Global Warming and Hurricane Activity and the Impact on U.S. Transportation

Dr. Douglas A. Stewartand

Dr. Lee E. Branscome

Climatological Consulting CorporationPalm Beach Gardens, Florida

Factors Influencing Hurricane…

Is Global Warming Linked to Hurricane Activity?

•Formation frequency•Geographical distribution

•Size•Rainfall

•Modeling studies

•Empirical studies

•Natural variability

Impact on Transportation Infrastructure

•The linkage debate

•Metrics of activity

•Intensity

Hurricane intensity

28 30 32 34800

820

840

860

880

900

920

28 30 32 34

120

140

160

180

200

220

SST (deg C)

VmxPf

Emanuel’s MPI(Emanuel 1986,1987,1991)

Holland’s MPI(Holland 1997)

•Underlying SST•Depth of warm water•Wind shear

•Upper level disturbances•Eye wall replacement cycles•Lateral moisture flux

Maximum Potential Intensity (MPI) Theory

Hurricane formation frequency

•Favorable environment (SST, low wind shear, deep moist layer)•Incipient disturbance of independent origin

Emanuel’s genesis index (http://wind.mit.edu/~emanuel/gindex.htm )

G.I.=|105|3/2(H/50)3(Vp/70)3(1+0.1Vs)-2

•Distance from equator (Coriolis effect to induce rotation)

=Absolute vorticityH=600mb R.H.

Vp=potential wind speed (MPI)Vs=wind shear |v850-v250|

Geographical distribution of hurricanes

•Characteristics/locations of incipient disturbance (e.g., frontal perturbation, easterly wave)

•Quasi-stationary large-scale circulation features•Spatial distribution of SST anomalies

(http://www.tpc.ncep.noaa.gov/tracks)

1995: 19 named storms 2004: 15 named storms

NAO Effect

•NAO Patterns for July and October (+ phase)

•Tropical cyclones during NAO extremes (monthly NAO data from 1950-2005)

10% of storms @ max (-) NAO index10% of storms @ max (+) NAO index

1950 1960 1970 1980 1990 2000

•Monthly NAO index averaged over individual hurricane seasons

ENSO EffectTropical cyclones during ENSO extremes Multivariate ENSO Index data from 1950-2005 (NOAA-CIRES CDC)HURDAT best track data from 1950-2005

•Monthly ENSO index averaged over individual hurricane seasons

1950 1960 1970 1980 1990 2000

25% of storms @ max (+) ENSO index 25% of storms @ max (-) ENSO index

10% of storms @ max (+) ENSO index 10% of storms @ max (-) ENSO index

Hurricane size

•Radius of maximum winds (RMW); cloud shield

(http://www.tpc.ncep.noaa.gov)

Charley 2004: Cat 4 Wilma 2005: Cat 3

•Historical database on RMW is limited in quantity and quality

NCDC image, courtesy Dr. Jack Beven (http://www.mindspring.com/~jbeven/intr0012.htm)

•Some damages from small stormsAndrew: cat 5 (35.9B); Charley: cat 4 (15.4B); Camille: cat 5 (7.5B)

(adjusted to 2005 dollars)

•Some damages from large stormsFrances: cat 2 (9.1B); Jeanne: cat 3 (7.1B); Floyd: cat 2 (5.1B)

Katrina: cat 3 (e75B); Rita: cat 3 (e10B); Wilma: cat 2 (e12.2B)

•Factors governing hurricane size largely unknown•More observations, theory and hi-res modeling needed

(adjusted to 2005 dollars)

Impacts from large and small storms

Hurricane rainfall

•Large hurricanes produce more rainfall than small•Slow moving storms produce more rainfall locally •10-15 inches not uncommon (Mitch (1998) produced 25 inches in 36 hours in southern Honduras)•Tropical storms may be copious rain producers (Claudette, 1979 produced 45 inches near Alvin, TX; Allison, 2001 produced > 30 inches on parts of Houston.TX)•Local topography may result in flash flooding (often contributing to the majority of fatalities)•City drainage easily overwhelmed in flat coastal regions

•Increased hurricane rainfall likely

From modeling studies…as high as 40% increase for intense storms(Gutowski, 1994) and 18% increase for storms within 100 km of center(Knutson and Tuleya, 2004) are estimated in a doubled CO2 climate]

•Limited historical data on hurricane rainfall amounts•Estimates from radar and satellite are for limited samples only

Changes in a warming climate?

