Transcript Effects of Climate Change on Streamflow and Water Resources

Effects of Climate Change on
Streamflow and Water Resources
Management in the Columbia River
Basin
JISAO Center for Science in the Earth System
Climate Impacts Group
and Department of Civil and Environmental Engineering
University of Washington
Oct, 2005
Alan F. Hamlet
Philip W. Mote
Dennis P. Lettenmaier
Hydroclimatology of the Pacific Northwest
Columbia River Basin
Useable Storage ~35 MAF
~50% of storage is in Canada
~Storage is 30% of annual flow
Snowpack functions as a
natural reservoir
Elevation (m)
Annual PNW Precipitation (mm)
The Dalles
Sensitivity of Snowmelt and Transient Rivers
to Changes in Temperature and Precipitation
900000
700000
600000
500000
400000
300000
200000
100000
1974
1974
1974
1974
1974
1974
1974
1974
1974
1974
1973
1973
1973
1973
1973
0
1973
•Streamflow timing is altered
• Annual volume stays about
the same
800000
Flow (cfs)
Temperature warms,
precipitation unaltered:
Water Year
900000
800000
600000
500000
400000
300000
200000
100000
1974
1974
1973
1973
1973
1973
1973
0
1973
•Streamflow timing stays about the same
•Annual volume is altered
700000
Flow (cfs)
Precipitation increases,
temperature unaltered:
Water Year
Effects of the PDO and ENSO on Columbia River
Summer Streamflows
PDO
450000
Cool
Cool
Warm
Apr-Sept Flow (cfs)
400000
Warm
350000
300000
250000
200000
high
high
low
low
Ocean Productivity
2000
1990
1980
1970
1960
1950
1940
1930
1920
1910
1900
150000
Log10 mean flow, The Dalles, OR (cfs)
The Dust Bowl was probably not the worst drought sequence
in the past 250 years.
5.5
red = observed, blue = reconstructed
5.4
5.3
5.2
5.1
5.0
1750
1775
1800
1825
1850
1875
Year
1900
1925
1950
1975
Source: Gedalof, Z., D.L. Peterson and Nathan J. Mantua. (in review). Columbia
River Flow and Drought Since 1750. Submitted to Journal of the American
Water Resources Association.
2000
Observed Hydrologic Changes
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 (in press)
Trends in timing of
peak snowpack are
towards earlier
calendar dates
Change in Date
As the West warms,
winter flows rise
and summer flows
drop
Stewart IT, Cayan DR,
Dettinger MD, 2004,
Changes toward earlier
streamflow timing across
western North America, J.
Climate (in review)
Global Climate Change Scenarios
and Hydrologic Impacts for the PNW
Four Delta Method Climate Change Scenarios for the PNW
Delta T, 2020s
Delta T, 2040s
5
5
~ + 1.7 C
~ + 2.25 C
4
hadCM2
3
hadCM3
2
PCM3
ECHAM4
1
Degrees C
Degrees C
4
mean
0
hadCM2
3
hadCM3
2
PCM3
ECHAM4
1
mean
0
J
F
M
A
M
J
J
A
S
O
N
D
J
-1
F
M
A
Precipitation Fraction, 2020s
J
J
A
S
O
N
D
Precipitation Fraction, 2040s
1.75
1.75
1.5
1.5
hadCM2
hadCM3
1.25
PCM3
1
ECHAM4
Fraction
Fraction
M
-1
hadCM2
hadCM3
1.25
PCM3
1
ECHAM4
mean
0.75
mean
0.75
0.5
0.5
J
F
M
A
M
J
J
A
S
O
N
D
J
F
M
A
M
J
J
A
S
O
N
D
Somewhat wetter winters and perhaps somewhat dryer summers
Changes in Mean
Temperature and
Precipitation or Bias
Corrected Output
from GCMs
VIC
Hydrology Model
ColSim
Reservoir
Model
Changes in Simulated April 1
Snowpack for the Cascade Range
in Washington and Oregon
(% change relative to current climate)
Current Climate
“2020s” (+1.7 C)
-44%
April 1 SWE (mm)
“2040s” (+ 2.25 C)
-58%
Changes in Simulated April 1
Snowpack for the Canadian
and U.S. portions of the
Columbia River basin
base
comp2020
comp2040
whole basin
0.00
-14.86
-26.28
canada
0.00
-3.56
-11.51
US
0.00
-21.35
-34.79
(% change relative to current climate)
Current Climate
“2020s” (+1.7 C)
-3.6%
-21.4%
April 1 SWE (mm)
“2040s” (+ 2.25 C)
-11.5%
-34.8%
Naturalized Flow for Historic and Global Warming Scenarios
Compared to Effects of Regulation at 1990 Level Development
Historic Naturalized Flow
Estimated Range of
Naturalized Flow
With 2040’s Warming
Regulated Flow
Changes in Natural Streamflow for the “Middle of the Road” Scenarios
Current Climate--Blue
2020s--Green
2040s--Red
Impacts in the
upper basin
(Canada) are
delayed in
comparison
with the lower
basin (USA).
