Download Hydrological Impacts of Global Climate Change

Hydrological Impacts of Global
Climate Change
Center for Science in the Earth System
Climate Impacts Group
and Department of Civil and Environmental Engineering
University of Washington
May, 2005
http://www.hydro.washington.edu/Lettenmaier/Presentations/2005/hamlet_WA_water_law_may_2005.ppt
Alan F. Hamlet Philip W. Mote
Martyn Clark
Dennis P. Lettenmaier
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**.
What’s 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 planning and specific agreements influenced by
this planning (such as the long-term licensing of hydropower
projects and water permitting) should be informed by the best
and most complete climate information available, but
frequently they are not.
Annual PNW Precipitation (mm)
Elevation (m)
(mm)
Winter
Precipitation
Summer
Precipitation
Hydrologic Characteristics of PNW Rivers
Normalized Streamflow
3.0
2.5
Snow
Dominated
2.0
Transient Snow
1.5
Rain Dominated
1.0
0.5
0.0
10 11 12
1
2
3
4
Month
5
6
7
8
9
Sensitivity of Snowmelt and Transient Rivers
to Changes in Temperature and Precipitation
900000
800000
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
700000
Flow (cfs)
Temperature warms,
precipitation unaltered:
Water Year
900000
600000
500000
400000
300000
200000
100000
1974
1974
1973
1973
1973
1973
1973
0
1973
•Streamflow timing stays
about the same
•Annual volume is increases
700000
Flow (cfs)
Precipitation increases,
temperature unaltered:
800000
Water Year
Four Delta Method Climate Change Scenarios for the PNW
Delta T, 2020s
Delta T, 2040s
5
5
~ + 1.7 C
~ + 2.5 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
Schematic of VIC Hydrologic Model and Energy Balance Snow Model
PNW
GB
CA
CR
B
Snow Model
Changes in Simulated
April 1 Snowpack for the
Cascade Range in
Washington and Oregon
Current Climate
“2020s” (+1.7 C)
-44%
April 1 SWE (mm)
“2040s” (+ 2.5 C)
-58%
Climate change assessments using scenarios show significant
hydrologic changes due to temperature in basins with substantial
snow accumulation in winter.
600
400
snow water equiv.
runoff+baseflow
-200
soil storage
evapotranspiration
100
sep
aug
jul
jun
may
apr
mar
feb
jan
dec
nov
0
Naches River Basin on the East
Slopes of the Cascades.
sep
aug
jul
jun
-250
may
200
precipitation
-150
apr
300
oct
Area Average Water
(depth in mm)
400
-100
mar
+ 2.5 °C
500
-50
feb
600
0
jan
sep
aug
jul
jun
may
apr
mar
feb
jan
dec
nov
oct
0
50
dec
100
100
nov
200
150
oct
300
Changes in Long Term Water Balance (mm of
water)
Area Average Water
(depth in mm)
500
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
Man-made storage ~ 30% of annual flow
Effects to the Cedar River (Seattle Water Supply)
for “Middle-of-the-Road” Scenarios
9000
8000
+1.7 C
6000
Simulated 20th
Century Climate
2020s Climate
Change Scenario
2040s Climate
Change Scenario
5000
4000
3000
2000
+2.5 C
1000
Date
9/2
8/5
7/8
6/10
5/13
4/15
3/18
2/18
1/21
12/24
11/26
10/29
0
10/1
Inflow (acre-ft)
7000
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
Hydrologic Impacts for the Cascades
Obs. Summer Water Availability is Declining
0.7
Cedar River: -30.7%
May-Sept frac
Linear (May-Sept
frac)
0.5
0.4
0.3
0.2
0.6
SFTolt River: -15.7%
May-Sept frac
y = -0.0020x + 4.3416
0.1
0
1945
1955
1965
1975
55 years
1985
1995
2005
May-Sept fraction of annual flow
May-Sept fraction of annual flow
0.6
Linear (May-Sept
frac)
0.5
0.4
0.3
0.2
y = -0.0010x + 2.2890
0.1
0
1945
1955
1965
1975
1985
1995
Figures courtesy of Matt Wiley and Richard Palmer at CEE, UW
2005
Cascades Sub Domain
Elevation (m)
Trends in April 1 SWE for the WA and OR Cascades
600
-19%
500
400
Effects of Temperature
And Precipitation
1-Apr
300
Linear (1-Apr)
200
-2.15% per decade
100
y = -0.5851x + 295.29
2001
1996
1991
1986
1981
1976
1971
1966
1961
1956
1951
1946
1941
1936
1931
1926
1921
1916
0
500
-25%
450
400
350
300
Effects of Temperature
Alone
1-Apr
250
Linear (1-Apr)
200
150
100
50
2001
1996
1991
1986
1981
1976
1971
1966
1961
1956
1951
1946
1941
1936
1931
1926
1921
0
1916
-2.84% per decade
y = -0.7553x + 301.86
Trends in April 1 SWE for the WA and OR Cascades
600
-35%
500
400
Effects of Temperature
And Precipitation
1-Apr
Linear (1-Apr)
300
200
-6.48% per decade
100
y = -1.739x + 313.96
2001
1998
1995
1992
1989
1986
1983
1980
1977
1974
1971
1968
1965
1962
1959
1956
1953
1950
0
400
-23%
350
300
250
Effects of Temperature
Alone
1-Apr
Linear (1-Apr)
200
150
y = -1.1264x + 288.63
100
50
2001
1998
1995
1992
1989
1986
1983
1980
1977
1974
1971
1968
1965
1962
1959
1956
1953
0
1950
-4.25% per decade
Combined Cedar-Tolt basin wide average April 1 SWE
Simulated from HadCM3
Simulated from Observed Climate
Linear (Simulated from HadCM3)
Linear (Simulated from Observed Climate)
KAF
100
50
0
1935
1955
1975
1995
2015
2035
2055
• 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 (19352000)
• HadCM3 simulated declines ~4KAF per decade
Figure courtesy of Matt Wiley and Richard Palmer at CEE, UW
2075
Conclusions
•Loss of snowpack is one of the most important impact
pathways associated with global warming in the PNW.
•Hydrologic changes associated with warming include earlier
and reduced peak snowpack, increased flows in winter, earlier
and reduced spring and summer runoff, and decreased low
flows in late summer.
•Large-scale changes in the seasonal dynamics of snow
accumulation and melt have already occurred in the West.
•The most sensitive areas are coastal mountain ranges with
relatively warm winter temperatures such as the Cascades
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
Refs on Climate Variability and Climate Change
http://www.ce.washington.edu/~hamleaf/hamlet/publications.html