Hurricane As an Extreme Meteorological Event

CHAPTER 42 HURRICANE AS AN EXTREME METEOROLOGICAL EVENT ROGER A. PIELKE, JR. AND ROGER A. PIELKE, SR. 1 INTRODUCTION: UNDERSTANDING SOCIETAL RESPONSES TO EXTREME WEATHER EVENTS In the 1970s, many decision makers became increasingly interested in climate because of numerous weather-related impacts around the world. Events that helped to stimulate this interest included the failed Peruvian anchovy harvest in 1972 and 1973, the 1968 to 1973 drought in the African Sahel, a severe winter freeze in 1972 in the Soviet Union, and in 1974 floods, drought, and early frost in the U.S. Midwest. In 1977, winter in the eastern United States was the coldest ever recorded and summer was one of the three hottest in a century. As a consequence of these extreme events and their impacts, decision makers began paying more attention to the relation of weather and climate to human affairs. Understanding societal responses to weather and climate requires an understanding of the terms weather and climate. The 1979 World Climate Conference adopted the following definitions of weather and climate: Weatheris associatedwith the completestate of the atmosphereat a particularinstant in time, and with the evolutionof this statethrough the generation,growth and decayof individual disturbances. Climateis the synthesisof weatherevents over the whole of a period statisticallylong enoughto establishits statisticalensemble properties (mean value, variances,prob- abilities of extremeevents, etc.) and is largely independentof any instantaneousstate. Handbook of Weather,Climate, and Water:Atmospheric Chemistry, Hydrology, and Societal Impacts, Edited by ThomasD. Potter and BradleyR. Colman. ISBN 0-471-21489-2 (g) 2003 John Wiley & Sons,Inc. 789 .. 790 HURRICANE AS AN EXTREME METEOROLOGICAL EVENT Climate refers to more than "averageweather" (Gibbs, 1987). Climate is, in statisticalterminology, the distribution of weatherevents and their componentprop- erties (e.g., rainfall) over someperiod of time, typically a few monthsto thousands of years. In general,climate statisticsare basedon actual(e.g., weatherstation) or proxy (e.g., ice core) records of weatherobservations. Such a record of weather events can be used to create a frequency distribution that will have a central tendency,which can be expressedas an average,but it will also have a variance (i.e., spreadaround an average).Often, variability is more important to decision makersthan the averagestate (Katz and Brown, 1992). How society thinks about "extreme" weatheris, of course,related to what is defined as "normal" weather.What, then, is a "normal" weatherevent? There are different ways to define normal weather.Of course,it is possibleto argue that on planetEarth all weatherevents are in somesense normal; however,such a definition has little practical utility for decisionmakers. One way to refine the conceptis to define normal weatherevents as thoseevents that occurwithin a certainrange within a distribution, suchas, for instance,all eventsthat fall within one standarddeviation of the mean. In practice,historical records of various lengthsand reliabilities have been collected around the world for temperature,precipitation, storm events,and others. When data is available,such a statisticaldefinition lends itself to equating normal weatherwith "expected" weather,where expectationsare set accordingto the amount of the distribution defined as normal. For example,about 68% of all eventsfall within one standarddeviation of the mean of a bell-shapeddistribution. A changein the statisticaldistribution of a weathervariable-such as that asso- ciated with a change in climate-is troubling becausedecision makers may no longer expectthat the future will resemblethe past. For the insuranceindustry, as well as other decisionmakers who rely on actuarialinformation, such a possibility of a changingclimate is particularlytroubling. A climate changeis thus a variation or changein the shapeor location(e.g., mean)of a distributionof discreteevents (Katz, 1993). "Extreme" weatherevents can simply be definedas those not normal, however normal is chosento be defined.For instance,if normalweather events are thosethat occur within 2 standarddeviations of the mean,then about5% of all eventswill be classifiedas extreme. While it is possibleto classifyhurricanes as either"normal" or "extreme" in this manner,the simple factis that for mostcommunities any landfalling hurricane would qualify as an extremeevent because of their rarity at particular locationsalong the coast. From the standpointof thosehuman activities sensitive to hurricaneimpacts, it is often the casethat decisionsare madeand decisionprocesses established based on some set of expectationsabout what future weatheror climate will be like. Building codes,land-use