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DISTRIBUTIONS OF LIGHTNING-CAUSED CASUALTIES AND DAMAGES SINCE 1959 IN THE UNITED STATES

 
Ronald L. Holle (formerly National Severe Storms Laboratory, NOAA,
Raúl E. López, retired from National Severe Storms Laboratory, NOAA
E. Brian Curran, National Weather Service, NOAA, Fort Worth, Texas
11th Conference on Applied Climatology, American Meteorological Society
January 1999
 
1. INTRODUCTION
 
This paper summarizes casualties and damages due to lightning in the U.S. based on the NOAA publication Storm Data. Curran et al. (1997) includes expanded versions of many of the figures and tables.
 
Annual summaries of weather impacts based on Storm Data have been published since 1990 by NOAA's National Weather Service. Table 1 shows the number of deaths, injuries, and costs of property damage from four types of convective weather during three recent typical years. Lightning caused 44% of the fatalities, 19% of the injuries, and 3% of the damages for all convective-weather reports, according to Storm Data. Absolute values of these numbers must be considered with caution, however, for reasons given in the next section.  When all types of weather-related casualties are examined, Table 2 shows that lightning stays near the top of the list; only flash and river floods rank higher than lightning in terms of deaths.
 
Knowledge of medical issues concerning lightning victims has grown greatly during the 1990s (Andrews et al. 1992; Andrews 1995; Cherington 1995; Cooper 1995; Cooper and Andrews 1995; Primeau et al. 1995; Cherington et al. 1997). This improved understanding of the medical profiles and demographic distribution of lightning victims has resulted in a multidisciplinary effort concentrating on lightning safety and education (Vavrek et al. 1999). A significant emphasis is being placed on sports and recreation (Bennett 1997; Walsh et al. 1997).
 
2. LIGHTNING CASUALTY AND DAMAGE REPORTS
 
Reports of damaging weather phenomena are compiled monthly at each National Weather Service office. The reports are sent to NOAA's National Climatic Data Center (NCDC) in Asheville, N.C. where Storm Data is assembled. This publication has been compiled with substantially the same procedures since 1959. For this paper, an electronic version of Storm Data was obtained from NCDC of only lightning reports. From 1959 to 1994, Storm Data had 3,239 deaths, 9,818 injuries, and 19,814 property-damage reports due to lightning. Each report contains:
 
- Year, month, day.
- Time in Local Standard Time (LST).
- State and county.
- Number, gender, and location of fatalities.
- Number, gender, and location of injuries.
-         Amount of damage.
 
Lightning-caused casualties and damages are often less spectacular and more widely dispersed in time and space than other phenomena such as tornadoes and hurricanes. Therefore, lightning deaths, injuries, and damages are underreported as follows:
 
* 33% more lightning deaths in Texas than Storm Data (Mogil et al. 1977).
* 28% more fatalities and 42% more injuries requiring hospitalization in Colorado     than Storm Data (López et al. 1993).
* The number of Storm Data events was under-reported by 367:1 in a review of insured personal property in 3 western states (Holle et al. 1996).
 
The latter paper leads to the conclusion that lightning-caused damages are actually similar to, or exceed costs of other phenomena in Table 1. When other unquantified losses are considered, lightning may be as large a cause of damages, and have as little change from year to year, as any weather type.

 

TABLE 1. Annual averages of casualties and property damage due to convective weather (thunderstorms) during 1992-1994 (from National Weather Service, Office of Meteorology). Order is by number of deaths per year.
Convective
weather type
Fatalities Injuries Damage ($millions)
Lightning 51 345 32
Tornadoes 47 1114 551
Thunderstorm wind 18 352 192
Hail 0 21 345

 

Factors contributing to underreporting include:

-Most casualty events involve one person.
-The National Weather Service relies on newspaper clipping services for many lightning events in Storm Data (López et al. 1993).
-Lightning is sometimes listed as a secondary rather than primary cause of a casualty by the medical system (Mogil et al. 1977; López and Holle 1998).

Nevertheless, Storm Data is the only consistent data source for several decades. In this report, its information was used without modification.

TABLE 2. Summary of 1994 weather casualties, and 30-year normals (from National Weather Service, Office of Meteorology). Order is by 30-year death rate, then by 1994 deaths.
Weather 1994 deaths 1994 injuries Deaths per year
Flash flood 59 33 139
River flood 32 14
Lightning 69 484 87
Tornado 69 1067 82
Hurricane 9 45 27
Extreme temperatures 81 298  
Winter weather 31 2690  
Thunderstorm wind 17 315  
Other high wind 12 61  
Fog 3 99  
Other 6 59  
Total 388 5165  

 

3. VARIATIONS BY STATE IN REPORTED NUMBERS

 
Section 3 shows the number of lightning reports by state, and the rank of each state, then Section 4 shows rates per population.
 
