Transcript Hydrologic Implications of Climate Change for the Western US

Hydrologic Implications of Climate
Change for 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
Climatological Foundation of U.S. Water
Resources Planning and Management:
1) Risks are stationary in time.
2) Observed streamflow records are the best estimate of
future variability.
3) Systems and operational paradigms that are robust to
past variability are robust to future variability.
The Myth of Stationarity Meets the
Death of Stationarity
Muir Glacier in Alaska
Aug, 13, 1941
Aug, 31, 2004
Image Credit: National Snow and Ice Data Center, W. O. Field, B. F. Molnia
http://nsidc.org/data/glacier_photo/special_high_res.html
Global Climate Change Scenarios
and Hydrologic Impacts for the PNW
Cool Season Climate of the Western U.S.
PNW
GB
CA CRB
DJF Temp (°C)
NDJFM Precip (mm)
Consensus Forecasts of Temperature and Precipitation Changes from IPCC AR4 GCMs
Observed 20th century variability
°C
+3.2°C
+1.7°C
+0.7°C
0.9-2.4°C
0.4-1.0°C
Pacific Northwest
1.2-5.5°C
Observed 20th century variability
%
-1 to +3%
+1%
+6%
+2%
-1 to +9%
Pacific Northwest
-2 to +21%
Will Global Warming be “Warm and
Wet” or “Warm and Dry”?
Answer:
450000
Probably BOTH!
Natural Flow Columbia River at The Dalles
350000
300000
250000
200000
2000
1990
1980
1970
1960
1950
1940
1930
1920
1910
150000
1900
Apr-Sept Flow (cfs)
400000
2000
1996
1992
1988
1984
1980
1976
1972
1968
1964
1960
1956
1952
1948
1944
1940
CRB
1936
CA
1932
1928
3
1924
1920
1916
Std Anomalies Relative to 1961-1990
Regionally Averaged Cool Season Precipitation Anomalies
4
PNW
PRECIP
GB
2
1
0
-1
-2
-3
Schematic of VIC Hydrologic Model and
Energy Balance Snow Model
Snow Model
The warmer locations are most
sensitive to warming
2060s
+2.3C,
+6.8%
winter
precip
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)
-3.6%
-21.4%
April 1 SWE (mm)
“2060s” (+ 2.25 C)
-11.5%
-34.8%
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
DJF avg T (C)
Overall Trends in April 1 SWE from 1947-2003
Trend %/yr
Trend %/yr
DJF avg T (C)
Temperature Related Trends in April 1 SWE from 1947-2003
Trend %/yr
Trend %/yr
DJF avg T (C)
Precipitation Related Trends in April 1 SWE from 1947-2003
Trend %/yr
Trend %/yr
Simulated Changes in Natural Runoff Timing in the Naches
River Basin Associated with 2 C Warming
120
Simulated Basin Avg Runoff (mm)
100
80
Impacts:
•Increased winter flow
•Earlier and reduced peak flows
•Reduced summer flow volume
•Reduced late summer low flow
1950
60
plus2c
40
20
0
oct
nov
dec
jan
feb
mar
apr
may
jun
jul
aug
sep
250
Simulated Basin Avg Runoff (mm)
Chehalis River
200
150
1950
plus2c
100
50
0
oct
nov
dec
jan
feb
mar
apr
may
jun
jul
aug
sep
500
Hoh River
Simulated Basin Avg Runoff (mm)
450
400
350
300
1950
250
plus2c
200
150
100
50
0
oct
nov
dec
jan
feb
mar
apr
may
jun
jul
aug
sep
200
Nooksack
River
Simulated Basin Avg Runoff (mm)
180
160
140
120
1950
100
plus2c
80
60
40
20
0
oct
nov
dec
jan
feb
mar
apr
may
jun
jul
aug
sep
Mapping of Sensitive Areas in the PNW by Fraction of
Precipitation Stored as Peak Snowpack
HUC 4 Scale Watersheds in the PNW
Climate Change Impacts are Similar to
Impacts of Water Management in PNW Hydropower Systems
30000
Estimated natural flows
Streamflow (cfs)
25000
20000
nat
15000
obs
10000
5000
Skagit River at Mt. Vernon
0
10
11
12
1
2
3
4
5
6
7
8
9
Changes in Flood Risk in the Western U.S.
