1. 1 Cooling summer daytime temperatures in two urban coastal CA air basins during 1948-2005: observations and implications Prof. Robert Bornstein Dept. of Meteorology, SJSU pblmodel@hotmail.com Bereket Lebassi, Jorge Gonzalez Dept. of Mechanical Engineering, SCU Presented at AMS Annual Meeting, Phoenix, AZ Jan 2009

2. 2 ACKNOWLEDGMENTS FUNDING PROVIDED BY: SANTA CLARA UNIVERSITY SANTA CLARA UNIVERSITY NSF NSF USAID USAID

3. 3 OVERVIEW BACKGROUND BACKGROUND DATA DATA ANALYSES ANALYSES RESULTS RESULTS –ALL OF CALIFORNIA –COASTAL VS. INLAND –UHI IMPACTS IMPLICATIONS IMPLICATIONS FUTURE EFFORTS FUTURE EFFORTS to appear, J. of Climate as Lebassi et al. (2009) to appear, J. of Climate as Lebassi et al. (2009)

4. 4 “The” research-problem What are the impacts of global climate change on CA What are the impacts of global climate change on CA –climate, e.g., seasonal and daily temperature trends –weather, e.g., precipitation and water supply –air quality, e.g., ozone and PM –energy planning, e.g., for peak usage –human health, e.g., UHI and thermal stress levels –agriculture, e.g., winery operations (Not covered in this paper) How can meso-met modeling best be used to (Not covered in this paper) How can meso-met modeling best be used to –reproduce past changes –estimate future trends

5. 5 Background (1 of 2) Global scale observations generally show past asymmetric (more for T min than for T max ) warming accelerated since mid-1970s on Global scale observations generally show past asymmetric (more for T min than for T max ) warming accelerated since mid-1970s on –global scale (1.0-2.5 deg resolution) (see graph) –regional scales Global-model results Global-model results –match the observations –predict accelerated further warming CA downscaled global-model results (see 2 nd graph) CA downscaled global-model results (see 2 nd graph) –have been done (at SCU & elsewhere) onto 10 km grids –show summer warming that decreases towards coast (but no cooling)

6. 6 Not much change from mid- 40s to mid-70s, when values started to again rapidly rise

7. 7 Statistically down-scaled (Prof. Maurer, SCU) 1950-2000 Summer (JJA) IPCC temp-changes ( 0 C) show warming rates that decrease towards coast; red dots are COOP sites used in present study & boxes are study sub-areas

8. 8 Background (2 of 2): Previous CA studies (next 2 slides) have explained their climate-change obs in terms of increased GHGs & increased: Coastal upwelling: Bakum (1990) Coastal upwelling: Bakum (1990) SSTs & urbanization: Goodridge (1991) SSTs & urbanization: Goodridge (1991) Cloud cover: Nemani et al. (2001) Cloud cover: Nemani et al. (2001) UHIs: Duffy et al. (2006) UHIs: Duffy et al. (2006) Irrigation Irrigation –Christy et al. (2006) –Bonfils and Lobell (2007) –Lobell and Bonfils (2008)

9. 9 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

10. 10 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 summer), 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

11. 11 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) NOTE: NOT A TOTALLY ORIGINAL IDEA 

12. 12 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 SUMMER (JJA) 1000-LST ERA40 1.4 DEG T-85 REANALYSIS SUMMER (JJA) 1000-LST –SEA-LEVEL PRESSURE TRENDS –FOR 1970-2005

13. 13 DATA ANALYSES Emphasis: on summer (JJA) data from 1970-2005 Emphasis: on summer (JJA) data from 1970-2005 All-CA warming/cooling trends calculated ( 0 C/decade) for: T max, T min T max -T min All-CA warming/cooling trends calculated ( 0 C/decade) for: T max, T min, T ave, & daily temp range (DTR = T max -T min ) Spatial-distributions of T trends: plotted for the Spatial-distributions of T max trends: plotted for the –South Coast Air Basin (SoCAB) –SFBA (includes northern Central Valley) Tests of statistical significance Tests of statistical significance Land-sea sea-level pressures Land-sea sea-level pressures –Spatial-distributions of 1979-2005 trends –Temporal-trends for sea-level pressure-gradient

14. 14 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 Results 1: SoCAB 1970-2005 summer (JJA) T max warming/ cooling trends ( 0 C/decade); ?=more data needed solid, crossed, & open circles show stat p-values < 0.01, 0.05, & not significant, respectively ? ? ?

15. 15 Results 2: SFBA & Central Valley 1970-2005 JJA T max warming/cooling trends ( 0 C/decade), as in previous figure ? ? ?

