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)