CHARACTERIZING REGIONAL MODES OF CLIMATE
VARIABILITY IN CALIFORNIA
JOHN T. ABATZOGLOU, KELLY T. REDMOND,
AND LAURA M. EDWARDS
Western Regional Climate Center, Desert Research Institute, Reno NV
PACLIM 2007
Talk Outline
• Motivation for redefining climate regions
• Climate regionalization procedure
• Mechanisms for regional climate variability
Motivation
•
•
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Evaluate current NCDC Climate Divisions
Improve understanding of mechanisms
for regional scale climate processes
Improve monitoring of climate variability
and trends
Goals
• Develop an objective means to monitor regional scale climate
variability for the state of California
• Aggregate available datasets extending as far back in time and
provide monthly updates
• Provide a suite of user-friendly tools and graphics for public
consumption
California: A Suitable Testbed
Regional Scale Variability
1.
2.
3.
4.
Latitude
Coastal Influence
Sharp Topographic Gradients
Mixed extratropical &
monsoonal modes
Elements of Interest
Temperature
Precipitation
Currently: Monthly Timescales
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•
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Data Sources: COOP stations, PRISM-gridded data
Monthly mean maximum and minimum temperatures and
accumulated monthly precipitation
1949-2005
Abrupt Climate Change?
Monthly Mean Maximum Temperature
Yosemite Park Headquarters
Algorithm used to assess
and correct for climate
inhomogeneities w/o use
of metadata
Climate Regionalization I
Fundamental Questions
•
What stations/parts of the state covary with one
another?
•
How many distinct climate regions are located within
the state?
•
What physical/dynamical mechanisms are
responsible for the observed patterns?
You are here
JJA TMAX Correlation to Pacific Grove, CA
DJF TMAX Correlation to Pacific Grove, CA
Water Year PRCP Correlation to Pacific Grove, CA
Climate Regionalization II
Implementation
•
Elements converted to standard anomalies* and
correlation matrix used
•
PCA (Temperature & Precipitation)
•
Oblique rotation yields most stable results for
regionalization process
REOFS 5 & 6 from PRISM
REOFS 1 & 3 from COOP
Climate Divisions v. Climate Regions
A. Non-statistical methods used
in creation
A. Objectively defined
B. Insensitive to Topography
B. Topographic and coastal
environs well defined
C. Only Mean Temperature and
Precipitation
C. Also includes Maximum and
Minimum Temperature data
Mechanisms of Regional Climate
Variability
• Two examples
– Sierra vs. Valley
– South Coastal vs. Southern Interior
Warm Sierra/Cool Valley
Cool Sierra/Warm Valley
Decoupling of Sierra and Central Valley
Composite 500hPa Geopotential Height Anomalies
Cool Valley / Warm Sierra
Pronounced ridge over
western N. America
- PRCP Anomaly
Cool Sierra / Warm Valley
Zonal flow into N/C
California
+PRCP Anomaly
Warm Interior/Cool Coast
Cool Interior/Warm Coast
Decoupling of South Coast & South Interior
Correlation of Aug-Oct SST
w/ Interior-Coast Maximum
Temperature Gradient
Coast-Inland Temperature Gradient
•
Strong signature of immediate coastal SST (r=0.6) w/ PDO flavor (r=0.41)
•
Concomitant SOI/Nino3 (ASO), r=0.31 / 0.32
Cool Interior/
Warm Coast
Cool Interior/
Warm Coast
Possible monsoonal signal tied to TMAX gradient
Mechanisms to link near Coastal SST to
regional scale variability…
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Monthly updates of regional datasets from Jan 1895-present
Spatial/temporal information on precip/temp across the state
Simple trend analysis and statistical significance
User friendly graphics
– Nevada Climate tracker included as well
http://www.wrcc.dri.edu/monitor/cal-mon/
Asymmetric Climate Trends I
Asymmetric Climate Trends II
1975-2006
1950-2006
1975-2006
1950-2006
Lower-Atmosphere Trends from
NCEP/NCAR Reanalysis
Trends from California Reanalysis Downscaling at 10-km (CaRD10)
Summary
•
Novel regionalization technique appears useful in objectively
identifying climate regions within California
•
Regionalization illuminates regional-scale climate barriers that
may be useful for the research community in elucidating
mechanisms for regional climate variability/change and
predictability
•
California Climate Tracker: a friendly graphical interface for
public needs, superior to NCDC divisional datasets
http://www.wrcc.dri.edu/monitor/cal-mon/
Accumulated Differential ( TREF − TCAN)
0
−10
−20
−30
−40
−50
−60
−70
−80
−90
1950
55
60
65
70
75
80
85
90
95
2000
05