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Sensitivity of Snow-Dominated Hydrologic Regimes to Global Warming. Dennis P. Lettenmaier 1 , Jennifer C. Adam 1 , Tim P. Barnett 2 Dept. of Civil and Environmental Engineering, University of Washington Climate Research Division, Scripps Inst. of Oceanography. European Geosciences Union - PowerPoint PPT Presentation
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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 Washington2. Climate Research Division, Scripps Inst. of Oceanography
European Geosciences UnionGeneral Assembly 2006
Thursday, April 6Vienna, 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
{Snowfall÷Runoff ≥ 50%} –{Basins with large storage}
Basins with ≥ 50% Runoff Derived from Snowmelt-Dominated Regions
Legend
Population
• includes approximately one-sixth of the global population
Gross Domestic Product
• includes roughly one-quarter of global GDP
Less Storage of Water in Snow pack
(snow rain)
Warming
Earlier Onset of
Snowmelt
Earlier Peak
Runoff
Reduction in Peak Runoff
Reduced Surface Water
Availability During
Summer/Autumn (seasons of peak
demand)
Mechanisms for shift in seasonal hydrographs in a warming climate
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)
March June
Relative Trend (% per year)
Trends in fraction of annual runoff 1947-2003 (cells > 50 mm of SWE on April 1)
Figure courtesy of Alan Hamlet, U. Washington
3. Hydrologic implications of climate change globally
Global Climate ChangeSelected Basins
1 MacKenzie2 Mississippi3 Amazon
4 Severnaya Dvina5 Yenisei
6 Amur7 Yellow8 Xi9 Mekong
-90
-60
-30
0
30
60
90
-90
-60
-30
0
30
60
90
-150 -120 -90 -60 -30 0 30 60 90 120 150
-150 -120 -90 -60 -30 0 30 60 90 120 150
1
2
3
4 56
789
from Nijssen et al, Climatic Change, 2001
Mackenzie
DJF
MAM
JJA
SON
Yenisei Severnaya Dvina
Amur
DJF
MAM
JJA
SON
Mississippi Yellow
Mekong
DJF MAM JJA SON
DJF
MAM
JJA
SON
Xi
DJF MAM JJA SON
Amazon
DJF MAM JJA SON
Season
in
wh
ich
ch
an
ge w
as e
xp
eri
en
ced
Season in which change was imposed
-5% -10% +5% +10%
Runoff SensitivityChange in Runoff as a result of change in Precipitation
from Nijssen et al, Climatic Change, 2001
Runoff SensitivityChange in Runoff as a result of change in Temperature
Mackenzie
DJF
MAM
JJA
SON
Yenisei Severnaya Dvina
Amur
DJF
MAM
JJA
SON
Mississippi Yellow
Mekong
DJF MAM JJA SONDJF
MAM
JJA
SON
Xi
DJF MAM JJA SON
Amazon
DJF MAM JJA SON
Season
in
wh
ich
ch
an
ge w
as e
xp
eri
en
ced
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 Remainingby 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 simulationsBelow 2600 m (8500 ft) >75% loss for 3 of 4 simulations, both of high emissions scenarios
Visual courtesy Ed Maurer
Impacts on Ski SeasonWarmer 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
•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.
Minimum ski conditions never attained
5. Water resources implications in the western U.S.: The Accelerated Climate Prediction Initiative (see Climatic Change special issue, Jan-Feb. 2004, for details)
PCM Business-as-Usual scenarios
Columbia River Basin(Basin Averages)
control (2000-2048)
historical (1950-99)
BAU 3-run average
2040-2069
60
80
100
120
140
FirmHydropower
Annual FlowDeficit atMcNary
Pe
rce
nt
of
Co
ntr
ol
Ru
n C
lim
ate
PCM Control Climate andCurrent Operations
PCM Projected Climateand Current Operations
PCM Projected Climatewith Adaptive Management
PCM Business-as-Usual scenarios
California(Basin Average)
control (2000-2048)
historical (1950-99)
BAU 3-run average
PCM Business-as-Usual Scenarios
Snowpack ChangesCaliforniaApril 1 SWE
Central Valley Water Year Type Occurrence
0.0
0.1
0.2
0.3
0.4
0.5
0.6
Critically Dry Dry Below Normal Above Normal Wet
Water Year Type
Per
cen
t G
iven
WY
Typ
e
hist (1906-2000) 2020s 2050s 2090s
Storage Decreases• Sacramento
Range: 5 - 10 %Mean: 8 %
• San Joaquin Range: 7 - 14 %Mean: 11 %
Current Climate vs. Projected Climate
Current Climate vs. Projected Climate
Central Valley Hydropower Production
200000
400000
600000
800000
1000000
1200000
1400000
OctNov
Dec Jan
Feb Mar Apr
May Ju
nJu
lAug
Sep
Meg
awat
t-H
ou
rs
Ctrl mean
2000-2019
2020-2039
2040-2059
2060-2079
2080-2098
Hydropower Losses• Central Valley
Range: 3 - 18 %Mean: 9 %
• Sacramento System Range: 3 – 19 %Mean: 9%
• San Joaquin System Range: 16 – 63 %Mean: 28%
Timeseries Annual Average
Period 1 2010-2039 Period 2 2040-2069 Period 3 2070-
2098
hist. avg.
ctrl. avg.
PCM Projected Colorado R. Temperature
hist. avg.
ctrl. avg.
PCM Projected Colorado R. Precipitation
Timeseries Annual Average
Period 1 2010-2039 Period 2 2040-2069 Period 3 2070-
2098
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
Annual Releases to the Lower Basin
target release
Annual Releases to Mexico
target release
Annual Hydropower Production
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)
Aare River at Brugg
Rhine River at Rheinfelden
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)
Dis
char
ge,
m3/s
Dis
char
ge,
m3/s
Rhine River (Middelkoop et al. 2001)
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)
Rhine River at Rees
Dis
char
ge,
m3/s
Some Implications:
• reduction of water availability during season of peak demand
• increase in number of low-flow days (affects ship transport)
• decrease in level of flood protection
• decrease in annual hydropower production (some sub-basins)
Canadian Prairies (de Loë et al. 2001)
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.
• agriculture sensitive to drought (irrigation derived primarily from surface waters)
• predictions include: decrease in snow-pack, earlier peak runoff, and lower summer soil moistures
• 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)
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