selected presentation from the instaar monday noon seminar...

Selected Presentation from the INSTAAR Monday Noon Seminar Series.

Institute of Arctic and Alpine Research, University of Colorado at Boulder.http://instaar.colorado.edu

http://instaar.colorado.edu/other/seminar_mon_presentations

This seminar presentation has been posted to the internet to foster communication with the science community and thepublic.

Most of the INSTAAR presentations were originally given in PowerPoint format; they were converted to Adobe PDF forposting. You may need to install the free Adobe Acrobat Reader to view these files.

These presentations are "works in progress". They are not peer reviewed. They should not be referenced for any kind ofpublication. Contact the author for proper references and additional information before any use, even for unpublishedworks such as your own presentations.

LICENSING AGREEMENT.Free use of these presentations is limited to a nonprofit educational or private non-commercial context and requires thatyou contact the author, give credit to the author, and display the copyright notice. All rights to reproduce thesepresentations are retained by the copyright owner. Images remain the property of the copyright holder. By accessingthese presentations, you are consenting to our licensing agreement.

07 Oct. 2002 Tim Kittel et al., National Center for Atmospheric Research, INSTAAR affiliate, Email: [email protected]"Historical and Future Climates of the Rocky Mountains".Seminar given at INSTAAR, University of Colorado. Copyright 2002 Tim Kittel. All Rights Reserved.Kittel presentation (0.5 Mb PDF).

T. Kittel INSTAAR Seminar 7 Oct

2002

HISTORICAL AND FUTURE CLIMATESHISTORICAL AND FUTURE CLIMATES

OF THE US ROCKY MOUNTAINSOF THE US ROCKY MOUNTAINS

Timothy Kittel

INSTAAR Affiliate

University of Colorado, Boulder

with: J. Andy Royle, USFWS

Peter Thornton, Nan Rosenbloom, & Steve Aulenbach, NCAR

Tom Chase, CIRES and Dept of Geography, CU

T. Kittel INSTAAR Seminar 7 Oct 2002

+ Citations for presented research are:

• Kittel, T.G.F., P.E. Thornton, J.A. Royle, and T.N. Chase. 2002.Climates of the Rocky Mountains: Historical and Future Patterns.Pages 59-82 (Chapter 4), in: J.S. Baron (ed.). Rocky MountainFutures: An Ecological Perspective. Island Press, Covelo, CA. 325 p.

• Kittel, T.G.F. and J.A. Royle. 100-year climate history of the U.S.Rocky Mountains. J. Climate, in preparation.

+ Contact information:

• [email protected] 303 258-0908

+ Original graphics and tables not published in Baron 2002 are copyright © 2002 T. Kittel.

All rights reserved.


THE ROCKY MOUNTAINS

+ Geographic context• Societal• Hydrological• Ecological

+ Spatially extensive –• 35-65°N

• warm temperate ‡ boreal

+ Source for great river systems

D. Cairns in Baron 2002


GEOGRAPHY OF BIOGEOCHEMICAL PROCESSES

The Mountain West:

+ Positive net ecosystemexchange (C sequestration)

+ Net exchange sensitive toclimate variability anddirectional change

Schimel et al. 2002. Eos

ANNUAL NET ECOSYSTEM EXCHANGE (NEE)

Biome-BGC simulated NEE draped over topography

VEMAP Climate 1980-1989


OBJECTIVES

+ Are there significant historical temporal patterns in climate –trends and interannual variability – across the US Rockies?

+ Are there lessons from a retrospective – and from climatemodels – that can be applied to understanding effects ofcontinued altered forcing on high elevation climates?


HISTORICAL ANALYSIS

+ US Rockies

• 3 regions

+ 1895-1993

• 79 long-record stations

• US HCN and coop stns (NCDC)

• Statistical in-filling

• Moving-window kriging model(Kittel et al. in review)

+ Variables

• Tmin Tmax

• Diurnal temperature range (DTR)

• Precipitation

NORTHERN

CENTRAL

SOUTHERN

Long-Record Climate Station

500m contours

US ROCKY MOUNTAINS


SPECIFIC QUESTIONS

+ What is the character of climate variability in the Rockies?

• Does this variability (and its teleconnections) depend on:• Region

• Elevation

+ Are there significant trends in temperature and precipitation inthe historical record?

• Do these trends depend on:• Region

• Elevation


ARE THERE 20th CENTURY TRENDS?

