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Bereket Lebassi Habtezion Ph.D. Candidate Department of Mechanical Engineering

Bereket Lebassi Habtezion Ph.D. Candidate Department of Mechanical Engineering Santa Clara University Prof. Jorge Gonzalez Advisor Department of Mechanical Engineering City College Of New York Presented at Santa Clara University Dissertation defense on 9 June 2010.

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Bereket Lebassi Habtezion Ph.D. Candidate Department of Mechanical Engineering

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  1. Bereket Lebassi Habtezion Ph.D. Candidate Department of Mechanical Engineering Santa Clara University Prof. Jorge Gonzalez Advisor Department of Mechanical Engineering City College Of New York Presented at Santa Clara University Dissertation defense on 9 June 2010 Observational and Modeling Study of Urbanization vs. Global Warming Impacts on SoCAB and SFBA Climate

  2. Outline • Background and Hypothesis • Observational Study • SFBA and SoCAB analysis • Impacts on Energy • Simulation Setup • Grid Configuration • Land Use input • Anthropogenic heating • Results & Validation • GHG impacts • Urbanization impacts • Conclusion

  3. Motivation 1: GHG Global-Warming • Earth has warmed approximately 0.2 oC/decade for past 30 years, with max • warming after 1970 • Land temps has warmed faster than SSTs From NASA RESEARCH NEWS (2006), group led by James Hansen, GISS, NYC

  4. Motivation 2: Interaction of coastal climate influences • Global • Sea surface temps (SSTs) • Ocean currents • General Circulation (GC) pressure systems • Mesoscale • Sea/land breezes • Mt/valley breezes • Ocean upwelling • Land-use &/or Land-cover (LULC) changes • Urban heat islands (UHIs)

  5. Earlier studies have related climate-change to increased (*=CA studies; modeling studies in yellow): • SSTs, evap rate: *Goodridge ‘91, Karl et al. ‘93 • Cloud cover changes: *Nemani et al. ’01 • Upwelling: *Bakun ‘90,*Snyder et al. ‘03; McGregor et al. ‘07 • Anthropogenic land cover conversions:Pielke et al. ’07, Chase et al. ‘00; Mintz ‘84; Zhang ‘97 • Irrigation: *Christy et al. ’06, Lobell et al. ’06, *Kueppers et al. ’07, *Bonfils et al. ’07 • GHGs: *Duffy et al. ’06, Walters et al. ’07, Cayan et al. ‘08 • UHIs: Ladochy et al. ’07

  6. Research questions: the relative contributions to observed temperature-trends in coastal-urban areas from GHG-warming &/or LCLU-changes? • 1. In urban coastal regions, what temperature-change is due to each of the following: • GHG-induced global climate-change • urbanization (i.e., LULC-changes) • 2. How do these temperature-changes influence coastal-flows

  7. Current Hypothesis: Observed Calif temp trends resulted from • GHG WARMING/LULC and/or • b. INCREASED INLAND WARMING • INCREASED HORIZONTAL T- & p-GRADIENTS • (COAST TO INLAND) • INCREASED SEA BREEZE FREQ, INTENSITY, • PENETRATION, &/OR DURATION  • COASTAL REGIONS DOMINATED BY SEA BREEZES SHOULD THUS COOL DURING SUMMER DAYTIME PERIODS

  8. DATA • NCDC DAILY MAX & MIN 2-METER TEMPS FROM 273 CALIF SITES (see map below) FROM 1948-2005 • NCDC MEAN MONTHLY GRIDDED SSTs • INTERNATIONAL COMPREHENSIVE 0CEAN-ATM DATA SET (ICOADS) • 2 OR 1 DEG HORIZ RESOLUTION • SCU DOWNSCALED REGIONAL CLIMATE CHANGE MODELING RESULTS FOR CALIF (10 KM RESOLUTION) FOR 21ST CENTURY (see same map below)

