Transcript Sensitivity of Snow-Dominated Hydrologic Regimes to Global

Sensitivity of Snow-Dominated
Hydrologic Regimes to Global
Warming
Dennis P. Lettenmaier1, Jennifer C. Adam1, Tim P. Barnett2
1.
Dept. of Civil and Environmental Engineering, University of Washington
2. Climate Research Division, Scripps Inst. of Oceanography
European Geosciences Union
General Assembly 2006
Thursday, April 6
Vienna, Austria
1. Background
• “On a global scale, the largest changes in the
hydrological cycle due to warming are predicted for the
snow-dominated basins of mid- to higher latitudes …”
(Barnett et al, 2005)
• Approximately one-sixth of the world’s population lives in
river basins that are strongly affected by snowmelt, and
for which reservoir storage is unable to substantially
attenuate seasonal shifts in runoff.
• This region accounts for roughly one-quarter of the
global gross domestic product.
• Reduction of snow affected area can roughly be
estimated on the basis of movement of the snowline
(lower boundary of transient rain-on-snow zone) by the
psuedo-adiabatic lapse rate, or roughly 6 oC/km.
Typical hydrographs of snow, transient (rain and snow)
and rain dominated watersheds in northwestern U.S.
Map of Snowmelt-Dominated Regions
Legend
{Snowfall÷Runoff ≥ 50%} –
{Basins with large storage}
Basins with ≥ 50% Runoff
Derived from SnowmeltDominated Regions
Population
• includes approximately one-sixth of the global population
Gross Domestic Product
• includes roughly one-quarter of global GDP
Mechanisms for shift in seasonal
hydrographs in a warming climate
Warming
Earlier
Onset of
Snowmelt
Less Storage
of Water in
Snow pack
(snow
rain)
Earlier
Peak
Runoff
Reduction in
Peak Runoff
Reduced Surface
Water Availability
During
Summer/Autumn
(seasons of peak
demand)
Mountainous Regions
• snowmelt dominated regions occupy regions pole-ward of 45°
• exceptions include mountainous areas (lower latitudes) and
areas warmed by ocean waters (higher latitudes)
2. Observational evidence
As the West warms,
winter flows rise
and summer flows
drop
I.T. Stewart, D.R. Cayan, M.D.
Dettinger, 2004, Changes toward
earlier streamflow timing across
western North America, J. Climate
(in review)
Figure courtesy of Iris
Stewart, Scripps Inst. of
Oceanog. (UC San Diego)
Trends in fraction of annual runoff 1947-2003 (cells > 50 mm of SWE on April 1)
March
Relative Trend (% per year)
Figure courtesy of Alan Hamlet, U. Washington
June
3. Hydrologic implications of
climate change globally
Global Climate Change
Selected Basins
90
-150 -120 -90
-60 -30
0
30
1
60
60
0
120 150
5
4
2
30
90
7
9
6
8
90
60
30
0
3
-30
-30
-60
-60
-90
-150 -120 -90
1
2
3
4
5
-60 -30
MacKenzie
Mississippi
Amazon
Severnaya Dvina
Yenisei
0
30
60
90
6
7
8
9
120 150
-90
Amur
Yellow
Xi
Mekong
from Nijssen et al, Climatic
Change, 2001
Runoff Sensitivity
Season in which change was experienced
Change in Runoff as a result of change in Precipitation
Mackenzie
Yenisei
Severnaya Dvina
Amur
Mississippi
Yellow
Mekong
Xi
Amazon
SON
JJA
MAM
DJF
SON
JJA
MAM
DJF
SON
JJA
MAM
DJF
DJF
MAM
JJA
SON
DJF
MAM
JJA
SON
DJF
MAM
JJA
SON
Season in which change was imposed
-5%
-10%
+5%
+10%
from Nijssen et al,
Climatic Change, 2001
Runoff Sensitivity
Season in which change was experienced
Change in Runoff as a result of change in Temperature
Mackenzie
Yenisei
Severnaya Dvina
Amur
Mississippi
Yellow
Mekong
Xi
Amazon
SON
JJA
MAM
DJF
SON
JJA
MAM
DJF
SON
JJA
MAM
DJF
DJF
MAM
JJA
SON
DJF
MAM
JJA
SON
DJF
MAM
JJA
SON
Season in which change was imposed
-5%
-10%
+5%
+10%
from Nijssen et al,
Climatic Change, 2001
4. Western U.S. impact studies
Diminishing Sierra Snowpack
% Remaining, Relative to 1961-1990
Total snow losses by the
end of the century:
29–73% for the lower
emissions scenario
(3-7 MAF)
73–89% for higher
emissions (7-9 MAF – 2
Lake Shastas)
Dramatic losses under
both scenarios
Almost all snow gone by
April 1 north of Yosemite
under higher emissions
Visual courtesy
Ed Maurer
Future Spring Snowpack Remaining
by Elevation as a % of 1961-1990 levels
Losses greatest below 3,000 m: 37–79% for B1 81–94% for A1fi.