Effects of streamflow timing shifts and precipitation changes
on drought frequency in the Okanogan Basin
(Plot shows frequency of April-July flows below 1 million acre-ft in the Similkameen
River at Nighthawk)
70
Drought Risk (%)
60
50
40
drought risk %
30
20
10
0
historic
2003
climate
comp
2040
mpi 2040 hc 2040
Effects of Hydrologic Changes
Increased Winter Flow
Increases winter flooding in some basins
Potential benefits to winter hydro production
Reduced Snowpack and Earlier Snow Melt
Reduces spring flooding in some basins
Reduces summer water availability (limited storage)
Reduces summer hydro production
Increased summer drought frequency
Late summer streamflows systematically lower
Increased water temperatures
Decadal Climate Variability and Climate
Change
Will Global Warming be “Warm and
Wet” or “Warm and Dry”?
Answer:
Probably BOTH!
450000
350000
300000
250000
200000
2000
1990
1980
1970
1960
1950
1940
1930
1920
1910
150000
1900
Apr-Sept Flow (cfs)
400000
Sustainable management of PNW water resources will very likely have to cope
with flow variability associated with both “warm and wet” and “warm and dry”
scenarios at different times. Such conditions can be incorporated in planning as
a test for sustainability though adverse periods, rates of recovery during
favorable periods, etc.
Natural Streamflows at Dworshak
20000
18000
Average Streamflow (cfs)
16000
Cool PDO
2040
14000
12000
10000
Warm PDO
2040
Base
2040_warm_PDO
2040_cool_PDO
8000
6000
4000
2000
0
O
N
D
J
F
M
A
M
J
J
A
S
Water Resources Implications for the Columbia
River Basin
Hydropower Production
•Annual hydropower resources will follow annual flow regimes, which
are mostly strongly related to uncertain changes winter precipitation.
We expect that these values will be higher or lower at different times
in the future (as in the 20th century).
•Summer electricity demand is expected to increase over time as
customers in the PNW install more a/c equipment and warming
increases the number of cooling degree days. Winter demand is
expected to decrease somewhat. Shifts in the seasonal timing of
hydropower production may be required to meet these changing
demands (more use of storage in summer).
•In isolation, Columbia basin winter hydropower production is
relatively robust to streamflow timing shifts, but winter hydro
production will be affected by the need to mitigate impacts to other
system objectives such as flood control and instream flow
augmentation.
Irrigation
•Irrigation from Columbia River main stem projects will probably not be
substantially affected by streamflow timing shifts.
•Temperature sensitive basins (e.g. the Okanogan and Yakima basins)
will likely see reduced summer water supplies and increased conflicts
between instream flow augmentation, water temperature control, and
water supply.
•In isolation, the upper Snake River irrigation projects may see little
reduction in summer water supply over the next 50 years or so unless
winter precipitation systematically declines (high elevation snow
fields). Considerable reservoir storage in this part of the basin can
also largely compensate for the modest streamflow timing shifts
expected. Increased conflicts between the need to maintain instream
flow and water temperature regimes (Dworshak dam) in the lower
basin and conjunctive management of surface and groundwater
irrigation rights farther upstream are expected to follow warming in this
basin.
Managed Flow Augmentation
•The flow needed to provide acceptable flow velocity for juvenile
transport is frequently higher than natural flow, particularly in late
summer (I.e. use of storage is required). Climate change increases
the amount of storage required to meet flow targets.
