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Observations of Cooling Summer Daytime Observations of Cooling Summer Daytime Temperatures (1948-2005) in Temperatures (1948-2005) in

GrowingGrowing UrbanUrban Coastal California Air Coastal California Air Basins Basins

Prof. Robert BornsteinProf. Robert Bornstein

Dept. of Meteorology, San Jose State UniversityDept. of Meteorology, San Jose State Universitypblmodel@hotmail.com

Prof. Jorge Gonzalez and Bereket LebassiProf. Jorge Gonzalez and Bereket Lebassi

Dept. of Mechanical Engineering, Santa Clara U. Dept. of Mechanical Engineering, Santa Clara U.

Presented at thePresented at theAGU Fall MeetingAGU Fall Meeting

San Francisco, CA San Francisco, CA 15-19 Dec. 200815-19 Dec. 2008

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BackgroundBackground• Global & CA observations Global & CA observations generallygenerally show show

– asymmetric warming (more warming for Tasymmetric warming (more warming for Tminmin than for Tthan for Tmaxmax) )

– acceleration since mid-1970s acceleration since mid-1970s

• CA downscaledCA downscaled global-modeling global-modeling (see (see graph)graph) – done (at SCU & elsewhere) onto 10 km grids done (at SCU & elsewhere) onto 10 km grids – shows summer warming that decreases shows summer warming that decreases

towards the coast towards the coast (but does not show (but does not show coastal cooling)coastal cooling)

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Statistically down-scaled (Prof. Maurer, Statistically down-scaled (Prof. Maurer, SCUSCU) 1950-2000 ) 1950-2000 annual annual summer (JJA)summer (JJA) temp-changes ( temp-changes (00C) show warming C) show warming rates that decrease towards coast, where rates that decrease towards coast, where red dotsred dots are are

COOP sites used in present study & COOP sites used in present study & boxesboxes are study sub- are study sub-areasareas

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Previous CA Climate-change studies Previous CA Climate-change studies (next 2 slides)(next 2 slides) have explained their have explained their

obsobsin terms of increased:in terms of increased:

• Coastal upwellingCoastal upwelling ( (Bakum ‘90)Bakum ‘90)

• SSTs & urbanizationSSTs & urbanization (Goodridge ‘91) (Goodridge ‘91)

• Cloud coverCloud cover ( (Nemani et al. ’01)Nemani et al. ’01)

• IrrigationIrrigation (Christy et al. ’06, Bonfils & (Christy et al. ’06, Bonfils & Duffy ’07, Lobell & Bonfils et al. ‘08)Duffy ’07, Lobell & Bonfils et al. ‘08)

55

Publication Parameter Studied Finding

Goodridge (1991)

80 years of annual-average daily Tave

at 112 site

Warming in both coastal (attributed to warming SSTs) & inland urban (attributed to UHI effects) areas; cooling in inland rural areas was unexplained

Nemani et al. (2001)

Sites in Napa & Son-oma Valleys during 1951-97 for Tmin & Tmax

Tmin increased & Tmax slightly

decreased, both attributed to measured increased cloud cover. Increased annual coastal TD

related to increased SSTs

Duffy et al. (2006)

Interpolated (to grid) monthly-average Tave from 1950-99

Warming in all seasons, attributed to increased UHIs or GHGs

Christy et al. (2006)

18 Central Valley sites from 1910-2003 for Tave Tmax,

& Tmin

Increased Tave & Tmin in all seasons,

greater in summer & fall. Summer cooling Tmax & warming

TD values attributed to increased

summer irrigation

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Bonfils & Duffy (2007)

Christy et al. (2006) Tmin

Warming Tmin not due to irri-

gation, which could only overcome GHG-warming for Tmax

Bonfils & Lobell (2007) and Lobell & Bonfils (2008)

Gridded Tmax &

Tmin

Expanded irrigation cooled sum-mer Tmax, while producing negli-

gible effects on Tmin

LaDochy et al. (2007)

331 sites during 1950-2000 for Tave, Tmin, & Tmax

Annual Tave warming at most sites.

