1. 1 Observations of Cooling Summer Daytime Temperatures (1948-2005) in Growing Urban Coastal California Air Basins Prof. Robert Bornstein Dept. of Meteorology, San Jose State University pblmodel@hotmail.com Prof. Jorge Gonzalez and Bereket Lebassi Dept. of Mechanical Engineering, Santa Clara U. Presented at the AGU Fall Meeting San Francisco, CA 15-19 Dec. 2008

2. 2 Background Global & CA observations generally show Global & CA observations generally show –asymmetric warming (more warming for T min than for T max ) –acceleration since mid-1970s CA downscaled global-modeling (see graph) CA downscaled global-modeling (see graph) –done (at SCU & elsewhere) onto 10 km grids –shows summer warming that decreases towards the coast (but does not show coastal cooling)

3. 3 Statistically down-scaled (Prof. Maurer, SCU) 1950-2000 annual summer (JJA) temp-changes ( 0 C) show warming rates that decrease towards coast, where red dots are COOP sites used in present study & boxes are study sub-areas

4. 4 Previous CA Climate-change studies (next 2 slides) have explained their obs in terms of increased: Coastal upwelling (Bakum ‘90) Coastal upwelling (Bakum ‘90) SSTs & urbanization (Goodridge ‘91) SSTs & urbanization (Goodridge ‘91) Cloud cover (Nemani et al. ’01) Cloud cover (Nemani et al. ’01) Irrigation (Christy et al. ’06, Bonfils & Duffy ’07, Lobell & Bonfils et al. ‘08) Irrigation (Christy et al. ’06, Bonfils & Duffy ’07, Lobell & Bonfils et al. ‘08)

5. 5 PublicationParameter StudiedFinding Goodridge (1991) 80 years of annual- average daily T ave 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 T min & T max T min increased & T max slightly decreased, both attributed to measured increased cloud cover. Increased annual coastal T D related to increased SSTs Duffy et al. (2006) Interpolated (to grid) monthly-average T ave 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 T ave T max, & T min Increased T ave & T min in all seasons, greater in summer & fall. Summer cooling T max & warming T D values attributed to increased summer irrigation

6. 6 Bonfils & Duffy (2007) Christy et al. (2006) T min Warming T min not due to irri- gation, which could only overcome GHG-warming for T max Bonfils & Lobell (2007) and Lobell & Bonfils (2008) Gridded T max & T min Expanded irrigation cooled sum- mer T max, while producing negli- gible effects on T min LaDochy et al. (2007) 331 sites during 1950-2000 for T ave, T min, & T max Annual T ave warming at most sites. Almost all increases due to changes in T min (max in sum-mer), as T max showed no change or cooling. Max T ave warming in southern CA, but NE Interior Basin showed cooling Abatzoglou et al. (2008) Coastal sites during 1970- 2000 for T max Significant coastal cooling in late summer & early fall

7. 7 Current Hypothesis INCREASED GHG-INDUCED INLAND TEMPS  INCREASED (COAST TO INLAND) PRESSURE & TEMP GRADIENTS  INCREASED SEA BREEZE FREQ, INTENSITY, PENETRATION, &/OR DURATION  COASTAL AREAS SHOULD SHOW COOLING SUMMER DAYTIME MAX TEMPS (i.e., A REVERSE REACTION) NOTES:  NOT TOTALLY NEW IDEA  NEW WORK TO APPEAR IN J. OF CLIMATE

8. 8 CURRENT DATA NCDC DAILY MAX & MIN 2-METER TEMPS NCDC DAILY MAX & MIN 2-METER TEMPS –FROM ABOUT 300 CA NWS COOP SITES –FOR 1948-2005 –USED IN MANY OTHER CA CLIMATE-CHANGE STUDIES ERA40 1.4 DEG T-85 REANALYSIS JJA 1000- LST ERA40 1.4 DEG T-85 REANALYSIS JJA 1000- LST –SEA-LEVEL PRESSURE TRENDS –FOR 1970-2005

9. 9 Results 1: SoCAB 1970-2005 summer (JJA) T max warming/ cooling trends ( 0 C/decade); solid, crossed, & open circles show stat p-values < 0.01, 0.05, & not significant, respectively ? ? ?

10. 10 Results 2: SFBA & CV 1970-2005 JJA T max warming/cooling trends ( 0 C/decade), as in previous figure ? ? ?

