ANALYSIS OF CALIFORNIA SURFACE TEMPERATURE TRENDS

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• ANALYSIS OF CALIFORNIA SURFACE TEMPERATURE TRENDS
  
• BASED ON OBSERVATIONS
• THESIS DEFENSE
• Wittaya Kessomkiat
• Department of Meteorology
• San José State University

Advised by Dr. Eugene Cordero Department of
Meteorology San José State University and
collaboration with Dr. Steven Mauget USDA/Agricult
ural Research Service, Plant Stress and Water
Conservation Laboratory
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Outline

• Introduction
• Data and Methodology
• Results
• Summary and Discussion
• Questions

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Introduction

• Global Scale

IPCC AR4 (2007)
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Introduction

• Global Scale
• 19502004
• Annual Tmin vs Annual Tmax
• (0.20C dec-1 vs 0.14C dec-1)
• with diurnal temperature range (DTR)
• trend at -0.07C
• 19792004
• Annual Tmin Tmax (0.29C dec-1)
• with essentially no DTR trends

Vose et al. (2005)
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Introduction Prior Work

• Prior Work California
• Christy and Norris (2006), Bonfils et al.(2006)
  Investigated land use change in the central
  valley.
• warming in minimum temperatures during summer
  nights due to irrigation
• LaDochy et al. (2007) Studied annual trends in
  CA temp since 1950.
• Tmin is stronger than TmeanTmax.
• warming trends in urban are larger than
  ruralnon-agricultural areas
• strong correlation between temperature
  variability Pacific sea surface temperatures,
  especially due to the Pacific Decadal Oscillation
  (PDO).
• Lebassi et al. (2009) Studied summertime trends
  in LA and SF basin.
• Cooling trends during JJA Tmax daytime 1970-2005
  due to sea breeze.

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Introduction Goals and Objectives

• Climate change detection in California
• Characterize change in California temperatures
  over last century
• Spatial variations
• Temporal structure
• Identify patterns of change that help determining
  the forcing mechanisms

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Data and Methodology

• Surface Data
• US Historical Climatology Network (USHCN) Urban
  Heat-Adjusted
• 54 stations in California 4 stations from
  neighboring states
• Criteria for station selection
• Length of period of record
• Percent of missing data
• Number of station moves
• other station changes that
• may affect data homogeneity,
• and spatial coverage

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Data and Methodology

• Surface Data
• Cooperative Observer Network (COOP) 272
  stations
• Good coverage
• Possible issues with data quality

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Data and Methodology

• Data Quality
• no months are used if more than 6 days are
  missing (Stafford et al. 2000).
• no annual or seasonal are used if more than one
  month is missing.
• not less than 80 of data or not less than 4
  years for each decade during selected time
  periods are used for calculating trends for time
  series (Vose et al. 2005).
• California Climate Regions defined by DRI
  (Abatzoglou et al. 2009).
• Least-Square Regression
• Linear fits accounting for auto correlation
  (Santer et al. 2000)
• 95 confidence level CL or better
• Mann-Whitney U Statistics
• Determine the most significant occurrences of
  high or low rankings years for a sampling window
  of 6-30 years (Mauget 2003)