regulations, insurance rates, disaster contingency funds are eachan example of decisionsthat are dependentupon an expectationof the frequencyand magnitudeof future normal and extremeevents. In short,decision makers typically establishpolicies based upon an expectationof normal weather.Yet for most coastalcommunities normal weatherhas historically 2 HURRICANES DEFINED 791 (or at least over the time of a human memory)meant no hurricanes!Consequently, people are often surprised when a hurricane does strike and then overwhelms responsecapabilities. Because decision makers do not alwaysconsider the possibility of extremeweather, when suchevents occur, they often revealsociety's vulnerabilities and sometimeslead to human disaster.A fundamentalchallenge facing societyis to incorporateinformation about weatherand climate risks into decision making in orderto take advantageof normalweather and to preparefor the extreme. The degreeto which societyexploits normal weatherand reducesits vulnerabilities to extremeweather is a function of how societyorganizes itself in the face of what is known about various typical and extreme weatherevents. The challengeis made more difficult by variability at all measurabletime scalesin the underlyingclimate, and hencein the frequency,magnitude, and locationof various weatherevents. And, of course,decisions that have a weatheror climate componentalso are ladenwith all of the political, practical,and social factorsthat influencepolicy. 2 HURRICANES DEFINED One of the most powerful naturalphenomena on the face of Earth,the hurricaneis a memberof a broaderclass of phenomenacalled cyclones.. The term cyclonerefers to any weathersystem that circulatesin a counterclockwisedirection in the Northern Hemisphereand in a clockwise direction in the SouthernHemisphere. "Tropical cyclones" typically form overocean waters of the tropics.The tropics arethe areaon Earth'ssurface between the Tropic of Capricornand the Tropic of Cancer,230 27" southand north of the equator,respectively. Extratropical cyclones, for comparison, form as a result of the temperaturecontrast between the colder air at higherlatitudes and warmerair closerto the equator.Extratropical storms form over both the ocean and land. Tropical cycloneshave been given differentnames depending on their region of origin. In the westernnorth Pacific, they are called typhoons,while in the Bay of Bengal they are referredto as severecyclonic storms of hurricaneintensity. In the Atlantic, Gulf of Mexico, Caribbean,and Pacific north of the equatorand eastof the internationaldateline they are hurricanes.Evidence of tropical cycloneshas been documentedin a variety of other geographiclocations including Europeand North Africa at earliergeologic times (Ager, 1993).Figure I showsthe tracksof all tropical cycloneswith winds greaterthan 39 mph for the IO-yearperiod 1979to 1988. The meteorologicalcommunity uses a number of terms to classify the various stagesin the life cycle of tropical cyclones.The following are definitions of tropical cyclonesused in the Atlantic Ocean basin(Pielke and Pielke, 1997): *This chapterconsiders hurricanes as an extrememeteorological event. It first discussesthe physical aspectsof hurricanes,including their developmentand impacts on ocean and land. It then overviews societalimpacts. 792 ~ 3 HURRICANES IN NORTH AMERICAN HISTORY 793 Tropical low A surfacelow-pressure system in the tropical latitudes. Tropical disturbance A tropical low and an associatedcluster of thunderstorms that has, at most, only a weak surfacewind circulation. Tropical depression A tropical low with a wind circulationof sustainedI-min surfacewinds of less than 34 knots (kt) [39 miles per hour (mph), 18 meters per second [mjs] circulating around the center of the low]. [A knot (i.e., a nautical mile per hour) equalsabout 1.15mph. A nauticalmile is the length of 1 min of arc of latitude.] Tropical storm A tropical cyclone with maximum sustained surface winds of 34 to less than 64kt (39 to 74mph, 18 to 33 mjs). Hurricane A tropical cyclone with maximum sustained surface winds of 64 kt (74mph, 33 mjs) or greater.(In the Pacific Oceanwest of the internationaldate line, hurricanesare called typhoons.They are the samephenomenon.) 3 HURRICANES IN NORTH AMERICAN HISTORY The word hurricane derives from the Spanish huracan,itself derived from the dialects of indigenous peoples of the Caribbeanand Latin America (Dunn and Miller, 1964). 'Hunraken' was the name of the Mayan storm god, and 'Huraken' was the god of thunderand lightning for the Quiche of southernGuatemala (Henry et al., 1994).The Tainosand Caribetribes of the Caribbeancalled their God of Evil by the name Huracan. Other indigenousdialects included words such as aracan, urican, and hurivanvucanto refer to "Big

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