a.        Casualties
 
Figure 1 shows the rank of each state in lightning-caused casualties (both deaths and injuries). Florida has twice the number of casualties of any other state. The rest of the top ten states, in order, are Michigan, Pennsylvania, North Carolina, New York, Ohio, Texas, Tennessee, Georgia, and Colorado. Other high-ranking states are in southern and eastern regions of the country, and very populous states in the northeast. Fewest casualties are in Alaska (none), Hawaii, the District of Columbia, northwest states, Puerto Rico, and small eastern states.
 
b.      Fatalities
 
Florida has more than twice the number of lightning deaths of any other state (Curran et al. 1997). The other top-ten states are the same as for casualties except Louisiana, Maryland, and Arkansas replace Michigan, Georgia, and Colorado. Other state rankings usually do not change by more than 5 from casualties except:
 
* Michigan was in the top 10 casualty list, but not fatalities, because of two large injury cases (Ferrett and Ojala 1992).
* Lightning caused an aircraft crash that killed 81 people in Maryland in 1963;
that state became seventh in fatalities over the period.
 
Previous studies of lightning fatalities include Duclos and Sanderson (1990), who used data from the National Center for Health Statistics. Deaths from Storm Data have been plotted by state (Mogil et al. 1977) or at specific locations (Zegel 1967). Results were substantially similar to Figure 2.  Single-state maps by county have been compiled for Florida (Duclos et al. 1990), North Carolina (Langley et al. 1991), Michigan (Ferrett and Ojala 1992), and Colorado (López et al. 1995). A table of fatalities by Canadian province was developed by Hornstein (1962). Pakiam et al. (1981) plotted fatalities on a
map of Singapore. Maps of deaths divided by political boundaries were shown by Coates et al. (1993) for Australia and by Gourbičre et al. (1997) for France.
 

    c. Injuries

 
The distribution of injuries by state is nearly identical to casualties in Figure 1, since 75% of the casualties are injuries (Curran et al. 1997). Florida had nearly twice as many injuries as Michigan.

d. Damage Reports

 
The distribution of damage reports by state (Figure 2) has a high concentration over the plains from South Dakota to Texas. The largest number of damage reports is from Pennsylvania, where less than half as many casualties were reported as in Florida. Florida is first on all casualty lists but is not high on the damage list. Six of the 10 states with the
highest damage counts are on the first-ten lists for casualties, deaths, or injuries. But Kansas, Oklahoma, and Nebraska on the plains, and South Carolina do not have as high a casualty rank.
 
4. VARIATIONS BY STATE WEIGHTED BY POPULATION
 
a. Casualty Rate per Population
 
When population is taken into account, the maxima shift from populous eastern states to Rocky Mountain and plains states (Figure 3). The top two rates are from Wyoming and New Mexico; these states were 35th and 21st in number of casualties. Wyoming had most of its casualties in the 1960s and 1970s, and almost none since then. Southeast states often have high rankings in both Figures 1 and 3. The only states in the first 10 of both casualties and casualty rate are Florida, Colorado, and North Carolina.
 
b. Death Rate per Population
 
The map of lightning-caused death rate is similar to Figure 3 (Curran et al. 1997). New Mexico and Wyoming exchange first and second places in the lightning-caused death rates compared to the casualty list.
 
c.       Injury Rate per Population
 
Locations with high injury rates are in similar locations to those with high casualty rates (Curran et al. 1997). Florida and North Carolina are the only states that rank in the top ten of both injuries and injury rate. Otherwise, states with high injury rates are less populous than many or most other states. Lowest injury rates are from similar locations as casualty rates--Alaska, Hawaii, west-coast states, and smaller east-coast
states.
 
d.      Damage Report Rate per Population
 
A swath of high rates of damage reports is located from Idaho to the Dakotas, Oklahoma, and Arkansas (Figure 4). The plains also had high numbers of damage reports (Figure 2) with two exceptions. North Dakota did not have many actual reports, but this less populous state becomes sixth in damage rate. Texas had numerous reports, but its damage rate became small due to it being so populous. Holle et al. (1996) showed that Storm Data damage reports were underreported by 367:1 based on insurance claims. For
this reason, a reliable national representation of lightning damages may not be attainable from Storm Data alone.
 
5. YEAR-TO-YEAR VARIATIONS
 
The number of lightning deaths slowly decreased from 1959 to 1994, while injuries increased in the 50 states, District of Columbia, and Puerto Rico (Figure 5A). As a result, the ratio of injuries to deaths steadily increased through these years (Figure 5B).
 