  9. ANALYSES • Only data from 1970-2005 (due to its accelerated warming) were used • Annual & summer (JJA) warming/cooling trends calculated (0C/decade) for SST, Tmax, Tmin • Spatial distributions of JJA Tmax trends plotted for • South Coast Air Basin (SoCAB) • SFBA and Central Valley (CV) • JJA land-sea T-gradient (as surrogate for p-gradient) trends calculated from • mean monthly SSTs • 2-m land Tmax values

  10. SCU (Maurer 2007) statistically 10-km downscaled 1950-2000 modeled JJA temps (0C) show total warming rates that decrease to coast (dots are Calif NCDC sites & boxes are study sub-areas)

  11. Result 1: Lebassi et al. (2009) J. of Climate Observed 1970-2005 CA JJA max-Temp (0C/decade)trends in SFBA & SoCAB show concurrent: > low-elev coastal-cooling & > high elev & inland-warming > signif levels: solid circles >99% & open circles <90%)

  12. Results 2: Same for SFBA & Central ValleyCOOLING AREAS: MARIN LOWLANDS, MONTEREY, SANTA CLARA V., LIVERMORE V., WESTERN HALF OF SACRAMENTO V.

  13. Results 3: Temp. trends for all of California Tmin (Curve b) increasing faster than Tmax (Curve c)

  14. Result 4: Combined SFBA & SoCAB 1970-2005 summer trends (oC decade-1) of Tmax (Curves c) Inland Tmaxwarming sites Coastal Tmaxcooling sites (a) (b) (c) (d)

  15. Result 5: Average JJA 1.4-deg ERA40-reanalysis SLP trends (hPa/decade) at 11 LT for 1970-2005 - • As Temp-grad is only a surrogate for p-grad,… • Arrow shows SLP-gradient calc. end-points • Plus & minus are High- & Low-pressure centers, respectively. • p-increases (up to 0.34 hPa decade-1) in Pacific High • p-decreases (up to -0.8 hPa decade-1) in Calif- Nevada thermal Low • p-gradient trend in next slide + +

  16. Result 6: Trend in ocean-land summer SLP-gradient (hPa 100-km-1 decade-1) at 11 LT at end-points in previous slide Results show: p-gradient increases in both areas  increased sea breeze

  17. Result 7: Implications of max-Temp trend on Calif energy-usageLebassi et. al (2010) J. of Solar Energy and Engineering (a) Cooling Degree Day (CDD) trend: upward due to GHG warming  More energy for cooling (b) Heating Degree Day (HDD) trend: downward due you to GHG warming  Less energy for heating

  18. SUMMARY 1: OF OBS STUDY • SUMMER DAYTIME MAX-TEMPS HAVE • COOLED IN LOW-ELEVATION COASTAL AREAS • WARMED IN INLAND AREAS • PREVIOUS STUDIES DREW WRONG CONCLUSIONS B/C • They did not separate summer vs. winter, day vs. night, &/or inland vs. coastal • Therefore, their Tmax were wrong and thus their Tave & DTRs were also contaminated

  19. Modeling Effort Introduction to Regional Atmospheric Modeling System (RAMS)

  20. RAMS RANS (non-transformed) Equations Km, h: eddy diffusivity coef. for momentum & heat. Momentum eqs for u, v & w (1) (2) (3) Latent heat & RFD Local ∆ = Advection + p-grad + Coriolis + Turbulent Diffusion Thermodynamic Eq for ice-liquid water potential-temp Water Species (n-species, e.g. vapor, ice, snow, …) Sources & sinks via phase changes

  21. Pressure Eq (in terms of π) (4) (5) (6) (7) Exner function π, for pressure Ideal Gas Law for density Poisson eq for Tv • In summary: • Prog Eqs for u, v, w, өil, rn, π′ • Diag Eqs for π, ρ, p, Tv

  22. Vertical Diffusion Coef Km,h,e via TKE (e) Shear Production Buoyancy Molec Dissipation Sm,h,e are f(Ri) l is mixing length