Regionally Averaged Temperature Trends Over the Western U.S. 1916-2003
3.00
PNW
Linear Trend (Deg. C per century)
CA
PNW
1.50
1.00
0.50
0.00
-0.50
-1.00
nov
dec
jan
feb
mar
apr
may
jun
jul
aug
sep
4.00
Linear Trend (Deg. C per century)
CA CRB
GBAS
2.00
oct
GB
CRB
Tmax
2.50
CA
3.50
CRB
Tmin
GBAS
3.00
PNW
2.50
2.00
1.50
1.00
0.50
0.00
oct
nov
dec
jan
feb
mar
apr
may
jun
jul
aug
sep
DJF Avg Temp (C)
Simulated Changes in the 20-year Flood
Associated with 20th Century Warming
DJF Avg Temp (C)
X20 2003 / X20 1915
X20 2003 / X20 1915
X20 2003 / X20 1915
DJF Avg Temp (C)
20-year Flood for “1973-2003” Compared to “1916-2003” for a Constant
Late 20th Century Temperature Regime
X20 ’73-’03 / X20 ’16-’03
X20 ’73-’03 / X20 ’16-’03
Summary of Flooding Impacts
Rain Dominant Basins:
Possible increases in flooding due to increased precipitation
variability, but no significant change from warming alone.
Mixed Rain and Snow Basins Along the Coast:
Strong increases due to warming and increased precipitation
variability (both effects increase flood risk)
Inland Snowmelt Dominant Basins:
Relatively small overall changes because effects of warming
(decreased risks) and increased precipitation variability
(increased risks) are in the opposite directions.
Landscape Scale
Ecosystem Impacts
Annual area (ha × 106) affected by MPB in BC
9.0
2005
Bark Beetle Outbreak in British Columbia
8.0
2004
7.0
6.0
5.0
2003
4.0
3.0
2.0
2002
1.0
2001
2000
1999
0
1910 1930 1950 1970 1990 2010
Year
(Figure courtesy Allen Carroll)
Temperature thresholds for
coldwater fish in freshwater
• Warming temperatures will increasingly stress coldwater
fish in the warmest parts of our region
– A monthly average 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
Wide-Spread Glacial Retreat has Accompanied 20th
Century Warming.
Loss of glacial mass may increase summer flow in the short
term and decrease summer flow in the long term.
1902
2002
The recession of the Illecillewaet Glacier at Rogers Pass between 1902 and 2002.
Photographs courtesy of the Whyte Museum of the Canadian Rockies & Dr. Henry
Vaux.
Impact Pathways Associated with Climate
•Changes in water quantity and timing
Reductions in summer flow and water supply
Increases in drought frequency and severity
Changes in hydrologic extremes
Changing flood risk (up or down)
Summer low flows
Changes in groundwater supplies
•Changes in water quality
Increasing water temperature
Changes in sediment loading (up or down)
Changes in nutrient loadings (up or down)
•Changes in land cover via disturbance
Forest fire
Insects
Disease
Invasive species
Impact Pathways Associated with Climate
•Changes in water management practice
Hydropower production (energy demand)
Flood control operations (changing flood risk and refill
statistics)
Instream flow augmentation
Use of storage to control water temperature
•Changes in Ecosystem Protection and Recovery
Planning
Design of fish and wildlife recovery plans
Habitat restoration efforts
ESA listings (as a process)
Monitoring programs
Approaches to Adaptation and Planning
•Anticipate changes. Accept that the future climate will be
substantially different than the past.
•Use scenario based planning to evaluate options rather
than the historic record.
•Expect surprises and plan for flexibility and robustness in
the face of uncertain changes rather than counting on one
approach.
•Plan for the long haul. Where possible, make adaptive
responses and agreements “self tending” to avoid repetitive
costs of intervention as impacts increase over time.
Example of a Flexible, Self-Tending Reservoir
Operating System
•Improved Streamflow Forecasts Incorporating Warming and
Other Features of Altered Climate System
•Dynamic Reservoir Operating Systems Using Optimization or
Hybrid Optimization/Simulation Approaches to Rebalance the
Management System.
•Such systems are more flexible and adaptable because they do not
require a “trigger” for a change in the operating policies, and arguably do
not require as much intervention as the climate system gradually changes,
because the system responds autonomously to improvements in forecasts
(whether related to climate change or other scientific advances)
•These ideas are not really new:
Harvard Water Program ~1965