While not shown here, after population growth was taken into account (normalization), several major trends were identified by López and Holle (1996, 1998). A 30% decrease in normalized casualties was attributed to improved forecasts and warnings, better awareness of the lightning threat, more substantial buildings available for safe refuge, and/or other socioeconomic changes. An additional 40% reduction in normalized deaths may be due to improved medical care and emergency communications. The injury rate decreased only 8% because of the transfer of some potential deaths into injuries; this transfer may be due to better emergency communications, medical attention, and other factors. Additional fluctuations on the scale of one or two decades broadly parallel national-scale changes in frequencies of thunder-days, cyclones, and surface temperature.
 
A gradual increase in damage reports (Figure 5C) could be due to population growth. Additional details of decadal changes by region and state in casualties and damages are in Curran et al. (1997).
 
Notable decreases in deaths were documented with long-term datasets in England and Wales (Elsom 1993), England and Wales compared to Australia (Golde and Lee 1976), and Singapore (Pakiam et al. 1981). Australian deaths increased from 1825 to 1918, then decreased to 1991 (Coates et al. 1993).
 
6. MONTHLY AND SEASONAL VARIATIONS
 
Lightning casualties and damages peak during July (Figure 6). Monthly percentages increase gradually before, then decline more quickly after July. Cloud-to-ground flashes also show these features (Orville and Silver 1997).
 
Casualties reach a higher July maximum than damage reports (Figure 6B).  The difference may result from a more focused exposure of people to lightning during summer months than spring or fall.
 
Prior Storm Data studies also found a July maximum, a slower increase before and a faster decrease after July (Zegel 1967; Mogil et al. 1977; Duclos and Sanderson 1990; López and Holle 1995; Ferrett and Ojala 1992; López et al. 1995). August maxima were found in Florida by Duclos et al. (1990), and Holle et al. (1993). In Colorado, Utah, and Wyoming, slightly more insurance claims were made in August than July (Holle et al. 1996). 
 
Seasonal and regional maps in Curran et al. (1997) show that summer casualties and damage reports closely follow annual maps. During other seasons, lightning cases are more frequent in southern states. Frequencies in the northeast are low except during the summer, while they are high on the West Coast during autumn and winter.
 
The largest number of Australian fatalities are in January; this is due to the reversal of seasons from the U.S. (Coates et al. 1993). Singapore fatality maxima in  November and April (Pakiam et al. 1981) are similar to the annual cycle of local thunderstorms.
 
7. TIME OF DAY VARIATIONS
 
Most lightning casualty and damage reports occur in the afternoon in the U.S. (Figure 7). Two-thirds of the casualties occur between 1200 and 1800 Local Standard Time (LST). They show a steady increase toward a maximum at 1600 LST, followed by a slightly slower decrease after the maximum. Damage reports are more broadly distributed in time (Figure 7B).
 
During the afternoon, there are up to 6% more casualties than damage reports, while some nighttime hours have 3% fewer casualties than damage reports. People are less likely to be involved in lightning-sensitive activities at night than during the day, and avoid activities during a brightly-illuminated storm.
 
Maximum numbers of lightning impacts from 1400 to 1600 LST were documented by Duclos et al. (1990), Ferrett and Ojala (1992), and López and Holle (1995). Duclos and Sanderson (1990) found an 1800 LST peak in North Carolina deaths.
 
Highest frequencies of casualties in all U.S. regions are typically within one hour of 1500 LST (Curran et al. 1997), while damage reports usually peak an hour or two later. Narrower distributions are apparent in the Rockies, southeast, and northeast. The broad time series in the plains and midwest, especially for damage reports, may be due to nocturnal thunderstorm complexes such as MCSs.
 
The daily 6-hour sequence shown in Curran et al. (1997) is as follows:
 
+ At night (0000-0559 LST), casualties and damage reports are most frequent in the plains, upper midwest, and a few populous eastern states. Compared to Figures 1 and 3, there is a shift in highest-ranking states to the north and east. Of the 29 deaths from 0000-0559 LST, 59% occurred when people were in a house set on fire by lightning. The other common situation was when people were camping in tents (21%).
+ Casualties in the morning are spread widely across the country. Damage reports are most common on the plains.
+ Casualties during the afternoon resemble Figure 1, since these are the most frequent hours for deaths (67%) and injuries (63%). Damage reports are not as closely related to the 24-hour map in Figure 2, since afternoon damage reports are only 41% of the Storm Data reports.
+ Evening deaths and injuries are distributed similarly to nighttime. The distribution of evening damage reports was similar to Figure 2.
 
Seasonal variations are as follows (Curran et al. 1997):
 
o Winter: Casualties in winter are erratic, and damage reports are spread through the 24 hours.
o Spring: Casualties occur during nearly the same afternoon hours as for the entire year and country. There is a secondary peak before noon. Damage reports in spring show a weaker diurnal cycle than spring or yearly damages.
o Summer: Casualties and damage reports follow annual curves.
o Autumn: Casualties have a broad afternoon peak and a secondary morning peak. Damage reports are spread through the day in a manner similar to spring, but are most common in late afternoon.
 
