Distributions and Trends of Death and Destruction from Hurricanes in the United States, 1900–2008 H. E. Willoughby1 Abstract: Because annual death and destruction from hurricanes in the United States can vary by > 4 orders of magnitude, common log- arithms are convenient measures. If the data are stratified into years when at least one major hurricane (maximum winds > 49 m=s) made landfall and those without a major-hurricane-landfall, logarithmic mortality and damage in both subsets appear to be normally distributed. Combined log-normal distributions accurately represent the data. From 1900 through 2008, total hurricane mortality decreased with a halving time of 26 years. Consistent with previous analyses, historical damage normalized for population growth, increasing individual wealth, and inflation did not exhibit significant trends in either subset. Comparison between the complete 1900–2008 record and a truncated version spanning 1900–2000 shows that the effects of hurricanes since 2000, especially Katrina, doubled the expected loss of life and increased the expected damage by 10%, consistent with the relatively large statistical uncertainty in estimation of the model parameters. In the context of the model, the expected frequency of disasters that cause > $100 billion in damage is approximately three times a century and for those that claim > 1;000 lives is approximately once a century. DOI: 10.1061/(ASCE)NH.1527-6996.0000046. © 2012 American Society of Civil Engineers. CE Database subject headings: Hurricanes; Damage; Fatalities; Statistics; United States; History. Author keywords: Hurricane; Damage; Mortality; Climate; Statistics. Introduction hurricane landfalls with a Poisson distribution, and the normalized damage for each occurrence with a log-normal-distribution. In this Since 1900, tropical cyclones (TCs) making landfall in the United formulation, only 15% of the variance arose from random landfall States ended 18,000 lives prematurely and destroyed US$400 occurrence, whereas most of the variance stemmed from differen- billion in property, corrected for inflation to 2005 (Blake et al. ces in effects of individual landfalls. Damage during most seasons 2007; Pielke et al. 2008). Normalization of historical damage for was dominated by single events. Exceptions to this generalization increasing population and individual wealth, and for inflation include 1915, 1954–1955, and 2004–2005. (Pielke and Landsea 1998; Pielke et al. 2008), shows that historical This paper analyzes annually aggregated damage and mortality. > $ ; storms would have inflicted US 1 200 billion in damage from This approach is appropriate because governments and corpora- 1900 through 2008 with constant early 21st century coastal devel- tions have annual budget cycles. Primary insurers set rates and opment. Thus, the cost of hurricane damage is a significant eco- negotiate reinsurance contracts every year. Moreover, potential nomic misfortune. Indeed, Galbraith (1954) traces the roots of the climate signals will appear as year-to-year variations of effects. Great Depression, in part, to collapse of the southeast Florida real Alternative analyses that treat individual landfalls can be used to estate bubble and subsequent loss of bank deposits and liquidity validate catastrophe models (Pielke et al. 1999) and to provide vital after the 1926 Miami Hurricane. Conversion of the deaths to a input for social-science research, but definition of systematic cli- dollar figure by using late 20th century “Statistical Value of Life” mate changes and measurement of effects on the economy as a (US$5 million; Fisher et al. 1989) yields a total US$90 billion in economic effect for 1900–2008 hurricane mortality. whole require annually aggregated statistics. Quantitative assessments of TC effects are essential to rational The HURDAT climatology (Jarvinen et al. 1984) shows that policy and planning. The insurance industry, for example, estimates from 1900 through 2008, 182 hurricanes crossed the U.S. coastline. windstorm risk with Monte Carlo, “catastrophe models” that con- Of these, 71 were major hurricanes in Saffir-Simpson categories > = volute winds from climatologically realistic virtual hurricanes with 3, 4, and 5, with maximum wind (V max) 49 m s (111 miles > % the spatial distributions of insured properties (Vickery et al. 2000; per hour). Major hurricanes account for 80 of U.S. tropical- Grossi and Kunrather 2005). By using a less elaborate approach, cyclone property damage (Pielke and Landsea 1998). Landfall Katz (2002) modeled annual hurricane damage by using a com- incidence varied on a multidecadal time scale. Early in the 20th pound statistical distribution. He represented the frequency of century, hurricane landfalls were more frequent