Almost all increases due to changes in Tmin (max in sum-mer), as Tmax

showed no change or cooling. Max Tave warming in southern CA, but

NE Interior Basin showed cooling

Abatzoglou et al. (2008)

Coastal sites during 1970-2000 for Tmax

Significant coastal cooling in late summer & early fall

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Current HypothesisCurrent HypothesisINCREASEDINCREASED GHG-INDUCED GHG-INDUCED INLAND TEMPSINLAND TEMPSINCREASED (COAST TO INCREASED (COAST TO INLAND) PRESSURE & TEMP INLAND) PRESSURE & TEMP GRADIENTSGRADIENTS INCREASED INCREASED SEA BREEZESEA BREEZE FREQ, FREQ, INTENSITY, PENETRATION, INTENSITY, PENETRATION, &/OR DURATION &/OR DURATION COASTAL AREAS SHOULD COASTAL AREAS SHOULD SHOW SHOW COOLING SUMMER COOLING SUMMER DAYTIME MAX TEMPSDAYTIME MAX TEMPS (i.e., A (i.e., A REVERSE REACTION)REVERSE REACTION)NOTES:NOTES: NOT TOTALLY NEW IDEANOT TOTALLY NEW IDEANEW WORK TO APPEAR NEW WORK TO APPEAR IN J. IN J. OF CLIMATE OF CLIMATE

88

CURRENT DATACURRENT DATA

• NCDC DAILY MAX & MIN 2-METER NCDC DAILY MAX & MIN 2-METER TEMPSTEMPS – FROM ABOUT 300 CA NWS COOP SITES FROM ABOUT 300 CA NWS COOP SITES – FOR 1948-2005FOR 1948-2005– USED IN MANY OTHER CA CLIMATE-USED IN MANY OTHER CA CLIMATE-

CHANGE STUDIESCHANGE STUDIES

• ERA40 1.4 DEG T-85 REANALYSIS JJA ERA40 1.4 DEG T-85 REANALYSIS JJA 1000-LST 1000-LST – SEA-LEVEL PRESSURE TRENDS SEA-LEVEL PRESSURE TRENDS – FOR 1970-2005FOR 1970-2005

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Results 1:Results 1: SoCAB 1970-2005 summer (JJA) T SoCAB 1970-2005 summer (JJA) Tmax max warming/ warming/ cooling trends (cooling trends (00C/decade); C/decade); solid, crossed, & open solid, crossed, & open

circles show stat p-values < 0.01, 0.05, & not circles show stat p-values < 0.01, 0.05, & not

significant, respectivelysignificant, respectively

??

????

1010

Results 2:Results 2: SFBA & CV 1970-2005 JJA SFBA & CV 1970-2005 JJA T Tmaxmax warming/cooling trends ( warming/cooling trends (00C/decade), as in previous C/decade), as in previous

figurefigure

??

??

??

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• LOWER TRENDSLOWER TRENDS FROM 1950- 70 FROM 1950- 70 (EXCEPT FOR T(EXCEPT FOR TMAX)

• Curve b:Curve b: T TMIN HAD HAD FASTEST RISE (AS FASTEST RISE (AS EXPECTED)EXPECTED)

• Curve c:Curve c: T TMAX HAD SLOWEST RISE; IT IS A SMALL-∆ B/T BIG POS VALUE & BIG NEG-VALUE (AS IN ABOVE 2 GRAPHS)

• CURVE a:CURVE a: TAVE THUS THUS ROSE AT MID RATE ROSE AT MID RATE

• Curve d:Curve d: DTR THUS DTR THUS

DECREASED (AS DECREASED (AS TTMAX FALLS & FALLS & TTMIN RISES)RISES)

Results 3: JJA Temp trends; all CA-sites

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Significance of These all-CA Significance of These all-CA TrendsTrends

