Selected Presentation from the INSTAAR Monday Noon Seminar Series.

Transcription

1 Selected Presentation from the INSTAAR Monday Noon Seminar Series. Institute of Arctic and Alpine Research, University of Colorado at Boulder. This seminar presentation has been posted to the internet to foster communication with the science community and the public. Most of the INSTAAR presentations were originally given in PowerPoint format; they were converted to Adobe PDF for posting. 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 They are not peer reviewed.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 of publication. Contact the author for proper references and additional information before any use, even for unpublished works such as your own presentations.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 that you contact the author, give credit to the author, and display the copyright notice. All rights to reproduce these presentations are retained by the copyright owner. Images remain the property of the copyright holder. By accessing these presentations, you are consenting to our licensing agreement. 07 Oct Tim Kittel et al., National Center for Atmospheric Research, INSTAAR affiliate, kittel@ucar.edu "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).

2 HISTORICAL AND FUTURE CLIMATES OF 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 T. Kittel of INSTAAR Geography, Seminar CU 7 Oct 2002

3 + Citations for presented research are: Kittel, T.G.F., P.E. Thornton, J.A. Royle, and T.N. Chase Climates of the Rocky Mountains: Historical and Future Patterns. Pages (Chapter 4), in: J.S. Baron (ed.). Rocky Mountain Futures: 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: kittel@ucar.edu Original graphics and tables not published in Baron 2002 are copyright 2002 T. Kittel. All rights reserved.

4 THE ROCKY MOUNTAINS + Geographic context Societal Hydrological Ecological + Spatially extensive N warm temperate boreal + Source for great river systems D. Cairns in Baron 2002

5 GEOGRAPHY OF BIOGEOCHEMICAL PROCESSES The Mountain West: ANNUAL NET ECOSYSTEM EXCHANGE (NEE) + Positive net ecosystem exchange (C sequestration) + Net exchange sensitive to climate variability and directional change Biome-BGC simulated NEE draped over topography VEMAP Climate Schimel et al Eos

6 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 climate models that can be applied to understanding effects of continued altered forcing on high elevation climates?

7 HISTORICAL ANALYSIS US ROCKY MOUNTAINS + US Rockies NORTHERN 3 regions long-record stations US HCN and coop stns (NCDC) Statistical in-filling Moving-window kriging model (Kittel et al. in review) 500m contours CENTRAL + Variables T min T max SOUTHERN Diurnal temperature range (DTR) Precipitation Long-Record Climate Station

8 SPECIFIC QUESTIONS + Are there significant trends in temperature and precipitation in the historical record? Do these trends depend on: Region Elevation + What is the character of climate variability in the Rockies? Does this variability (and its teleconnections) depend on: Region Elevation

9 ARE THERE 20 th CENTURY TRENDS? + Precipitation Significant trends tend to be >0 PPT Trend = 30%/100y (p<0.05) + Temperature Significant T trends tend to be >0 T min ( C/100y) > T max Diurnal T Range trends <0 DTR Trend = -0.6 C/100y (p<0.05)

10 DO TRENDS DIFFER BY REGION? PPT Precipitation Trend (%/100y) NORTH CENTRAL SOUTH *p<0.05 WINTER 3% 2% -5% SUMMER 30%* 33%* 5% + Regional differences vary with season

11 DO TRENDS DIFFER BY REGION? DTR Diurnal T Range Trend ( C/100y) NORTH CENTRAL SOUTH *p<0.05 WINTER -0.6* **p<0.005 SUMMER -0.6* -1.2** Regional differences follow continental pattern Strongest DTR decreases in mid-latitude NAmer, weakening poleward (Easterling et al. 1997) Due to increased cloud cover (Dai et al. 1999) Consistent with increasing ppt

12 DO TRENDS VARY WITH ELEVATION? PPT + PPT trends f (elevation) Reduction or amplification of lowland signal > Strong trends at one elevation zone Trend sign switching with elevation > Decoupling + Seasonal dependence Elevation effect switching with season Elevation (m) Winter Fall p<0.01 n.s., : NORTHERN Spring Summer Precipitation Trend (cm/100y)

13 TRENDS vs. ELEVATION T min and T max 4000 Tmin NORTHERN 4000 Tmax NORTHERN Elevation (m) p<0.05 n.s. Elevation (m) Winter Spring Summer Fall Temperature Trend (C/100y) Temperature Trend (C/100y) + Significant changes in trends with elevation > trends in lapse rate + Sign switching with elevation + Diurnal dependence

