , xt 1 )
Drought and Surplus Statistics
flow
Surplus
Length
Drought
Length
Surplus
volume
Threshold
(e.g., median)
time
Drought Deficit
Drought/Surplus Statistics
K-NN-1 bootstrap
Of observed flow
Paleo + Obs
Red  Paleo stat
Blue  Observed stat
Storage Statistics
60
System Risk
•Streamflow Simulation
• System Water Balance
Model
•Management Alternatives
(Reservoir Operation +
Demand Growth)

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
UC CRSS stream gauges
LC CRSS stream gauges
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 Lee’s 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
Combined Area-volume Relationship
ET Calculation
ET (MaF)
2
1.5
1
0.5
0
0
10
20
30
40
Storage (MaF)
50
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
60
70
Management and Demand Growth Combinations
A.
B
C.
D.
E.
F.
G.
The interim EIS operational policies employed with demand growing
based on the upper basin depletion schedule.
with the demand fixed at the 2008 level ~ 13.5MaF
Same as A but with larger delivery shortages
Same as C but with a 50% reduced upper basin depletion schedule.
Same as A with full initial storage.
Same as A but post 2026 policy that establishes new shortage
action thresholds and volumes.
Demand fixed at 2008 level and post 2026 new shortage action.
All the reservoir operation policies take effect from 2026
INTERIM EIS
INTERIM PLUS
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
Flow and Demand Trends
applied to the simulations
Red – demand trend
13.5MAF – 14.1MAF
by 2030
Blue – mean flow trend
15MAF – 12MAF
By 2057
-0.06MAF/year
Under 20% - reduction
Flow trend with sample simulation
37.2% of simulations > 15MAF
22.3% of simulations > 17MAF
34.7% of simulations > 15MAF
18.8% of simulations > 17MAF
PDF of generated streamflows (boxplots)
PDF of observed flow (red)
AR-1
NHMM
Natural Climate Variability
Climate Change – 20% reduction
Climate Change – 10% reduction
When Will Lake Mead Go Dry?
Water Resources Research, 2008

Water Budget Analysis



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



One 50 maf reservoir, increasing UB demands (13.5 in 2008 ->14.1 maf/yr
in 2030, 15.1 maf /yr inflows, current starting contents
Linear Climate Change Reduction in Flows w/ some natural variability
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
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
Probability of drying in a given year
Climate Change – 20% reduction
Shortage Statistics
Shortage Frequency
Shortage Volume (MaF)
Climate Change – 10% reduction
Shortage Statistics
Shortage Frequency
Shortage Volume (MaF)
Sensitivity to Initial Demand
Climate Change – 20% reduction
Initial Demand – 12.7MaF
Actual Average Consumption
In the recent decade
Initial Demand – 13.5MaF
Sensitivity to Initial Demand
Climate Change – 10% reduction
Initial Demand – 12.7MaF
Actual Average Consumption
In the recent decade
Initial Demand – 13.5MaF
Climate Change – 20% reduction
Shortage Statistics
Shortage Frequency
Shortage Volume (MaF)
Sensitivity to Initial Demand Climate Change – 20% reduction
Shortage Volume
Initial Demand
~13.5MaF
Initial Demand
~12.7MaF
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 (< 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)