•Currently very little storage is allocated to fish in comparison with
hydropower.
40000
Hydro storage
System Storage (kAF)
35000
30000
25000
20000
15000
10000
Fish flow storage
5000
0
1
•In a conflict between hydro or irrigation and fish flow, the current
reservoir operating policies are designed to protect hydro and
irrigation (fish flow storage allocation for main stem and Snake River
flow targets is at the top of a shared reservoir storage pool)
•The Columbia River Treaty does not provide explicitly for summer
flow in the U.S. (see transboundary issues).
Adaptation to climate change will require complex tradeoffs
between ecosystem protection and hydropower operations
Percent of Control Run Climate
2070-2098
140
PCM Control Climate and
Current Operations
120
PCM Projected Climate
and Current Operations
100
PCM Projected Climate
with Adaptive
Management
80
60
Firm
Hydropower
Annual Flow
Deficit at
McNary
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
Flood Control vs. Refill
Maintaining an appropriate balance between flood protection
and the reliability of reservoir refill is crucial to many water
resources objectives in the Columbia Basin.
As streamflow timing shifts move peak flows earlier in the
year, flood evacuation schedules may need to be revised both
to protect against early season flooding and to begin refill
earlier to capture the (smaller) spring freshet.
Model experiments (see Payne et al. 2004) have shown that
moving flood evacuation two weeks to one month earlier in
the year helps mitigate reductions in refill reliability associated
with streamflow timing shifts.
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
Water Temperature
Higher air temperatures and increased residence time in
reservoirs due to summer streamflow reductions are likely to
systematically increase water temperatures throughout the
basin.
In managed basins, stored cold water in reservoirs may be
exhausted more rapidly than now, reducing the ability to
mitigate high stream temperatures using releases from
storage, particularly in late summer. Cold water storage at
Dworshak dam is a particular concern since it is one of the
few dams available to control stream temperatures in the
lower Snake and is sited in a sensitive area.
Implications for Transboundary
Agreements
•Snowpack in the BC portion of the Columbia basin is much less
sensitive to warming in comparison with portions of the basin in the
U.S. and streamflow timing shifts will also be smaller in Canada.
•Over the next 50 years or so, Canada will have an increasing fraction
of the snowpack contributing to summer streamflow volumes in the
Columbia basin.
•These differing impacts in the two countries have the potential to
“unbalance” the current coordination agreements, and will present
serious challenges to meeting instream flows on the U.S. side.
•Changes in flood control, hydropower production, and instream flow
augmentation will all be needed.
•Long-range planning is needed to address these issues.
Broad Strategies for Incorporating Climate Variability and
Climate Change in Long-Term Planning
Identify and Assess Climate Linkages
Identify potential linkages between climate and resource management that could
affect outcomes in the long term. What’s being left out? Are there future “deal
breakers” in these omissions? (e.g. ocean productivity, glaciers maintaining
summer streamflow in the short term)
Design for Robustness and Sustainability
Use modeling studies to test preferred management alternatives for robustness in
the face of climate variability represented by paleoclimatic studies, conventional
observations, decadal variability, and future climate change projections.
Identify Limits and Increase Response Capability
Use estimates of uncertainties or “what if” scenarios to find the performance limits
inherent in preferred management alternatives. How can response capability be
increased?
Expect Surprises and Design for Flexibility to Changing Conditions
Design contingency planning into management guidelines to allow for ongoing
adaptation to unexpected (or uncertain) conditions without recursive policy
intervention.
Selected References and URL’s
Climate Impacts Group Website
http://www.cses.washington.edu/cig/
White Papers, Agenda, Presentations for CIG 2001 Climate Change Workshop
http://jisao.washington.edu/PNWimpacts/Workshops/Skamania2001/WP01_agenda.htm
Climate Change Streamflow Scenarios for Water Planning Studies
http://www.ce.washington.edu/~hamleaf/climate_change_streamflows/CR_cc.htm
Northwest Power and Conservation Council Columbia Basin Hydropower Study
http://www.nwppc.org/energy/powerplan/plan/Default.htm
Refs on Climate Variability and Climate Change
http://www.ce.washington.edu/~hamleaf/hamlet/publications.html