  23. Vertical Boundary Conditions • z= H (model top) = 18.8 km • Rigid lid, with Rayleigh friction layer of 4 km • w = 0 • z= h (SBL top) = 50 m • Continuity of fluxes, gradients, & profiles • z= 0 (sfc) • Sfc energy balance Eq in LEAF3 • No slip BC: V = 0 • z=Hs (bottom soil layer) = 1 m • Constant temperature from large scale model

  24. Sfc BC for T(t): RAMS uses LEAF-3 “big leaf” model to solve sfc energy balance at each sfc-type, e.g., for all-urban sfcs (no veg or evaporation) • Terms on RHS of eq (L to R): • ↓ solar rad absorbed at sfc • ↓IR rad from atm absorbed at sfc • ↑IR rad from sfc to atm • ↑IR rad from urban sfc • Note: rad terms come from complex rad-transfer model • convective heat to atm [where ( )* quantities come from SBL-Eq ] • ground heat to atm (where өs comes prog soil temp Eq) • anthro heat to atm. (specified, in slide below) • Finally: sum of RHS terms yields trend of building-canopy temp θu, which when added to past-value gives current-value.

  25. Parameter-values (needed as input in previous Eq) for different urban classes where α Albedo ε Emissivity FV Vegetation Fraction HV Vegetation/building Height

  26. Set up of RAMS simulations of SoCAB Area

  27. Selected past (1966-70) & present (2001-2005) simulation-periods: have similar PDO- & temp-variations  large-scale variability effects are eliminated Note: ENSO summer-impacts are mainly in winter in study-area

  28. Simulation Determination • Research goal: separate-out effects of urbanization & GHG warming • on observed Lebassi et al. (2009) SoCAB JJA max-temp trends • use RAMS to simulate these changes • RAMS simulations • Runs 1 vs. 2: • Research question: Effects of global climate-change? • Run 1: current • urban LULC (NOAA 2002) at 30-m resolution • global-climate & SSTs for five JJA-periods (2001 to 2005) • Run 2: uses • Run 1 (Current 2002) LULC • global climate & SSTs for five past JJA-periods (1966 to 1970) • Runs 1 vs. 3: • Research question: Effects of urbanization? • Run 1: one-year of Run 1 (2002) • Run 3: pre-urban • LULC: all urban turned to local dominant-class, i.e., scrubland • over-estimate of max-urbanization effects • 2002 JJA global-climate & SSTs

  29. ICs and Large-scale BCs (FDDA) • Model initialized • 0000 UTC = 17 LT • 1 June of given year • 12-hr spin up: 1st night • Large scale BCs • every 6-hr • from gridded NCEP global-model output

  30. Grid Configuration • > Arakawa-C staggered grid • Horiz nested-grid resolution • Grid 1: 20 km • Grid 2: 4 km • Vertical Grid >49 levels to 31 km • Δz = 40 m (near sfc) • 1.15 stretch-ratio • Δz =1.2 km (aloft)

  31. + + + + • Grid 2 (4 km): present (2002) LULC-classes • Lines: key topographic-heights (+ = peaks) • Input: 30-m NOAA C-CAP LULC  RAMS’s Leaf-3 classifications • Output colors: dominant class; parameter values as weighed averages • Veg: greens • Urban: browns • Black squares: METAR stations for RAMS evaluation

  32. Model-Evaluation with Run-1 (current met & LU) output: June 1-10, 2002; averages of 12 SoCAB METAR sites where: blue is obs & red is closest RAMS grid point Mean wind speeds: both at 10-m Mean temps: both at 2-m model =3.1 m/s vs. obs = 2.9 m/s model = 20.2oC vs. obs = 19.3oC

  33. Model-Evaluation (cont.) • Current-period evaluation • (previous slide): • Temp: r2 = 0. 87 (blue) • Speed: r2 = 0.82 (red) a • Past-period evaluation: • 1970 JJA-average • daily-Tmax • average of 15 COOP-sites • Model (red) minus • Obs (blue) • Tmax ave-diff = 0.7oC b • Correlation (for part-b): • r2 = 0. 70 c