Below 1800 m (~6000 ft) >80% April 1 snow loss under all simulations
Below 2600 m (8500 ft) >75% loss for 3 of 4 simulations, both of high
emissions scenarios
Visual courtesy Ed Maurer
Impacts on Ski Season
Warmer temperatures result in:
• Less precipitation falling as
snow in winter
• Earlier melt of accumulated
snow
These combine to shorten the
ski season
Photo: SwissRe
Visual courtesy
Ed Maurer
Length of Ski Season
•
•
•
•
28-41 days (4-6 weeks) shorter for B1 scenario
39-44 days (6 weeks) shorter for A1fi
Retreat of season start: 5-14 days (losing end of November and early
December)
This is at midpoint year of 2035 – in our lifetimes.
Visual courtesy
Ed Maurer
Length of Ski Season
Minimum ski conditions never attained
•49-106 days (7-15 week) shorter for B1 scenario
•103 days shorter (15 week) to zero day ski season for A1fi
•Retreat of season start: at least 22 days
•This is at midpoint year of 2085 – in our childrens’ and grandchildrens’ lifetimes.
5. Water resources implications in the
western U.S.: The Accelerated Climate
Prediction Initiative (see Climatic
Change special issue, Jan-Feb. 2004, for
details)
BAU 3-run average
historical (1950-99)
control (2000-2048)
PCM
Business-as-Usual
scenarios
Columbia River Basin
(Basin Averages)
Percent of Control Run Climate
2040-2069
140
120
PCM Control Climate and
Current Operations
100
PCM Projected Climate
and Current Operations
PCM Projected Climate
with Adaptive Management
80
60
Firm
Hydropower
Annual Flow
Deficit at
McNary
BAU 3-run average
historical (1950-99)
control (2000-2048)
PCM
Business-as-Usual
scenarios
California
(Basin Average)
PCM
Business-as-Usual Scenarios
Snowpack Changes
California
April 1 SWE
Central Valley Water Year Type Occurrence
Percent Given WY Type
0.6
hist (1906-2000)
0.5
2020s
2050s
2090s
0.4
0.3
0.2
0.1
0.0
Critically Dry
Dry
Below Normal
Water Year Type
Above Normal
Wet
Current Climate vs. Projected
Climate
Storage Decreases
• Sacramento
Range: 5 - 10 %
Mean: 8 %
• San Joaquin
Range: 7 - 14 %
Mean: 11 %
Current Climate vs. Projected
Climate
Hydropower Losses
Central Valley Hydropower Production
1400000
• Central Valley
Range: 3 - 18 %
Mean: 9 %
• Sacramento System
Range: 3 – 19 %
Mean: 9%
• San Joaquin System
Range: 16 – 63 %
Mean: 28%
Ctrl mean
2000-2019
2020-2039
2040-2059
2060-2079
2080-2098
1200000
Megawatt-Hours
1000000
800000
600000
400000
200000
ct
O
ov
N
D
ec
Ja
n
b
Fe
M
ar
pr
A
M
ay
n
Ju
l
Ju
ug
A
p
Se
PCM Projected Colorado R.
Temperature
Timeseries
Average
Annual
ctrl.
avg.
hist. avg.
Period 1 2010-2039
Period 2 2040-2069
2098
Period 3 2070-
PCM Projected Colorado R.
Precipitation
Timeseries
Average
Annual
hist. avg.
ctrl.
avg.