16. 16 GOES10 image of summertime marine Stratus penetration into Central Valley: supports our inland coastal cooling boundary (Leoncini, 2002)

17. 17 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 (IN LAST 2 GRAPHS) CURVE a: THUS ROSE AT MID RATECURVE a: T AVE THUS ROSE AT MID RATE Curve d: DTR (diurnal temp range) THUSCurve d: DTR (diurnal temp range) THUS DECREASED (AS T FALLS & T RISES) DECREASED (AS T MAX FALLS & T MIN RISES) Results 3: JJA Temp trends; all CA-sitesA B C D

18. 18 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 BUT T BUT T MAX – –HAS SLOWER RISE – –IT IS A SMALL DIFFERENCE B/T BIG POS-VALUE & BIG NEG-VALUE (AS SEEN IN ABOVE SPATIAL PLOTS) DTR ARE ALSO THUS “CONTAMINATED” T AVE & DTR ARE ALSO THUS “CONTAMINATED” NEXT 2 SLIDES THUS SHOWS SEPARATE TRENDS FOR CALIFORNIA NEXT 2 SLIDES THUS SHOWS SEPARATE TRENDS FOR CALIFORNIA –COASTAL AREAS –INLAND AREAS

19. 19 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 (EXPECT- ED) Curve b: T MIN IN- CREASED (EXPECT- ED) Curve c: T (UNEXPECTED), COULD BE DUE TO Curve c: T MAX FASTER RISE (UNEXPECTED), COULD BE DUE TOINCREASED>UHIs  DOWN-SLOPE FLOW 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

20. 20 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 COOLING (UNEXPECTED MAJOR RESULT OF STUDY) CURVE a: CURVE a: T AVE THUS SHOWED ALMOST NO CHANGE  AS FOUND IN LIT  AS RISING T & FALLING T  AS RISING T min & FALLING T max ALMOST CANCELLED OUT Curve d: DTR THUS DE- CREASED, AS  T  T MIN ROSE &  T FELL  T MAX FELL a b c d

21. 21 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: both strengthened & moved to NW (can’t see here) H & L: both strengthened & moved to NW (can’t see here)

22. 22 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 previous Fig. These stronger HPGFs  stronger sea breezes  coastal cooling

23. 23 IPCC 2001 does show cooling over Central California!!

24. 24 Significance of above Coastal-Cooling and Inland-Warming trends CA ASSYMETRIC WARMING IN LITERATURE IS HEREIN SHOWN TO BE DUE TO CA ASSYMETRIC WARMING IN LITERATURE IS HEREIN SHOWN TO BE DUE TO –T –COOLING T MAX IN COASTAL AREAS & –CONCURRENTT –CONCURRENT WARMING T MAX IN INLAND AREAS PREVIOUS CA STUDIES PREVIOUS CA STUDIES –DID NOT LOOK SPECIFICALLY AT SUMMER DAYTIME COASTAL VS. INLAND VALUES HAVE –THEY THUS REPORTED CONTAMINATED T, T, & DTR VALUES –THEY THUS REPORTED CONTAMINATED T MAX, T AVE, & DTR VALUES –THEY, HOWEVER, ARE NOT INCONSISTENT WITH CURRENT RESULTS, THEY ARE JUST NOT AS DETAILED IN THEIR ANALYSES & RESULTS

25. 25 Result 7. JJA 1970-2005 2 m T max trends for 4 pairs of sites: urban (red, solid) & rural (blue, dashed) Notes: 1.All sites are near cooling-warming border 1.UHI-TREND (K/decade) = absolute sum b/t warming-urban & cooling-rural trends a. SFBA sites a. SFBA sites > Stockton > Stockton (0.38 + 0.17 = 0.55) (0.38 + 0.17 = 0.55) > Sac. (0.49) b. SoCAB sites b. SoCAB sites > Pasadena (0.26) > Pasadena (0.26) > S. Ana (0.12) > S. Ana (0.12) u r

26. 26 Notes on JJA daytime UHI-trend results Faster growing cities (area & population) had faster growing UHIs (not shown) Faster growing cities (area & population) had faster growing UHIs (not shown) As no coastal sites showed warming T values, calculations could only be done at As no coastal sites showed warming T max values, calculations could only be done at –these four pairs –Located at the inland boundary of the warming and cooling areas Coastal sites would have cooled even more without their (assumed) growing UHIs Coastal sites would have cooled even more without their (assumed) growing UHIs

27. 27 SUMMARY OF CURRENT CA OBS SUMMER T min IN CALIF HAVE BEEN WARMING FASTER THAN T max SUMMER T min IN CALIF HAVE BEEN WARMING FASTER THAN T max SUMMER DAYTIME T max HAVE BEEN COOLING, IN LOW-ELEVATION COASTAL AIR-BASINS SUMMER DAYTIME T max HAVE BEEN COOLING, IN LOW-ELEVATION COASTAL AIR-BASINS THE FOLLOWING AREAS ARE COOLING IN CENTRAL CA: THE FOLLOWING AREAS ARE COOLING IN CENTRAL CA: –MARINE LOWLANDS –MONTEREY –SANTA CLARA VALLEY –LIVERMORE VALLEY –WESTERN HALF OF SACRAMENTO VALLEY