Is global warming influencing hurricane activity ?

Hybrid Models

•Hi-res hurricane simulations with CGM BCs•Ignores genesis frequency issues•Tests MPI theory•Rainfall sensitivity

Empirical Studies

•Cyclone activity metrics over period of record•Secular trend vs. natural variability•Limited records- statistical significance issues•Non-uniformity of measurement methods•Tests MPI theory•Stimulates further theoretical inquiry

•Hurricane activity in control vs. warm climate simulations•Conflicting results in hurricane frequency •Problems with simulating hurricanes and their genesis•Some robust results

Coupled Global Models (CGM)

Hybrid Model StudyKnutson and Tuleya (2004)- J. Climate

Do models show increased hurricane intensity and rainfall in a warmer climate?

•Temperature and moisture profiles and SST from 9 CGMs used as background•Simulate control climate and warm climate (1% CO2 increase/yr) •~1300 5-day idealized hurricane simulations with the GFDL hurricane model

•14% increase in central pressure fall•6% increase in max surface winds•18% increase in precipitation within 100 km of center•2x increase in cat-5 storm probability

Cat 3 Cat 5 Cat 4

Hurricane intensity distribution: Aggregate results

Minimum central pressure (mb)

(3 ocean basins (ATL,WPAC,EPAC); 4 convective parameterizations)

Empirical StudyTrenberth (2005)- Science

Look for trends in Atlantic SST and hurricane activity [Accumulated Cyclone Energy Index]

(ACE= sum of Vm2 over cyclone lifetime for all storms in a season)

SST over Atlantic basinfrom 1870-2004

Annual ACE variability from 1950-2004.

Empirical StudyEmanuel (2005)- Nature

Trends in Atlantic and Pacific SST and hurricane activity [Power Dissipation Index]

(PDI= sum of Vm3 over cyclone lifetime for all storms in a season)

ATL

WPAC

ATL+WPAC

Empirical StudyWebster et al. (2005)- Science

Trends in cyclone number, duration and intensity in a warming environment (satellite era only; 1970-2004)

•6 ocean basins: NATL, WPAC, EPAC, SPAC, NIO, SIO•No distinct secular trend in storm numbers or duration, globally•Only secular trend in number and duration is in the NATL basin•No trend in maximum wind speed of hurricanes•Distinct secular trend in number of intense hurricanes, globally

ATL Hurricane Activity Metrics (HURDAT 1870-2005)

% o

f m

ed

ian # StormsACE

PDI

Storm Days

1870 20051950

# cat-3,4,5

1870 20051950

Cat-4,5/hur

%%

of

med

ian

% o

f m

ed

ian

% o

f m

ed

ian

Num

ber

ATL SST variability

ATL SSTA

1870 20051950

All (TS + H)

Major H

% o

f m

ed

ian

% o

f m

ed

ian

Storm numbersStorm durationU.S. Landfalls

Global Warming->Increased Hurricane Activity?

•Peer-reviewed studies establish a link between increased hurricane intensity and increased SST (Trenberth, 2005; Emanuel, 2005; Webster et al., 2005)

•Warming SST attributed to increased greenhouse gas emissions (IPCC,2001)

•Skeptics claim:

•The skeptics choose the press rather than the scientific peer-review process

•No trends, only multi-decadal fluctuations•SST signal part of the natural variability•Past data are erroneous•Land-falling storms do not support linkage•Metrics of hurricane activity are misleading

•There are still many unknowns

•Why 80-90 global hurricanes/yr and not 25 or 200?•Why do storm numbers decrease while intensities increase in most basins? •What is the role of hurricanes in the global heat redistribution?

Impact on Transportation Infrastructure

Increased risk of:

•Surge and wave damage to ports, bridges, coastal airports and highways

•Inland wind/rain damage:

•Orlando Int. Airport’s damage from Charley, Frances, Jeanne (2004); Homestead Airport destruction from Andrew (1992)•Traffic signals/sign destruction

•Adverse impacts on fuel costs and availability:

•Damage to offshore drilling platforms and coastal refineries•Energy price shocks from more frequent threats

Significant impact on infrastructure:

•Greater Likelihood of wind/flood/surge damage over the lifetime of the structure.

•Location of new infrastructure will require higher elevations

(Elevation 9 ft)