• HIGHER TRENDS FROM 1970-2005 HIGHER TRENDS FROM 1970-2005 FOCUS NEEDED ON THIS PERIOD

• TTMIN HAS FASTER RISE HAS FASTER RISE

ASSYMETRIC WARMING IN LITERATUREASSYMETRIC WARMING IN LITERATURE

• TTMAX HAS SLOWER RISE, BECAUSE IT IS A SMALL DIFFERENCE B/T BIG POS-VALUE & BIG NEG-VALUE (AS SEEN IN SPATIAL PLOTS)

• TAVE & DTR ARE ALSO THUS DTR ARE ALSO THUS “CONTAMINATED” “CONTAMINATED”

• NEXT 2 SLIDES THUS SHOW NEXT 2 SLIDES THUS SHOW SEPARATE SEPARATE ANALYSESANALYSES OF CA COASTAL AND INLAND AREAS OF CA COASTAL AND INLAND AREAS

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Result 4: JJA TResult 4: JJA Tave, T, Tmin, T, Tmax, & DTR TRENDS FOR, & DTR TRENDS FOR

INLAND-WARMING INLAND-WARMING SITES OF SoCAB & SFBASITES OF SoCAB & SFBA

Curve b:Curve b: T TMIN

INCREASED (EXPECTED)(EXPECTED)

Curve c:Curve c: T TMAX HAD FASTER RISE; (UNEXPECTED), (UNEXPECTED), COULD BE DUE TO COULD BE DUE TO INCREASED UHIsINCREASED UHIs

CURVE a:CURVE a: TAVE THUS THUS

ROSE AT MID RATEROSE AT MID RATE

Curve d:Curve d: DTR THUS DTR THUS INCREASED (AS TINCREASED (AS TMAX ROSE FASTER THAN FASTER THAN TTMIN ROSE ROSE

bb

cc

aa

dd

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Result 5: JJA TResult 5: JJA Tave, T, Tmin, T, Tmax, & DTR TRENDS FOR , & DTR TRENDS FOR

COASTAL-COOLINGCOASTAL-COOLING SITES OF SoCAB & SFBA SITES OF SoCAB & SFBA

Curve b:Curve b: T TMIN ROSE ROSE

(EXPECTED)(EXPECTED)

Curve c:Curve c: T TMAX HAD COOL-ING (UNEXPECTED (UNEXPECTED MAJOR MAJOR RESULTRESULT OF STUDY) OF STUDY)

CURVE a:CURVE a: TAVE THUS SHOWED ALMOST NO CHANGE, AS FOUND IN LIT.), AS RISING T AS RISING Tmin & &

FALLING TFALLING Tmax CHANGES ALMOST CANCELLED OUT

Curve d:Curve d: DTR THUS DE- DTR THUS DE-CREASED, AS TCREASED, AS TMIN ROSE &

TTMAX FELL FELL

aa

bb

cc

dd

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Note IPCC 2001 cooling over SFBA!!

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Significance of These Coastal-Significance of These Coastal-Cooling and Inland-Warming Cooling and Inland-Warming

TrendsTrends

• CA ASSYMETRIC WARMINGCA ASSYMETRIC WARMING IN LITERATURE IS IN LITERATURE IS HEREIN SHOWN TO BE DUE TO CONCURRENT HEREIN SHOWN TO BE DUE TO CONCURRENT COOLING TTMAX IN COASTAL AREAS & WARMING TTMAX IN INLAND AREAS

• PREVIOUS CA STUDIESPREVIOUS CA STUDIES – THAT DID NOT LOOK SPECIFICALLY AT THAT DID NOT LOOK SPECIFICALLY AT SUMMER SUMMER

DAYTIME COASTAL VS. INLAND VALUESDAYTIME COASTAL VS. INLAND VALUES HAVE HAVE THUS REPORTED THUS REPORTED CONTAMINATEDCONTAMINATED T TMAX, T, TAVE, & DTR , & DTR VALUESVALUES

– HOWEVER, ARE HOWEVER, ARE NOT INCONSISTENTNOT INCONSISTENT WITH WITH CURRENT RESULTS, THEY ARE JUST NOT AS CURRENT RESULTS, THEY ARE JUST NOT AS DETAILED IN THEIR ANALYSES AND THEIR RESULTSDETAILED IN THEIR ANALYSES AND THEIR RESULTS

