Alan F. Hamlet,

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Effects of Climate Change and Climate Variability
on USBR Missions in the Western U.S.

• Alan F. Hamlet,
• Philip W. Mote,
• Dennis P. Lettenmaier
• JISAO/CSES Climate Impacts Group
• Dept. of Civil and Environmental Engineering
• University of Washington

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Example of a flawed water planning study The
Colorado River Compact of 1922
The Colorado River Compact of 1922 divided the
use of waters of the Colorado River System
between the Upper and Lower Colorado River Basin.
It apportioned in perpetuity to the Upper and
Lower Basin, respectively, the beneficial
consumptive use of 7.5 million acre feet (maf) of
water per annum. It also provided that the Upper
Basin will not cause the flow of the river at Lee
Ferry to be depleted below an aggregate of 7.5
maf for any period of ten consecutive years. The
Mexican Treaty of 1944 allotted to Mexico a
guaranteed annual quantity of 1.5 maf. These
amounts, when combined, exceed the river's
long-term average annual flow.       
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Whats the Problem?
Despite a general awareness of these issues in
the water planning community, there is growing
evidence that future climate variability will not
look like the past and that current planning
activities, which frequently use a limited
observed streamflow record to represent climate
variability, are in danger of repeating the same
kind of mistakes made more than 80 years ago in
forging the Colorado River Compact. Long-term
water supply planning and specific agreements
influenced by this planning (e.g. water
allocation agreements) should be informed by the
best and most complete climate information
available, but frequently they are not.
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Cool Season Climate of the Western U.S.
PNW
GB
CA
CRB
DJF Temp (C)
NDJFM Precip (mm)
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Until mid-century, emissions scenarios play a
minor role in the temperature impacts. Towards
the end of the century they play a big role.
Conclusions 1) Adaptation will be an essential
component of the response to warming over the
next 50 years. 2) Mitigation of greenhouse gas
emissions will play an important role in
determining the scope of late 21st century
impacts.
3.2C
C
1.7C
0.7C
1.2-5.5C
0.9-2.4C
Observed 20th century variability
0.4-1.0C
Pacific Northwest
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-1 to 3
6
2
1
Observed 20th century variability
-2 to 21
-1 to 9
Pacific Northwest
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Recession of the Muir Glacier
Aug, 13, 1941
Aug, 31, 2004
Image Credit National Snow and Ice Data Center,
W. O. Field, B. F. Molnia http//nsidc.org/data/gl
acier_photo/special_high_res.html
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Collapse of the Larsen B Ice shelf, Antarctica
March 5, 2002
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Bark Beetle Outbreak in British Columbia
(Figure courtesy Allan Carroll)
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Hydrologic Changes Associated with Warming
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The warmest locations that accumulate snowpack
are most sensitive to warming
2.3C, 6.8 winter precip
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Changes in Simulated April 1 Snowpack for the
Canadian and U.S. portions of the Columbia River
basin ( change relative to current climate)
20th Century Climate
2040s (1.7 C)
2060s ( 2.25 C)
-3.6
-11.5
-21.4
-34.8
April 1 SWE (mm)
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Climate change assessments using scenarios show
significant hydrologic changes due to temperature
in basins with substantial snow accumulation in
winter.
20th Century
Change
2.25 C
Naches River Basin on the East Slopes of the
Cascades.
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Simulated Changes in Natural Runoff Timing in the
Naches River Basin Associated with 2 C Warming

• Increased winter flow
• Earlier and reduced peak flows
• Reduced summer flow volume
• Reduced late summer low flow