11. 11 LOWER TRENDS FROM 1950- 70 (EXCEPT FOR TLOWER TRENDS FROM 1950- 70 (EXCEPT FOR T MAX ) Curve b: THAD FASTEST RISE (AS EXPECTED)Curve b: T MIN HAD FASTEST RISE (AS EXPECTED) Curve c: TCurve c: T MAX HAD SLOWEST RISE; IT IS A SMALL-∆ B/T BIG POS VALUE & BIG NEG-VALUE (AS IN ABOVE 2 GRAPHS) CURVE a: THUS ROSE AT MID RATECURVE a: T AVE THUS ROSE AT MID RATE Curve d: DTR THUSCurve d: DTR THUS DECREASED (AS T FALLS & T RISES) DECREASED (AS T MAX FALLS & T MIN RISES) Results 3: JJA Temp trends; all CA-sites

12. 12 Significance of These all-CA Trends HIGHER TRENDS FROM 1970-2005 HIGHER TRENDS FROM 1970-2005  FOCUS NEEDED ON THIS PERIOD THAS FASTER RISE  T MIN HAS FASTER RISE  ASSYMETRIC WARMING IN LITERATURE T T MAX HAS SLOWER RISE, BECAUSE IT IS A SMALL DIFFERENCE B/T BIG POS-VALUE & BIG NEG-VALUE (AS SEEN IN SPATIAL PLOTS) DTR ARE ALSO THUS “CONTAMINATED” T AVE & DTR ARE ALSO THUS “CONTAMINATED” NEXT 2 SLIDES THUS SHOW SEPARATE ANALYSES OF CA COASTAL AND INLAND AREAS NEXT 2 SLIDES THUS SHOW SEPARATE ANALYSES OF CA COASTAL AND INLAND AREAS

13. 13 Result 4: JJA T, T, T, & DTR TRENDS FOR Result 4: JJA T ave, T min, T max, & DTR TRENDS FOR INLAND-WARMING SITES OF SoCAB & SFBA Curve b: T (EXPECTED) Curve b: T MIN INCREASED (EXPECTED) Curve c: T (UNEXPECTED), COULD BE DUE TO INCREASED UHIs Curve c: T MAX HAD FASTER RISE; (UNEXPECTED), COULD BE DUE TO INCREASED UHIs CURVE a: THUS ROSE AT MID RATE CURVE a: T AVE THUS ROSE AT MID RATE Curve d: DTR THUS INCREASED (AS T FASTER THAN T ROSE Curve d: DTR THUS INCREASED (AS T MAX ROSE FASTER THAN T MIN ROSE b c a d

14. 14 Result 5: JJA T, T, T, & DTR TRENDS FOR Result 5: JJA T ave, T min, T max, & DTR TRENDS FOR COASTAL-COOLING SITES OF SoCAB & SFBA Curve b: TROSE (EXPECTED) Curve b: T MIN ROSE (EXPECTED) Curve c: T (UNEXPECTED MAJOR RESULT OF STUDY) Curve c: T MAX HAD COOL- ING (UNEXPECTED MAJOR RESULT OF STUDY) CURVE a: AS RISING T & FALLING T CURVE a: T AVE THUS SHOWED ALMOST NO CHANGE, AS FOUND IN LIT.), AS RISING T min & FALLING T max CHANGES ALMOST CANCELLED OUT Curve d: DTR THUS DE- CREASED, AS T T FELL Curve d: DTR THUS DE- CREASED, AS T MIN ROSE & T MAX FELL a b c d

15. 15 Note IPCC 2001 cooling over SFBA!!

16. 16 Significance of These Coastal-Cooling and Inland-Warming Trends CA ASSYMETRIC WARMING IN LITERATURE IS HEREIN SHOWN TO BE DUE TO CONCURRENT T T CA ASSYMETRIC WARMING IN LITERATURE IS HEREIN SHOWN TO BE DUE TO CONCURRENT COOLING T MAX IN COASTAL AREAS & WARMING T MAX IN INLAND AREAS PREVIOUS CA STUDIES PREVIOUS CA STUDIES –THAT DID NOT LOOK SPECIFICALLY AT SUMMER DAYTIME COASTAL VS. INLAND VALUES HAVE THUS REPORTED CONTAMINATED T, T, & DTR VALUES –THAT DID NOT LOOK SPECIFICALLY AT SUMMER DAYTIME COASTAL VS. INLAND VALUES HAVE THUS REPORTED CONTAMINATED T MAX, T AVE, & DTR VALUES –HOWEVER, ARE NOT INCONSISTENT WITH CURRENT RESULTS, THEY ARE JUST NOT AS DETAILED IN THEIR ANALYSES AND THEIR RESULTS

17. 17 Trend in 1979-2002 ERA40 reanalysis of 1800 UTC (1000 LT) JJA sea-level p-changes (hPa/decade) dots =1.4-deg grids dots =1.4-deg grids end-pts of solid lines = pts for p- grad trend calcu- lation (next slide) end-pts of solid lines = pts for p- grad trend calcu- lation (next slide) H & L: strength- ened & moved to NW (can’t see in this slide) H & L: strength- ened & moved to NW (can’t see in this slide)

18. 18 Result 6: Trends in sea minus land JJA 1800 UTC sea-level p- gradient (hPa/100-km/decade) from values at ends of lines in prev. Fig. Key: SFBA (red) SoCAB (blue) These stronger HPGFs  stronger sea breezes  coastal cooling