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Trend in 1979-2002 ERA40 reanalysis of Trend in 1979-2002 ERA40 reanalysis of 1800 UTC (1000 LT) JJA 1800 UTC (1000 LT) JJA sea-level p-changessea-level p-changes

(hPa/decade)(hPa/decade)• dotsdots =1.4-deg =1.4-deg gridsgrids• end-ptsend-pts of of solid lines = pts solid lines = pts for for p-grad p-grad trend trend calcu-lation calcu-lation (next slide)(next slide)

• H & L:H & L: strength-ened strength-ened & moved to NW & moved to NW (can’t see in (can’t see in this slide)this slide)

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Result 6:Result 6: Trends in sea minus land JJA 1800 Trends in sea minus land JJA 1800 UTC UTC

sea-level sea-level p- gradientp- gradient (hPa/100-km/decade) (hPa/100-km/decade)

from values at ends of lines in prev. Fig.from values at ends of lines in prev. Fig. Key:Key:

SFBA (red) SFBA (red) SoCAB SoCAB (blue)(blue)

These stronger These stronger HPGFsHPGFs stronger stronger sea breezessea breezes coastal coastal coolingcooling

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Result 7. JJA 1970-2005 2 m max-T trends for 4 Result 7. JJA 1970-2005 2 m max-T trends for 4 pairs of pairs of urban (red, solid) & rural (blue, dashed)urban (red, solid) & rural (blue, dashed)

sitessitesNotes:Notes:1.1. All sites are near the All sites are near the

cooling-warming cooling-warming borderborder

2.2. UHI-TRENDUHI-TREND = = absolute sumabsolute sum b/t b/t warming-urban & warming-urban & cooling-rural trends cooling-rural trends (K/decade)(K/decade)

3. 3. SFBASFBA sites sites(a)(a) Stockton (0.55)Stockton (0.55)(b)(b) Sac. (0.51)Sac. (0.51)

4. 4. SoCABSoCAB sites sites(c) Pasadena (0.26)(c) Pasadena (0.26)(d) S. Ana (0.12)(d) S. Ana (0.12)

2020

Notes on JJA daytime Notes on JJA daytime UHI-trendUHI-trend results results

• The The fastest growingfastest growing cities had the fastest cities had the fastest growing UHIsgrowing UHIs

• As As no coastal sitesno coastal sites showed warming T-max showed warming T-max values, the calculation could only be done values, the calculation could only be done at these four pairs, located at the inland at these four pairs, located at the inland boundary b/t the warming and cooling boundary b/t the warming and cooling areasareas

• The coastal sites would have The coastal sites would have cooled even cooled even moremore w/o their (assumed) growing UHIs w/o their (assumed) growing UHIs

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BENEFICIAL IMPLICATIONS OF BENEFICIAL IMPLICATIONS OF COASTAL COOLINGCOASTAL COOLING

• NAPA WINE NAPA WINE AREAS MAY NOT GO EXTINCTAREAS MAY NOT GO EXTINCT (REALLY GOOD NEWS!); (REALLY GOOD NEWS!); SEE SEE MAPMAP

• LOWER HUMAN LOWER HUMAN HEAT-STRESSHEAT-STRESS RATES RATES

• OZONE CONCENTRATIONSOZONE CONCENTRATIONS MIGHT CONTINUE MIGHT CONTINUE TO DECREASE, AS LOWER MAX-TEMPS TO DECREASE, AS LOWER MAX-TEMPS REDUCEREDUCE– ANTHROPOGENIC EMISSIONSANTHROPOGENIC EMISSIONS– BIOGENIC EMISSIONSBIOGENIC EMISSIONS– PHOTOLYSIS RATESPHOTOLYSIS RATES

• ENERGYENERGY FOR COOLING MAY NOT INCREASE FOR COOLING MAY NOT INCREASE AS RAPIDLY AS POPULATION AS RAPIDLY AS POPULATION (NEXT GRAPH)(NEXT GRAPH)

