ClimateVariabilityClimate

Variability

Climate Impacts Group&

Department of Atmospheric SciencesUniversity of Washington

Eric Salathé

Thanks to Nathan Mantua

Northwest Climate: the mean

Factors that influence local/regional climate:

1. Latitude

• day length, intensity of sunlight

2. Altitude

3. Mountain Barriers

4. Proximity to the ocean

• ocean currents

5. location relative to prevailing winds

Mean SLP fields

• the dominant feature shifts from the subtropical High in summer to the Aleutian Low in winter

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Oregon Climate Servicehttp://www.ocs.orst.edu

Northwest terrain maps the big-picture windsand storms onto a complex landscape

• localized cold air outbreaks

• the Puget Sound Convergence Zone

• rain shadows

“Arctic Blasts”

The Puget Sound Convergence Zone

Annual average rain+snowfall: 1961-1990

The predictable part: seasonal rhythms

Puget Sound Precip

Upwelling winds at 48N

Amphitrite Pt SST

Oct Feb Jun

Oct Feb Jun

Oct Feb Jun Jan May Sep

InsolationInsolation

Year to year variations on the seasonal rhythms

Monthly Puget Sound Precip

Daily Upwelling winds

Monthly Amphitrite Pt SST

Northwest Climate Variability

Pollen records on the Olympic Peninsula

Crocker Lake

McLachlan, J. S. and L. B. Brubaker. 1995 Local and regional vegetation change on the northeastern Olympic Peninsula during the Holocene. Canadian J. of Botany.

alder

cedars

pines

df

cool

fires: hot-dry

cool-wet

1750 1775 1800 1825 1850 1875 1900 1925 1950 1975 2000Year

5.0

5.1

5.2

5.3

5.4

5.5

Log10 mean flow, The Dalles, OR (cfs)

Source: Gedalof, Z., D.L. Peterson and Nathan J. Mantua. (2004). Columbia River Flow and Drought Since 1750. Journal of the American

Water Resources Association.

The Dust Bowl (1929-1931) was probably not the worst drought sequence in the past 250 years

(based on Columbia Basin Tree-ring chronologies)(based on Columbia Basin Tree-ring chronologies)

red = observed, blue = reconstructed

PNW climate variability

1. What does our region’s climate history tell us about “natural variability”?

2. How is climate variability experienced in the Pacific Northwest? * are there patterns within the region? * are there preferred frequencies of change (year to year, decade to decade, etc.)

3. Why does our climate vary?

Warm and cool (or “wet” and “dry”) halves of the year: oct-mar versus apr-sep

Characteristics of variability?

• Lots of year-to-year variability in both halves of the year; longer-term variations– Multi-decadal “cycles” and century long trends

• temperatures and precipitation are more variable in cool season than in warm season

Washington State Oct-Sept Total Precip

36

48

19871967194719271907 2007

Washington State Oct-Sept Average Temperature

46

48

19871967194719271907 2007

50

Riffe Lake, west slopes of the Cascades

Spring 2001

March 15 Snow depth anomalies at Paradise, Mt Rainier

Avg ~ 4 meters (170 inches)January 5, 2005: 48 inchesJanuary 6, 2007: 130 inches

Avg=4 meters

Water Year Columbia River streamflow

Average annual runoff at The Dalles, Oregon ~ 150 Million Acre-Feet (MAF);

Oct 2000-September 2001 ~ 100 MAF

NW Climate variability

• Why the strong climate changes?– The chaotic nature of the climate system– big volcanic eruptions– natural modes of climate variability internal to

the climate system: • in the Pacific sector, changes in ENSO and PDO

are important factors

• Circulation changes are sensitive to the intensity of tropical El Nino events

• Contrast the “average” event with the extreme winters of 1982-83 and 1997-98

Oct 97-Mar 98:El Niño

Oct 98-Mar 99:La Niña

El Niño year precip anomalies Oct 1997- Mar 1998

La Niña year precip anomalies Oct 1998- Mar 1999

Regional patterns?

• Typically, cool-season (oct-mar) climate anomalies are coherent throughout most of the PNW region

• warm-season climate anomalies also tend to be regionally coherent, but to a lesser degree

Regional patterns?

Observations Regional Simulation

Leung et al 2003

Dry

wet

Accumulated daily rainfall: Oct 1 1998-Sept 20 1999 A very wet year everywhere but Yakima!

http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/ensostuff/current_impacts/global_precip_accum.html

“composite avg” PNW temperature and precipitation

during El Niño and La Niña

(based on averages of past century’s events)

EN-LN

The Pacific Decadal Oscillation

• an El Niño-like pattern of climate variability

• 20 to 30 year periods of persistence in North American and Pacific Basin climate

• warm extremes prevailed from 1925-46, and again from 1977-98; a prologed cold era spanned 1947-76

1998?1925 1947 1977

Mantua et al. 1997, BAMS

Figures produced by Todd Mitchell, UW/JISAO

October-March PDO Regression fieldsOctober-March PDO Regression fieldsMaps show typical warm PDO climate anomaliesMaps show typical warm PDO climate anomalies

Surface Air Temperature Precipitation

Strong Strong

Aleutian Aleutian

LowLow

Strong Strong

Aleutian Aleutian

LowLow

Warm

Warm

drydry

drydry

wetwet

drydry

drydry

A history of ENSO

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

warm coolwarm

A history of the PDO

Real time “nowcasts” of the PDO?

http://jisao.washington.edu/pdo

Monthly PDO index: 1900-Jan 2008

Because we don’t know how the PDO works (key mechanisms for decadal patterns remain mysterious), we can’t be sure that the SST pattern (and PDO index) is a good indicator for where we are with this pattern. Recent years have a variable PDO index…but perhaps no moreso than the late 1980s…

PDO and PNW monthly temperatures and precipitation

PDO and Cascades snowpack

0

100000

200000

300000

400000

500000

600000

700000

Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep

Month

Average Flow (cfs)

ColdPDO

WarmPDO

Water year stream flow composites for Columbia River “natural” flows at The Dalles, Oregon

PDO/ENSO and NW hydrology

• Because extremes in ENSO and PDO tend to favor either “warm and wet” or “cool and dry” conditions, these combinations lead to amplified responses in snowpack and streamflow – Ex: cold wet weather, lower snowline, more

precipitation, more snow, less evaporation and more runoff

Cool/Warm PDO and Paradise snowdepth histograms

From the National Climate Data Center: www.ncdc.noaa.gov

1977

19941944

October-March OR-ID-WA Temperature and Precipitation

*

A regionally averaged view of PNW cool season Temps and precip

Major drought years

2001

Winter windsand pressure over the North Pacific

Summer windsand pressure over the North Pacific

“Aleutian Low” “Subtropical High”

HH

LL