28. 28 Current results are unique, as this study is first to: segment obs in all the following ways segment obs in all the following ways –summer-values only –T & T, as well as T –T max & T min, as well as T ave –coastal vs. inland sites consider sea-breeze enhancement consider sea-breeze enhancement –as causal mechanism of climate change –instead of: GHGs, irrigation, SST, UHI, PDO, &/or aerosols (next slide) do data analyses & urbanized meso-met modeling (not shown) do data analyses & urbanized meso-met modeling (not shown)

29. 29 Possible explanations of coastal cooling in the literature GHG warming: GHG warming: –triggers secondary “reverse reaction” local effects –e.g., increased sea breeze activity (our contention) UHI development: warms (& not cools) UHI development: warms (& not cools) SST changes: SST changes: –GHG warming off Calif.-coast is stronger than increased upwelling, as –SSTs are increasing (not shown) PDO: uncorrelated to T max (not shown) PDO: uncorrelated to T max (not shown) Increased rural-irrigation: Increased rural-irrigation: –cools T max –important in Central Valley

30. 30 BENEFICIAL IMPLICATIONS OF COASTAL COOLING NAPA WINE AREAS NAPA WINE AREAS –MAY NOT GO EXTINCT –REALLY GOOD NEWS! (next map) ENERGY FOR COOLING ENERGY FOR COOLING –MAY NOT INCREASE AS RAPIDLY AS POPULATION –PAPER J21.4, THIS SESSION BY GONZALEZZ ET AL. LOWER HUMAN HEAT-STRESS RATES LOWER HUMAN HEAT-STRESS RATES O 3 CONCENTRATIONS MIGHT CONTINUE TO DECREASE, AS LOWER T max REDUCES O 3 CONCENTRATIONS MIGHT CONTINUE TO DECREASE, AS LOWER T max REDUCES –ANTHROPOGENIC EMISSIONS –BIOGENIC EMISSIONS –PHOTOLYSIS RATES

31. 31 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

32. 32 GOOD IMPLICATIONS FOR O GOOD IMPLICATIONS FOR O 3 PAST & PROJECTED SFBA & SoCAB O 3 DECREASES MAY PAST & PROJECTED SFBA & SoCAB O 3 DECREASES MAY – IN-PART BE DUE TO DAYTIME T max COOLING- TRENDS and – NOT ONLY TO REDUCED ANTHROPOGENIC EMISSIONS RECENT CARB AQMSs RECENT CARB AQMSs – HAVE NOT REPRODUCED FULL RATE OF OBSERVED O-DECREASE OBSERVED O 3 -DECREASE – MAYBE (IN PART) DUE TO THIS UNMODELED COOLING TREND

33. 33 Future Coastal-Cooling Efforts (PART 1 OF 2) EXPAND (TO ALL OF CA & beyond) EXPAND (TO ALL OF CA & beyond) –ANALYSIS OF OBS (IN-SITU & GIS) –URBANIZED MESO-MET (MM5, RAMS, WRF) MODELING SEPARATE INFLUENCES OF CHANGING (via uRAMS modeling in SCU PhD of B. Lebassi): SEPARATE INFLUENCES OF CHANGING (via uRAMS modeling in SCU PhD of B. Lebassi): – LAND-USE PATTERNS AGRICULTURAL IRRIGATION AGRICULTURAL IRRIGATION URBANIZATION URBANIZATION –SEA BREEZE: INTENSITY, FREQ, DURATION, &/OR PENETRATION

34. 34 POSSIBLE FUTURE EFFORTS (PART 2 OF 2) DETERMINE POSSIBLE “SATURATION” OF SEA- BREEZE EFFECTS FROM DETERMINE POSSIBLE “SATURATION” OF SEA- BREEZE EFFECTS FROM –COLD-AIR TRANSPORT –STRATUS-CLOUD EFFECTS ON LONG- & SHORT-WAVE RADIATION DETERMINE CUMULATIVE FREQ DISTRIBUTIONS OF T VALUES, AS DETERMINE CUMULATIVE FREQ DISTRIBUTIONS OF T MAX VALUES, AS –EVEN IF AVERAGE T DECREASES, –EVEN IF AVERAGE T MAX DECREASES, –EXTREME VALUES T MAY STILL INCREASE (IN INTENSITY &/OR FREQUENCY) –EXTREME VALUES T MAX MAY STILL INCREASE (IN INTENSITY &/OR FREQUENCY) DETERMINE CHANGES IN LARGE-SCALE ATM FLOWS: DETERMINE CHANGES IN LARGE-SCALE ATM FLOWS: –HOW DO GLOBAL CLIMATE-CHANGE EFFECT POSITION & STRENGTH OF: PACIFIC HIGH & THERMAL LOW? –THESE TYPES OF CLIMATE-CHANGES ARE THE ULTIMATE CAUSES OF LOCAL TEMP & PRECIP CHANGES

35. 35 Cooling summer daytime temperatures in two urban coastal CA air basins during 1948-2005: observations and implications Prof. Robert Bornstein Dept. of Meteorology, SJSU pblmodel@hotmail.com Bereket Lebassi, Jorge Gonzalez Dept. of Mechanical Engineering, SCU QUESTIONS?