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NAPA WINE AREAS MAY NAPA WINE AREAS MAY NOT GO EXTINCTNOT GO EXTINCT DUE TO DUE TO ALLEGED RISING TALLEGED RISING TMAX VALUES, AS PREDICTED IN NAS VALUES, AS PREDICTED IN NAS

STUDYSTUDY

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Result 6: Peak-Summer Result 6: Peak-Summer Per-capita Per-capita Electricity-Electricity-TrendsTrends

Down-trend at Down-trend at cooling cooling Coastal: LA (blue) & Pasadena Coastal: LA (blue) & Pasadena ((pinkpink, 8.5%/decade), 8.5%/decade) > Up-trend at warming > Up-trend at warming inland Riversideinland Riverside (green)(green)

Up-trend at Up-trend at warming warming Sac & Santa ClaraSac & Santa Clara

Need:Need: detailed detailed energy-useenergy-use data for more sitesdata for more sites to consider changed to consider changed energy energy efficiency efficiency

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POSSIBLE FUTURE EFFORTSPOSSIBLE FUTURE EFFORTS (PART 1 (PART 1 OF 2)OF 2)

• EXPAND EXPAND (TO ALL OF CA)(TO ALL OF CA)– ANALYSIS OFANALYSIS OF OBS (IN-SITU & OBS (IN-SITU & GISGIS) ) – URBANIZED MESO-MET (MM5, RAMS, WRF) URBANIZED MESO-MET (MM5, RAMS, WRF)

MODELING MODELING

• SEPARATE INFLUENCES SEPARATE INFLUENCES OF CHANGING:OF CHANGING:– LAND-USE PATTERNS RELAND-USE PATTERNS RE

• AGRICULTURAL IRRIGATIONAGRICULTURAL IRRIGATION• URBANIZATION & UHI-MAGNITUDEURBANIZATION & UHI-MAGNITUDE

– SEA BREEZE:SEA BREEZE:INTENSITY, FREQ, DURATION, &/OR PENETRATION INTENSITY, FREQ, DURATION, &/OR PENETRATION

• DETERMINE POSSIBLE DETERMINE POSSIBLE “SATURATION”“SATURATION” OF OF SEA- BREEZE EFFECTS FROMSEA- BREEZE EFFECTS FROM

• FLOW-VELOCITY & COLD-AIR TRANSPORTFLOW-VELOCITY & COLD-AIR TRANSPORT• AND/OR STRATUS-CLOUD EFFECTS ON LONG- & SHORT-AND/OR STRATUS-CLOUD EFFECTS ON LONG- & SHORT-

WAVE RADIATIONWAVE RADIATION

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POSSIBLE FUTURE EFFORTS POSSIBLE FUTURE EFFORTS (PART 2 (PART 2 OF 2)OF 2)

• DETERMINE CUMULATIVE FREQ DISTRIBU-DETERMINE CUMULATIVE FREQ DISTRIBU-TIONSTIONS OF MAX-TEMP VALUES, AS OF MAX-TEMP VALUES, AS– EVEN IF EVEN IF AVERAGEAVERAGE MAX-VALUES DECREASE, MAX-VALUES DECREASE,– EXTREMEEXTREME MAX-VALUES MAY STILL INCREASE (IN MAX-VALUES MAY STILL INCREASE (IN

INTENSITY AND/OR FREQUENCY)INTENSITY AND/OR FREQUENCY)

• DETERMINE CHANGES IN LARGE-SCALE DETERMINE CHANGES IN LARGE-SCALE ATMOSPHERIC FLOWS:ATMOSPHERIC FLOWS:– HOW DOES GLOBAL CLIMATE-CHANGE EFFECT HOW DOES GLOBAL CLIMATE-CHANGE EFFECT

POSIT-ION & STRENGTH OF: POSIT-ION & STRENGTH OF: PACIFIC HIGH & PACIFIC HIGH & THERMAL LOW?THERMAL LOW?

– THIS IS THIS IS ULTIMATE CAUSEULTIMATE CAUSE OF CLIMATE-CHANGE OF CLIMATE-CHANGE

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Thanks for listening!Thanks for listening!

Questions?Questions?