  34. RAMS Results:19-m spatial-patterns in following order Temp- and wind-results from • Run 1: current climate and current urbanization • Run 2: past climate and current urbanization • Run 1 minus Run 2 • Run 3: current climate and no-urbanization • Run 1 minus Run 3

  35. Large scale BC inputs into RAMS (next 5 slides)

  36. H H L L Now Past • NCEP SLP: 17-LT JJA (5-yr Ave) • Orig. SLP-resolution: 2.5 deg • Top R: Run-2 (P); Top L: Run 1 (N) • Lower: Run-1 minus Run-2 (N-P) • Box: area of p- grad calculation • Results: Location of H: not much change • Mag: diminished over most of ocean • Peak-decreases: over center of H • Increases found: N & S of decrease area • Max-decrease over Mx-coast (our D-2) • due to expansion of Thermal- L over land + - - + N- P

  37. H H C C Now Past Present & Past 17-LT JJA-Ave NCEP 1000-hPa T(oC) • Area is black-box sub-area of previous slide • BC input to RAMS: every 6-hr for periods of Run-1(N) & Run-2 (P) • White boxes: D-1 & D-2 • Both results: Hot inland (H) & Cool ocean (C) • Comparison: H & C centers: moved to SE • Changes: best seen in next slide

  38. N - P N - P + + - - Present minus Past 17-LT JJA-Ave NCEP 1000-hPa ΔT(oC) T(oC) • Right slide: horizontal section • Area is same as previous slide • Boxes: again D-1 & D-2 • Dash-line: z-section for slide at right • Results:Inland warming (+) & • off-shore cooling (-) protrudes into D-2 • Left Slide: vertical section (from Fig. on right; topo not shown) • Violet-line: land-area • Green line: D-1; White-line: D-2 • Results: • Max warming: at 350-hPa or 1.6km • Cooling: up to 980-hPa (= 400-m) • Note: cooling-area is b/t coast & center of H (to West) and in the area of falling-SLP of previous slide (more below)

  39. Now Past • ICOADS BC-SST: input to RAMS • Box is D-2 • RAMS-interpolated D-1: JJA 5-yr ave. • (constant for a given summer) • Top L: Run-1 (N) orig.-resolution: 1 deg • Top R: Run-2 (P) orig- resolution: 2 deg • Lower: Run-1 minus Run-2 SST(N-P) • Large-scale SST results: • NW-cooling in D-1 is a large-scale effect • max-warming in south N- P T(oC)

  40. RAMS GHG-WARMING RESULTS:NEXT 8-SLIDES

  41. 12 LT 14 LT • RAMS Run-1 (present) JJA-ave. D-1 T(oC) & V (barb = 1 m/s); Box is D-2 • Results: • Cool: ocean, coastal, & Mt. areas • Warm: inland • 12 LT: SB- & upslope-flows started • 14 LT: Both flows: more-developed • 16 LT: combined SB- & upslope- • flows 16 LT

  42. Interpretation of sea-breeze wind-vector differences plots Acceleration case: N > P, so N-P is in their dir (on-shore) Retardation case: P > N, so N-P is in opposite dir (off-shore) N -P N N-P P -P P N-P where: N = current wind-vector (red) P = past wind-vector (black) C-P = current minus past (white)

  43. 14 LT 12 LT • RAMS Run-1 (present, prev. slide) • minus Run-2 (past) JJA-Ave D-1 • T(oC) & V (barb=0.4 m/s); Box is D-2 • Results: • Ocean warming < inland warming • 12 LT: coastal-cooling started; SB-change not evident in D-2 • 14 LT: coastal-cooling fills basin N-S & SB-change still not resolved in D-2 • 16 LT: coastal-cooling reaches max & SB starts to weaken!! 16 LT