than the long-term average. Then through the mid-1920s, landfalls occurred at a some- 1Distinguished Professor, Dept. of Earth and Environment, what below average rate. A prolonged period of above-average Florida International Univ., MMC/PC 344, Miami, FL 33199. E-mail: landfalls began in approximately 1926 and continued through [email protected] 1970. From 1971 through 2003, landfalls averaged slightly more Note. This manuscript was submitted on December 17, 2009; approved than one per year; although this respite was interrupted in 1985 on January 11, 2011; published online on January 17, 2012. Discussion when six landfalls occurred, tying the record set in 1916. The num- period open until July 1, 2012; separate discussions must be submitted for individual papers. This paper is part of the Natural Hazards Review, ber of observed Atlantic TCs increased dramatically after 1995, but Vol. 13, No. 1, February 1, 2012. ©ASCE, ISSN 1527-6988/2012/1-57– the increase did not reach U.S. shores until 2004 and 2005, when a 64/$25.00. total of nine landfalls occurred. NATURAL HAZARDS REVIEW © ASCE / FEBRUARY 2012 / 57 Downloaded 05 Mar 2012 to 131.94.186.10. Redistribution subject to ASCE license or copyright. Visit http://www.ascelibrary.org Multidecadal variations in hurricane activity throughout the Atlantic basin may be influenced by the Atlantic multidecadal oscillation (AMO), a 50–70 year episodic change in the Atlantic oceanic thermohaline circulation (Goldenberg et al. 2001; Kerr 2005). The AMO is hypothesized to modulate the inhibiting effect of vertical wind shear in the eastern tropical Atlantic. Apparent century-scale increases in Atlantic-basin-wide intensities and numbers have been attributed to anthropogenic global warming (Emanuel 2005; Webster et al. 2005). Although these increases seem qualitatively consistent with the model of hurricanes as classical heat engines running between the warm sea surface and cold upper troposphere (Emanuel 1991), they also may be attrib- utable to better detection (Landsea et al. 2010). Downscaled global climate model results show that the increase in intensity of the strongest TCs should be evident above random variation only after the late 21st century (Bender et al. 2010). Even as the intensities of – > = hurricanes in Saffir-Simpson categories 3 5(V max 49 m s) become stronger and more common, the number of hurricanes in general will probably decrease. An emerging international con- sensus based upon this view (Knutson et al. 2010) promises to – reconcile the competing explanations for the apparent increase Fig. 1. U.S. annual deaths attributable to hurricanes, 1900 2008 (data from Blake et al. 2007); the solid curve is a fitted exponential in Atlantic-basin hurricanes since 1970 (Vecchi et al. 2008). trend that approximates the time-varying arithmetic mean Apart from multidecadal variation that seems weakly correlated with basinwide activity, the numbers of U.S. landfalls do not show statistically significant trends over the 109-year record (Landsea 2005, 2007; Holland 2007; Wang and Lee 2008), and year-to-year nonzero mortality. The logarithmic fits track time-varying geomet- serial correlation is not strong. ric means, which are usually smaller than the arithmetic means and Landfall occurrences stratified by nonmajor and major hurri- do not have the mean-value property. That is, the area under the canes are reasonably well modeled by using Poisson distributions logarithmically fitted curve is not the total of the quantity being with means of 1.02 and 0.65 (Elsner et al. 2001; Katz 2002). The described. Nevertheless, because of the large range of values, log- combined landfall total is described by a Poisson distribution with a arithmic transformations simplify the analysis. The halving time of mean of 1.67. The corresponding variances are 0.93, 0.65, and the exponential nonlinearly fitted to nonlogarithmic hurricane mor- 1.67. Chi-square tests of yearly landfall counts against Poisson dis- tality is 25.8 years. It decreases from 478 deaths annually in 1900 to tributions with these means yield p-values of 0.4 to 0.9, so that 26 in 2008. This decrease in mortality as a result of better forecasts there is no reason to reject Poisson models. and warnings (Sheets 1990) is a significant achievement in the face In this paper, statistical trends and probability density functions of a growing population at risk. (PDFs) are derived for hurricanes’ human and economic effects. Inflation-adjusted hurricane damage (not shown) has a range Key limitations are that the time series are imperfectly measured, even greater than for deaths, 4 orders of magnitude, from US nonstationary, and probably too short to resolve long-term varia- $12 million dollars in 1962 and 1987 (excluding years