19. 19 Result 7. JJA 1970-2005 2 m max-T trends for 4 pairs of urban (red, solid) & rural (blue, dashed) sites Notes: 1.All sites are near the cooling-warming border 2.UHI-TREND = absolute sum b/t warming-urban & cooling-rural trends (K/decade) 3. SFBA sites (a) Stockton (0.55) (b) Sac. (0.51) 4. SoCAB sites (c) Pasadena (0.26) (d) S. Ana (0.12)

20. 20 Notes on JJA daytime UHI-trend results The fastest growing cities had the fastest growing UHIs The fastest growing cities had the fastest growing UHIs As no coastal sites showed warming T-max values, the calculation could only be done at these four pairs, located at the inland boundary b/t the warming and cooling areas As no coastal sites showed warming T-max values, the calculation could only be done at these four pairs, located at the inland boundary b/t the warming and cooling areas The coastal sites would have cooled even more w/o their (assumed) growing UHIs The coastal sites would have cooled even more w/o their (assumed) growing UHIs

21. 21 BENEFICIAL IMPLICATIONS OF COASTAL COOLING NAPA WINE AREAS MAY NOT GO EXTINCT (REALLY GOOD NEWS!); SEE MAP NAPA WINE AREAS MAY NOT GO EXTINCT (REALLY GOOD NEWS!); SEE MAP LOWER HUMAN HEAT-STRESS RATES LOWER HUMAN HEAT-STRESS RATES OZONE CONCENTRATIONS MIGHT CONTINUE TO DECREASE, AS LOWER MAX-TEMPS REDUCE OZONE CONCENTRATIONS MIGHT CONTINUE TO DECREASE, AS LOWER MAX-TEMPS REDUCE –ANTHROPOGENIC EMISSIONS –BIOGENIC EMISSIONS –PHOTOLYSIS RATES ENERGY FOR COOLING MAY NOT INCREASE AS RAPIDLY AS POPULATION (NEXT GRAPH) ENERGY FOR COOLING MAY NOT INCREASE AS RAPIDLY AS POPULATION (NEXT GRAPH)

22. 22 NAPA WINE AREAS MAY NOT GO EXTINCT DUE TO ALLEGED RISING T VALUES, AS PREDICTED IN NAS STUDY NAPA WINE AREAS MAY NOT GO EXTINCT DUE TO ALLEGED RISING T MAX VALUES, AS PREDICTED IN NAS STUDY

23. 23 Result 6: Peak-Summer Per-capita Electricity-Trends  Down-trend at cooling Coastal: LA (blue) & Pasadena (pink, 8.5%/decade) > Up-trend at warming inland Riverside (green) Up-trend at warming Sac & Santa Clara Need:  detailed energy-use data for more sites  to consider changed energy efficiency

24. 24 POSSIBLE FUTURE EFFORTS (PART 1 OF 2) EXPAND (TO ALL OF CA) EXPAND (TO ALL OF CA) –ANALYSIS OF OBS (IN-SITU & GIS) –URBANIZED MESO-MET (MM5, RAMS, WRF) MODELING SEPARATE INFLUENCES OF CHANGING: SEPARATE INFLUENCES OF CHANGING: – LAND-USE PATTERNS RE AGRICULTURAL IRRIGATION AGRICULTURAL IRRIGATION URBANIZATION & UHI-MAGNITUDE URBANIZATION & UHI-MAGNITUDE –SEA BREEZE: INTENSITY, FREQ, DURATION, &/OR PENETRATION DETERMINE POSSIBLE “SATURATION” OF SEA- BREEZE EFFECTS FROM DETERMINE POSSIBLE “SATURATION” OF SEA- BREEZE EFFECTS FROM FLOW-VELOCITY & COLD-AIR TRANSPORT FLOW-VELOCITY & COLD-AIR TRANSPORT AND/OR STRATUS-CLOUD EFFECTS ON LONG- & SHORT-WAVE RADIATION AND/OR STRATUS-CLOUD EFFECTS ON LONG- & SHORT-WAVE RADIATION

25. 25 POSSIBLE FUTURE EFFORTS (PART 2 OF 2) DETERMINE CUMULATIVE FREQ DISTRIBU- TIONS OF MAX-TEMP VALUES, AS DETERMINE CUMULATIVE FREQ DISTRIBU- TIONS OF MAX-TEMP VALUES, AS –EVEN IF AVERAGE MAX-VALUES DECREASE, –EXTREME MAX-VALUES MAY STILL INCREASE (IN INTENSITY AND/OR FREQUENCY) DETERMINE CHANGES IN LARGE-SCALE ATMOSPHERIC FLOWS: DETERMINE CHANGES IN LARGE-SCALE ATMOSPHERIC FLOWS: –HOW DOES GLOBAL CLIMATE-CHANGE EFFECT POSIT- ION & STRENGTH OF: PACIFIC HIGH & THERMAL LOW? –THIS IS ULTIMATE CAUSE OF CLIMATE-CHANGE

26. 26 Thanks for listening! Questions?