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Trends in April 1 SWE 1950-1997
Mote P.W.,Hamlet A.F., Clark M.P., Lettenmaier
D.P., 2005, Declining mountain snowpack in
western North America, BAMS, 86 (1) 39-49
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As the West warms, spring flows rise and summer
flows drop Stewart IT, Cayan DR, Dettinger MD,
2005 Changes toward earlier streamflow timing
across western North America, J. Climate, 18 (8)
1136-1155
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Water Supply Impacts
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Water Supply Impact Pathways
Reductions in Supply
Climate Change
Combined Impacts
Increases in Demand
Increasing Population
Conflicts with Other Water Resources Objectives
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In Managed Systems the Storage to Flow Ratios are
Important
High Storage to Flow Ratio (e.g. the Colorado
River basin) Low sensitivity to streamflow
timing shifts, high sensitivity to systematic
changes in precipitation and multi-year
drought Low Storage to Flow Ratio (e.g. the
Seattle Water Supply System) High sensitivity
to streamflow timing shifts and changes in single
year droughts.
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• Transient SWE simulation from HadCM3 (A2) GCM run
  (with running 10 year average smoothing)
• Simulated from observed climate shows a declining
  trend of 3KAF per decade (1935-2000)
• HadCM3 simulated declines 4KAF per decade

Figure courtesy of Matt Wiley and Richard Palmer
at CEE, UW
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In sensitive areas, systematic reductions in
summer water availability will affect the yield
of water supply systems.
Master's Thesis Wiley, M.W. (2004). "Analysis
Techniques to Incorporate Climate Change
Information into Seattles Long Range Water
Supply Planning," University of Washington
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Flood Control vs Reservoir Refill
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Flood Control vs. Refill
Full
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Flood Control vs. Refill
Streamflow timing shifts can reduce the
reliability of reservoir refill
2.25 oC
Full
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Flood Control vs. Refill
Streamflow timing shifts can reduce the
reliability of reservoir refill
2.25 oC
Full
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Major U.S. Flood Control Checkpoints
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Changes in Reservoir Storage
Se-Yeun Lee et al., 2007, Optimized Flood Control
in the Columbia River Basin for a Global Warming
Scenario, ASCE J. Water Resources Planning and
Management (submitted)
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Instream Flow Augmentation and Water Quality
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Simulated Changes in Natural Runoff Timing in the
Naches River Basin Associated with 2 C Warming

• Increased winter flow
• Earlier and reduced peak flows
• Reduced summer flow volume
• Reduced late summer low flow

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Climate change adaptation may involve complex
tradeoffs between competing system objectives
Source Payne, J.T., A.W. Wood, A.F. Hamlet, R.N.
Palmer and D.P. Lettenmaier, 2004, Mitigating the
effects of climate change on the water resources
of the Columbia River basin, Climatic Change Vol.
62, Issue 1-3, 233-256
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Temperature thresholds for coldwater fish in
freshwater

• Warming temperatures will increasingly stress
  coldwater fish in the warmest parts of our region
• A monthly average air temperature of 68ºF (20ºC)
  has been used as an upper limit for resident cold
  water fish habitat, and is known to stress
  Pacific salmon during periods of freshwater
  migration, spawning, and rearing

1.7 C
2.3 C
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Streamflow Forecasting Implications

• Loss of snowpack due to warming, and projected
  increases in precipitation variability may
  increase streamflow forecast uncertainties
• Statistical forecasting procedures may not be
  robust to new conditions related to vegetation
  changes or long term changes in ground water
  (need for alternative forecasting tools).

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Super ensemble CDFs of PNW winter precipitation
for four 30 year time slices from nine GCM
simulations
Sample Size 270 years
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Regionally Averaged Cool Season Precipitation
Anomalies
PRECIP
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Adaptation
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Approaches to Adaptation

• Anticipate changes. Accept that the future
  climate will be substantially different than the
  past.
• Use scenario based planning to evaluate
  alternatives rather than the historic record.
  (Institutional challenges)
• Expect surprises and design for flexibility and
  robustness in the face of uncertain changes
  (particularly when sensitivity to precipitation
  changes dominates).
• Plan for the long haul. Where possible, make
  adaptive responses self tending to avoid
  repetitive costs of policy intervention as
  impacts increase over time.

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Conclusions Global climate change is expected
to result in important hydrologic changes in the
western U.S. because of impacts to snowpack and
streamflow timing. Some important impact
pathways related to USBR missions include
impacts to summer water supply, balance of flood
control and reservoir refill, streamflow
augmentation and water quality, streamflow
forecasting uncertainty. Wide-spread
institutional obstacles currently exist that
would effectively prevent the use of
scenario-based planning procedures, yet use of
the historic streamflow record for risk
assessment and long-range planning is expected to
become increasingly problematic as the climate
warms.