  44. D-2 JJA-Aver ∆T(oC) & ∆V • (barb = 0.5 m s-1) • Results (relative to D-1): • More details & stronger • temp & flow effects • 12 LT: SB better defined • & coastal-cooling is in 2-parts • 14 LT: SB acceleration now visible & coastal- cooling is seen as stronger N of city • 16 LT: SB starts to slow offshore, but is still accelerating over city • Peak coastal-cooling over 35-years of about 1.0 oC matches observed trend of 0.3 oC/decade • Dashed-line is for subsequent z-section 12 LT 14 LT 16 LT

  45. Two-tailed stat. sig. values for T, U, & V U T 12 LT V 14 LT 16 LT • ∆T: coastal-cooling, SST-change, & inland-warming are mostly significant at >99% (grey); less-significant (<90%, yellow) results are due to cancellation of GHG-warming by increased marine-flow cooling • ∆U & ∆V: Most changes also significant at 99%; less-significant areas are over ocean at 12 LT when SB change is not strong & over land at 14 LT when SB starts to weaken

  46. Past Now • z-section at 33.85 N for • T(oC) & (u, 100w) wind (m/s) • Top R Run-1 (Now): NCEP cold-area to 500-m; warmest inland; inversion top 900-m & base 50-m • Top L Run-2 (Past): inversion top now 750-m & inversion-base at sfc • Bottom R Run-1 (N) minus Run 2 (P): • > Present w-wind: up in cooling area & down above • > GHG-induced warming aloft & inland • > Shallow warming over ocean from SST increases • > NCEP-cooling over ocean & sea-breeze induced cooling over previously-warm coastal land-area (both to about 500-m) • z-line is eastern-edge of subsequent w-section N - P T(oC)

  47. Stat. sig. for previous z-section at 33.83 N for temp-changes of Domain-2 • SST warming, cooling over ocean aloft, & coastal cooling: all significant at > 99% • transition zone is less significant • Note: topography not shown

  48. Now Past • z-section w (cm/s) at 14 LT • Top L: Run-1 (Now): Subsidence over ocean & up-motion max over-peaks • Top R: Run-2 (Past): Patten similar to Run-1, but up-motion was stronger • Bottom R: Run-1 minus Run-2 (N-P) • > Subsidence decreases (less negative, yellow) over ocean, as thermal-L expansion weakens Pacific-H • > The area of decreased up-motion (less positive, blue) is due to increased marine-air stability and is bisected by a narrow area of increased (yellow) up-motion, as topo-graphic-induced up-motion overcomes stability effect N-P

  49. URBANIZATION RESULT (one slide): 2002 JJA 12, 14 & 16 LT Run 1 (Urban) minus Run 3 (no-Urban): Temp & U (1 barb = 0.5 m/s) differ-ences (U minus no U) 12 LT • Urban areas: • UHI-peaks at 16 LT (1.0 oC) • SB-retardation peaks (1.5 m/s) at 16 LT (Run-1 vector onshore & difference-vector offshore) due to urban z0-deceleration • Rural: • small inland-directed warm-air advection (0.2 oC) • insignificant Mt-top & over-ocean cooling (secondary-circulation effect?) • Costal park-insert shows SB induced-cooling w/o the retardation-effect 14 LT 16 LT T (oC)

  50. Summary The effects of urbanization & GHG- warming on summer sea breezes in the SoCAB were studied by > RAMS meso-met modeled PBL winds & temps > comparison of RAMS temps with observed near-sfc values • Increased GHGs (Run-1 vs. Run-2) resulted in > increased sea-breezes over the ocean & coastal plain, and thus > sea-breeze induced coastal-cooling over the coastal plain (whose aerial extent & magnitude matched the observations) • Urbanization produced and > UHI and a > reduced sea-breeze penetration (due to the large urban-z0) • Implications from coastal-cooling > Lower energy-use for cooling > Lower heat-stress levels > Lower peak O3 concentrations > Benefits for peak-temperature sensitive agriculture

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