Period 1 2010-2039
Period 2 2040-2069
2098
Period 3 2070-
Annual Average Hydrograph
Simulated Historic (1950-1999) Period 1 (2010-2039)
Control (static 1995 climate)
Period 2
(2040-2069)
Period 3 (2070-2098)
Total Basin Storage
Figure 8
70
Minimum
60
Average
Maximum
Storage, BCM
50
40
30
20
10
0
Historical
Control
Period 1
Period 2
Period 3
Annual Releases to the Lower
Basin
Figure 9
14
1.2
Average Annual Release to Lower Basin (BCM/YR)
Probability release to Lower Basin meets or exceeds target (probability)
12
1
target
release
10
8
0.6
6
0.4
4
0.2
2
0
0
Historical
Control
Period 1
Period 2
Period 3
Probability
BCM / YR.
0.8
Annual Releases to Mexico
Figure 10
1.2
Average Annual Release to Mexico
(BCM/YR)
3
Probability release to Mexico meets or
exceeds target (probability)
BCM / YR.
2.5
2
target
release
1.5
1
0.8
0.6
0.4
1
0.2
0.5
0
0
Historical
Control
Period 1
Period 2
Period 3
Probability
3.5
Figure 12
Annual Hydropower
Production
18000
Minimum
16000
Average
Energy, GW - hr
14000
Maximum
12000
10000
8000
6000
4000
2000
0
Historical
Control
Period 1
Period 2
Period 3
Summary of ACPI results
• Columbia and California reservoir systems primarily provide
within-year storage (total storage/mean flow ~ 0.3 – 0.5),
whereas Colorado is an over-year system (~4)
• Climate sensitivities in Columbia basin and California are
dominated by seasonality shifts in streamflow, and may even be
beneficial for hydropower. However, fish flow targets would be
difficult to meet under altered climate, and mitigation by altered
operation is essentially impossible.
• California system operation is dominated by water supply
(mostly ag), reliability of which would be reduced significantly by
a combination of seaonality shifts and reduced (annual)
volumes. Partial mitigation by altered operations is possible, but
complicated by flood issues.
• Colorado system is sensitive primarily to annual streamflow
volumes. Low runoff ratio makes the system highly sensitive to
modest changes in precipitation (in winter, esp, in headwaters);
temperature changes are much less important.
Conclusions
• Impacts of climate change on the hydrology of
snowmelt dominated rivers (of which
mountainous watersheds are a particularly
important subset) are among the most
predictable impacts of climate change
• Transient snow domains are most “at risk”, but
impacts will be felt in all ephemeral snow
domains
• Changes over the last century are detectable,
and have already impacted the reliability of
water supply systems in the western U.S.
• Planning methods that incorporate ongoing and
future climate change are urgently needed as
operating agencies begin to recognize the
problems and issues
Rhine River
(Middelkoop et al. 2001)
Discharge, m3/s
Aare River at Brugg
H. Middelkoop et al., Impact of climate change on
hydrological regimes and water resources management in
the Rhine Basin, Clim. Change, 49: 105-128, 2001.
(Image: Ultrecht Univ., Netherlands)
Discharge, m3/s
Rhine River at Rheinfelden
Rhine River
(Middelkoop et al. 2001)
Discharge, m3/s
Rhine River at Rees
Some Implications:
• reduction of water availability during
season of peak demand
• increase in number of low-flow days
(affects ship transport)
H. Middelkoop et al., Impact of climate change on
hydrological regimes and water resources management in
the Rhine Basin, Clim. Change, 49: 105-128, 2001.
(Image: Ultrecht Univ., Netherlands)
• decrease in level of flood protection
• decrease in annual hydropower
production (some sub-basins)
Canadian Prairies (de Loë et al. 2001)
• agriculture sensitive to
drought (irrigation
derived primarily from
surface waters)
• predictions include:
decrease in snow-pack,
earlier peak runoff, and
lower summer soil
moistures
R. de Loë et al., Adaptation options for the near term:
climate change and the Canadian water sector, Global Env.
Change, 11, 231-245, 2001.
• implications: agriculture
more at risk in a warming
climate; and heightened
competition with other
water needs (aquatic
habitat and down-stream
requirements)
Glaciers…
Recession of Grinnell
Glacier, Glacier National
Park (1911 and 2000)