14 TRENDS vs. ELEVATION? Diurnal Temperature Range 4000 NORTHERN 4000 SOUTHERN Elevation (m) Winter Spring Summer Fall p<0.05 n.s DTR Trend (C/100y) DTR Trend (C/100y) + Diurnal T Range trend elevation dependent + Region dependent

15 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)

16 INTERANNUAL VARIABILITY SIMILAR ACROSS REGIONS? CROSS-CORRELATION Annual PPT Annual Tmin NORTH CENTRAL SOUTH NORTH - 0.9* 0.6* CENTRAL 0.6* - 0.8* SOUTH * - *p< Adjacent regions more strongly correlated + Cross-correlations similar by season

17 TELECONNECTIONS? GENERAL ATMOSPHERIC CIRCULATION + Drivers of regional patterns in mean climate + Indicators of sources of interannual climate variability Bash, in Benedict Teleconnections with: North Pacific SST and Lows (NPI) El Niño/Southern Oscillation (SOI) modified from Mitchell 1976

18 SOI TELECONNECTIONS + Southern Oscillation Index (SOI) Associated with El Niño Negative SOI = Warm SST phase (El Niño) Positive SOI = Cold phase + Northern Pacific Index (NPI) Aleutian Low Pressure System Negative NPI = Deep Low Blocking, meridional flow Positive NPI = Weak Low Zonal flow NPI Pacific Decadal Oscillation Trenberth and Hurrell

19 ARE THERE TELECONNECTIONS? + Negative NPI corresponds to deeper Aleutian Low Negative coefficient > warmer winter with deeper Low Stronger circulation around Low > more southerly flow (warmer air) into the US Rockies in winter + Gradient in teleconnection strength: S N Regression Coefficient * p<0.05 **p<0.005 ** ** NPI * WINTER Tmin SOI North Central South Circulation Index

20 TELECONNECTIONS Vary along N-S Gradient and by Season Regression Coefficient * p<0.05 **p<0.005 * NPI WINTER PPT SOI ** ** North Central South NPI SUMMER PPT ** SOI ** Circulation Index WINTER + Positive NPI > Zonal flow More storm tracks into mid-lats Circulation Index SUMMER + Negative NPI > Stronger Low More ppt in North + Negative SOI > Warm phase More ppt in the South + Negative SOI > Warm phase More ppt in the South & Central

21 DO TELECONNECTIONS VARY WITH ELEVATION? + Relative importance of circulation index changes with elevation + Behavior dependent on region and season SOUTHERN ROCKIES JULY PPT- Circ Correlation CORRELATION NPI 0 p<0.05 CORRELATION SOI p< ELEVATION (m)

22 THE FUTURE? + Multiple Forcings Increasing greenhouse gases Landuse change, regional and global + Regional sensitivity to altered GHGs and sulfate aerosols Comparable for landuse change (Chase et al. 2001) Palmer Drought Se i t Index Annual PPT NORTH Historical HAD CCC Future Simulated Palmer Drought Severity Index Winter DTR CENTRAL Palmer Drought Severity Index Summer PDSI SOUTH

23 SURFACE RESPONSES TO REGIONAL FORCING Coupled Climate Model Experiment Increasing GHG+Sulfate Aerosols CCC Climate Snowfree period calculated with Biome-BGC (P. Thornton, in Kittel et al. 2002) + Broad extraregionally forced changes result in finer scaled responses

24 SURFACE RESPONSES TO REGIONAL FORCING ELEVATIONAL DEPENDENT? D SNOW-FREE PERIOD NORTH D SUMMER PDSI ELEVATION (m) p<0.005 p<0.001 ELEVATION (m) p<0.001 CENTRAL p<0.001 Change in Snow-free Period (months) Change in PDSI + Elevation effect + Region dependent + Climate model experiment dependent

25 HISTORICAL TRENDS SUMMARY + Significant, generally positive 20 th century regional trends in PPT, T min, and T max T min trends > T max 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 lower elevation No consistent pattern with season or region

26 INTERANNUAL VARIABILITY SUMMARY + Interannual variability in PPT, T min, and T max 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

27 SUMMARY FUTURE PATTERNS? + Extraregional forcing from altered atmospheric composition, land cover change + Strong, complex regional and elevation dependent reworking of this forcing by mountain climatic processes atmospheric, hydrological, and ecological Amplification or reduction of lowland signal, or decoupling

28 Further reading: Kittel, T.G.F., P.E. Thornton, J.A. Royle, and T.N. Chase Climates of the Rocky Mountains: Historical and Future Patterns. Pages (Chapter 4), in: J.S. Baron (ed.). Rocky Mountain Futures: An Ecological Perspective. Island Press, Covelo, CA.