+ Temperature

• Significant T trendstend to be >0

• Tmin (+0.5 - +1.0°C/100y)

> Tmax

• Diurnal T Rangetrends <0

+ Precipitation

• Significant trendstend to be >0

PPT Trend = 30%/100y (p<0.05)

DTR Trend = -0.6°C/100y (p<0.05)


DO TRENDS DIFFER BY REGION? – PPT

+ Regional differences vary withseason

Precipitation Trend (%/100y)

5%-5%SOUTH

30%*3%NORTH

*p<0.05

33%*2%CENTRAL

SUMMERWINTER


DO TRENDS DIFFER BY REGION? – DTR

+ Regional differences followcontinental pattern

• Strongest DTR decreases in mid-latitudeNAmer, weakening poleward(Easterling et al. 1997)

• Due to increased cloud cover(Dai et al. 1999)

• Consistent with increasing ppt

Diurnal T Range Trend (°C/100y)

+0.2-0.2SOUTH

-0.6*-0.6*NORTH

*p<0.05 **p<0.005

-1.2**-0.5CENTRAL

SUMMERWINTER


+ PPT trends f (elevation)

• Reduction or amplificationof lowland signal

> Strong trends at oneelevation zone

• Trend sign switching withelevation

> Decoupling

+ Seasonal dependence

• Elevation effect switchingwith season

DO TRENDS VARY WITH ELEVATION? – PPT

NORTHERN

0

1000

2000

3000

4000

-5 -4 -3 -2 -1 0 1 2 3 4 5

Precipitation Trend (cm/100y)

Ele

va

tio

n (

m)

Fall

Winter Summer

Spring

,, ::

p<0.01

n.s.


+ Significant changes in trends with elevation> trends in lapse rate

+ Sign switching with elevation

+ Diurnal dependence

Tmax NORTHERN

0

1000

2000

3000

4000

-5 -4 -3 -2 -1 0 1 2 3 4 5

Temperature Trend (C/100y)E

lev

ati

on

(m

)

Tmin NORTHERN

0

1000

2000

3000

4000

-5 -4 -3 -2 -1 0 1 2 3 4 5

Temperature Trend (C/100y)

Ele

va

tio

n (

m) Winter

Spring

Summer

Fall

p<0.05

n.s.

TRENDS vs. ELEVATIONTmin and Tmax


TRENDS vs. ELEVATION? –

Diurnal Temperature Range

+ Diurnal T Range trend elevation dependent

NORTHERN

0

1000

2000

3000

4000

-5 -4 -3 -2 -1 0 1 2 3 4 5

DTR Trend (C/100y)

Ele

va

tio

n (

m) Winter

Spring

Summer

Fall

SOUTHERN

0

1000

2000

3000

4000

-5 -4 -3 -2 -1 0 1 2 3 4 5

DTR Trend (C/100y)

+

+ Region dependent

p<0.05

n.s.


AN ELEVATION EFFECT?

+ Higher reaches of mountain systems in closer contact with free troposphere

• Respond rapidly to upper-air changes (Greenland and Losleben 2001)

• Less affected by ameliorating surface processes (Giorgi et al. 1997)

+ Upper air overrides lower air in presence of inversions

• Widely differing air mass sources

• Decoupled from lower-level convective mixing, valley fogs (Beniston and Rebetez 1996, Diaz and Bradley 1997)

+ Snow-albedo feedback

• Amplification of regional temperature signal –

• Years with regionally higher temperatures have less snowcover at elevation

>more absorption of solar radiation

>greater high elevation warming (Giorgi et al. 1997)


INTERANNUAL VARIABILITY

– SIMILAR ACROSS REGIONS? –

+ Adjacent regions more strongly correlated

+ Cross-correlations similar by season

CROSS-CORRELATION

-

0.8*

0.6*

SOUTH

Annual PPT Annual Tmin

0.4*0.2SOUTH

0.9* -NORTH

*p<0.01

-0.6*CENTRAL

CENTRALNORTH


TELECONNECTIONS?

+ Teleconnections with:

• North Pacific SST and Lows (NPI)

• El Niño/Southern Oscillation (SOI)

modified from Mitchell 1976

Bash, in Benedict 1991

GENERAL ATMOSPHERIC CIRCULATION

+ Drivers of regional patterns in meanclimate

+ Indicators of sources ofinterannual climate variability


TELECONNECTIONS

+ Southern Oscillation Index (SOI)

• Associated with El Niño

• Negative SOI = Warm SST phase(El Niño)

• Positive SOI = Cold phase

SOI

NPI+ Northern Pacific Index (NPI)

• Aleutian Low Pressure System

• Negative NPI = Deep Low ‡Blocking, meridional flow

• Positive NPI = Weak Low ‡ Zonalflow

• Pacific Decadal Oscillation

Trenberth and Hurrell


ARE THERE TELECONNECTIONS?