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Results I USHCN Temperature Trends
1918-2006, 1950-2006, and 1970-2006
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Results California Trends
Tmax
Tmin
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ResultsRegional Trends
Tmin Trends (F Decade-1)
California Climate Regions (Abatzoglou et al.
2009) A North Coast Region B North Central
Region C Northeast Region D Sierra Region E
Sacramento-Delta Region F Central Coast
Region G San Joaquin Valley Region H South
Coast Region I South Interior Region J Mohave
Desert Region K Sonoran Desert Region
CA Annual and Seasonal Tmin trends (F Decade-1)
between 1918-2006
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ResultsRegional Trends
Tmax Trends (F Decade-1)
California Climate Regions (Abatzoglou et al.
2009) A North Coast Region B North Central
Region C Northeast Region D Sierra Region E
Sacramento-Delta Region F Central Coast
Region G San Joaquin Valley Region H South
Coast Region I South Interior Region J Mohave
Desert Region K Sonoran Desert Region
CA Annual and Seasonal trends (F Decade-1)
between 1918-2006
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Comparison Regional Trends during 3 Different
Time Periods
CA N-CA S-CA A B
C D E F G
H I J K
Annual Tmin
Solid color indicates significant trends at 95
CL
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Comparison Regional Trends during 3 Different
Time Periods
CA N-CA S-CA A B
C D E F G
H I J K
Annual Tmin
Solid color indicates significant trends at 95
CL
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Comparison Regional Trends during 3 Different
Time Periods
CA N-CA S-CA A B
C D E F G
H I J K
Annual Tmin
Solid color indicates significant trends at 95
CL
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Comparison Regional Trends during 3 Different
Time Periods
CA N-CA S-CA A B
C D E F G
H I J K
Annual Tmax
Solid color indicates significant trends at 95
CL
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Comparison Regional Trends during 3 Different
Time Periods
CA N-CA S-CA A B
C D E F G
H I J K
Annual Tmax
Solid color indicates significant trends at 95
CL
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Comparison Regional Trends during 3 Different
Time Periods
Seasonal Tmin
Seasonal Tmax
Solid color indicates significant trends at 95
CL
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Individual Station Trends Tmin (1950-2006)
Temperature Trends (F Decade-1) Red Warming
Trends Blue Cooling Trends
Significant 95 CL
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Individual Station Trends Tmax (1950-2006)
Temperature Trends (F Decade-1) Red Warming
Trends Blue Cooling Trends
Significant 95 CL
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Results II Mann-Whitney U Statistics for
Each Individual USHCN Station during 1918-2006
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Results
Annual Tmax
Sig. Warming Periods Dark Red - 99 CL Red -
95 CL Light Red - 90 CL
Sig. Cooling Periods Dark Blue - 99 CL Blue -
95 CL Light Blue - 90 CL
Year
Significant Warming and Cooling Periods for Each
Individual CA USHCN Stations between 1918-2006
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Results
Annual Tmax
Individual USHCN Station
California Climate Region
Sig. Warming Periods Dark Red - 99 CL Red -
95 CL Light Red - 90 CL
Sig. Cooling Periods Dark Blue - 99 CL Blue -
95 CL Light Blue - 90 CL
Year
Significant Warming and Cooling Periods for Each
Individual CA USHCN Stations between 1918-2006
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Results
Annual Tmin
Individual USHCN Station
California Climate Region
Sig. Warming Periods Dark Red - 99 CL Red -
95 CL Light Red - 90 CL
Sig. Cooling Periods Dark Blue - 99 CL Blue -
95 CL Light Blue - 90 CL
Year
Significant Warming and Cooling Periods for Each
Individual CA USHCN Stations between 1918-2006
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Results
Annual Tmax
Annual Tmin
California Climate Region
Individual USHCN Station
Year
Year
Significant Warming and Cooling Periods for Each
Individual CA USHCN Stations between 1918-2006
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Results
Seasonal Tmax
DJF
MAM
JJA
SON
California Climate Region
Individual USHCN Station
Year
Significant Warming and Cooling Periods for Each
Individual CA USHCN Stations between 1918-2006
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Results
Seasonal Tmin
DJF
MAM
JJA
SON
California Climate Region
Individual USHCN Station
Year
Significant Warming and Cooling Periods for Each
Individual CA USHCN Stations between 1918-2006
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Results IIICOOP Temperature Trendsduring
1950-2005 and 1970-2005
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COOP Annual Tmax (1950-2005)
Temperature Trends (F Decade-1) Red Warming
Trends Blue Cooling Trends
Significant 95 CL
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COOP Annual Tmin (1950-2005)
Temperature Trends (F Decade-1) Red Warming
Trends Blue Cooling Trends
Significant 95 CL
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COOP DJF Tmax (1970-2005)
Temperature Trends (F Decade-1) Red Warming
Trends Blue Cooling Trends
Significant 95 CL
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COOP JJA Tmax (1970-2005)
Temperature Trends (F Decade-1) Red Warming
Trends Blue Cooling Trends
Significant 95 CL
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Summary

• Annual Tmin trends have greater magnitude
  compared to Tmax during 1918-2006 and 1950-2006
  but show approx. same magnitude during 1970-2006
  throughout California.
• S-CA show the greater trends compared to N-CA,
  especially in Tmax during 1970-2006.
• MAM trends are found the largest trends among all
  seasons during 1950-2006 and 1970-2006 in Tmin.
• Spatial and temporal structures of warming and
  cooling for Tmax and Tmin are different.
• Tmin - coherent warming since 1978
• Tmax - warming since 1985 or later
• Cooling periods are different between Tmin and
  Tmax
• The differences between Tmax and Tmin trends
  suggest different forcing mechanisms.

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Discussion
Annual Tmin
LaDochy et al. (2007) strong correlation between
temperature variability, and Pacific sea surface
temperatures, especially due to the Pacific
Decadal Oscillation (PDO) using CA temp. since
1950.
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Discussions

• Lebassi et al. (2009) studied LA and SF basins
  and found cooling trends in JJA Tmax summertime
  during 1970-2005 caused by an enhanced sea-breeze
  circulation due to additional warming in the
  interior.
• During 1970-2005,our study found that most
  cooling stations in JJA Tmax are located along
  the Pacific coast.

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Future Work

• Climate change attribution for California
• Use these diagnostics to help model attribution
  studies
• Regional climate model
• Test influence of various processes
• Land surface variations
• SST variations
• GHG variations

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Acknowledgements

• Dr. Eugene Cordero
• Dr. Steven Mauget
• Dr. John Abatzoglou
• Mike Voss
• Prof. Robert Bornstein
• All faculty members at Dept. of Meteorology, SJSU
• All colleges, SJSU

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Questions
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Data and Methodology

• Surface Data
• USHCN Urban Heat-Adjusted 58 stations
• COOP 272 stations

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Comparison Regional Trends during 3 Different
Time Periods
CA N-CA S-CA A B C
D E F G H
I J K
Annual Tmin
CA N-CA S-CA A B C
D E F G H
I J K
Annual Tmax
Solid color indicates significant trends at 95
CL