+ Negative NPI corresponds todeeper Aleutian Low

• Negative coefficient > warmerwinter with deeper Low

• Stronger circulation around Low> more southerly flow (warmerair) into the US Rockies inwinter

+ Gradient in teleconnectionstrength: S ‡ N

WINTER Tmin

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

Circulation Index

Re

gre

ss

ion

Co

eff

icie

nt

NPI

SOI

North

Central

South

* p<0.05

**p<0.005

*

** **


SUMMER PPT

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

NPI SOI

Circulation Index

** ** **

SUMMER

+ Negative NPI > Stronger Low

• More ppt in North

+ Negative SOI > Warm phase

• More ppt in the South & Central

TELECONNECTIONS– Vary along N-S Gradient and by Season –

WINTER

+ Positive NPI > Zonal flow

• More storm tracks into mid-lats

+ Negative SOI > Warm phase

• More ppt in the South

WINTER PPT

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

NPI SOI

Circulation Index

Reg

ressio

n C

oeff

icie

nt

North

Central

South

* p<0.05

**p<0.005

*

**


DO TELECONNECTIONS

VARY WITH ELEVATION?

+ Relative importance ofcirculation index changes withelevation

+ Behavior dependent on regionand season

SOUTHERN ROCKIES

SOI

ELEVATION (m)

CO

RR

ELA

TIO

N

0

NPI

JULY PPT- Circ Correlation

CO

RR

ELA

TIO

N

0

p<0.01

p<0.05


THE FUTURE?

+ Multiple Forcings

• Increasing greenhouse gases

• Landuse change, regional andglobal

+ Regional sensitivity to alteredGHGs and sulfate aerosols

• Comparable for landuse change(Chase et al. 2001)

Annual PPT

Summer PDSI

Winter DTR

HAD

CCC

NORTH

CENTRAL

SOUTH

Palmer Drought Severity Index

Palmer Drought Severity Index

Palmer Drought Se i t Index

Historical Future Simulated


SURFACE RESPONSES TO REGIONAL FORCING

Coupled Climate Model Experiment – Increasing GHG+Sulfate Aerosols

Snowfree period calculated with Biome-BGC (P. Thornton, in Kittel et al. 2002)

+ Broad extraregionally forced changes result in finer scaled responses

CCC Climate


+ Elevation effect

+ Region dependent

+ Climate model experiment dependent

SURFACE RESPONSES TO REGIONAL FORCING –

ELEVATIONAL DEPENDENT?

NORTH

D SNOW-FREE PERIOD D SUMMER PDSI

Change in PDSI Change in Snow-free Period (months)

ELE

VATIO

N (

m)

ELE

VATIO

N (

m)

p<0.005p<0.001

p<0.001p<0.001

CENTRAL


SUMMARY

HISTORICAL TRENDS

+ Significant, generally positive 20th century regional trends in PPT, Tmin,and Tmax

• Tmin trends > Tmax trends – Diurnal T Range narrowed

• Differed by region – larger in North and Central

+ Trends varied with elevation

• High elevation trends were amplified, reduced, or opposite from lowerelevation

• No consistent pattern with season or region


SUMMARY

INTERANNUAL VARIABILITY

+ Interannual variability in PPT, Tmin, and Tmax was regional in nature

• Adjacent regions more strongly correlated

+ Significant teleconnections with global atmospheric circulation patterns

• Regional dependence: NPI influence stronger in north, SOI in South

• Strength and/or sign of relationship can depend on season

• Depend elevation


SUMMARY

FUTURE PATTERNS?

+ Extraregional forcing from altered atmospheric composition, land coverchange

+ Strong, complex regional and elevation dependent reworking of thisforcing by mountain climatic processes – atmospheric, hydrological, andecological

• Amplification or reduction of lowland signal, or decoupling


Further reading:

Kittel, T.G.F., P.E. Thornton, J.A. Royle, and T.N.Chase. 2002. Climates of the Rocky Mountains:Historical and Future Patterns. Pages 59-82(Chapter 4), in: J.S. Baron (ed.). Rocky MountainFutures: An Ecological Perspective. Island Press,Covelo, CA. http://www.islandpress.com

selected presentation from the instaar monday noon seminar...

Documents