8. OTHER INFORMATION IN STORM DATA
 
a. Gender
 
Males account for 84% of the lightning fatalities, 82% of injuries, and 83% of casualties (Curran et al. 1997). Corresponding ratios indicate males being killed 4.6 times as often as females, and injured 5.3 times more often as females.
 
Similar ratios were found in the U.S. (Duclos and Sanderson 1990; Duclos et al. 1990; Langley et al. 1991; Holle et al. 1993), Singapore (Pakiam et al. 1981), and England and Wales (Elsom 1993). Other studies have shown males in their twenties to be the most frequent victims of lightning. The digital Storm Data record does not include age, although the descriptive paragraph in the printed publication usually does provide the age.
 
b. Location
 
Location categories in Storm Data are not very useful. "Not reported" and "at various other and unknown locations" account for 40% of the entries. In addition, categories are often not well defined. More can be learned about victims' situations from other datasets or the descriptive paragraphs in Storm Data. This time-consuming task has not been performed for the entire country, but results from some states are:
 
* Lightning victims in North Carolina were most often at and near their home (Duclos and Sanderson 1990). In contrast, Langley et al. (1991) found that North Carolina deaths were most often in a farm, field, or garden.
* A significant number of lightning victims were in the vicinity of water in
Florida (Duclos et al. 1990; Holle et al. 1993).
* Lightning casualties during recreation have increased since 1950 in Colorado, while agricultural casualties decreased (López et al. 1995).
* Similar results were found in Singapore (Pakiam et al. 1981) and Australia
(Coates et al. 1993).
 
It is also important to go beyond the Storm Data digital record to find a person's activity, which can tell about a lightning victim's situation. Many of the above papers include or link the victim's activity to location.
 
c. Victims per event
 
The most common situation is for only one victim to occur in a lightning incident. For death incidents only, 91% had one fatality; another 8% had two people killed in an incident. The largest fatality event was the Maryland airliner crash in 1963 that killed 81 people. For injuries only, 68% had one injury. The largest injury event was 90 at a Michigan campground (Ferrett and Ojala 1992). The distribution of casualty events closely resembles the injury distribution. The same tendency for single victims was noted in the U.S. (Zegel 1967, López et al. 1995), Singapore (Pakiam et al. 1981), and Australia (Coates et al. 1993).
 
c. Day of week
 
Sunday has 24% more deaths than other days; a slight tendency for more deaths is also evident on Wednesday (Curran et al. 1997). The most injuries are on Wednesday and weekend days, and the least on Tuesday and Friday. Casualties are most frequent on Sunday, next is Saturday, then Wednesday, as for injuries. Damage reports are greatest on Monday, then decrease on most other days until reaching the lowest number on Saturday. The existence of more casualties on the weekend suggests that recreation is
a factor on those days. It is difficult to understand why there are more damage reports on weekdays, but this trend could result from reports in newspapers that do not publish every day.
 
d. Damage report costs
 
According to Storm Data, nearly half of all lightning damages are between $5,000 and $50,000 (Curran et al. 1997). The categories of $500-5,000 and $50,000-$500,000 are also frequent; these three categories account for 93% of Storm Data reports.
 
Storm Data amounts are much larger than insured losses paid for claims by homeowners and small businesses in Colorado, Utah, and Wyoming (Holle et al. 1996). Over a third of the insurance losses were between $251 and $1,000, and only a few were over $5,000. It is recognized, however, that it is not possible for National Weather Service staff preparing Storm Data to be aware of small losses that do not result in an emergency call and are not in newspapers.
 
9. SUMMARY AND CONCLUSIONS
 
Florida led the nation in actual deaths and injuries. The largest number of damage reports came from Pennsylvania. There were large variations among decades in both casualties and damages.
 
When population was taken into account, Wyoming and New Mexico led the nation in death, injury, and casualty rates. The highest rate of damage reports was on the plains from North Dakota to Oklahoma.  Population-weighted casualties and damages decreased until the 1990s, then increased.
 
July maxima existed for all lightning reports. Casualties had a strong July maximum, while damage reports were spread more evenly through the year. Casualties and damages in northern states had narrower distributions centered on summer than those in states to the south.
 
Two-thirds of the casualties occurred between 1200 and 1600 LST.  Casualties increased steadily to a maximum at 1600 LST, followed by a somewhat faster decrease. Damage reports lagged casualties by two to three hours. There were relatively frequent damage reports at night in plains and midwest states.
 
For incidents involving deaths (injuries) only, 91% (68%) of the cases had one fatality (injury). The dominance of single-person events shows the need for lightning safety education so that people take personal responsibility for their own threat from lightning.
 
Half of all lightning-caused damages were between $5,000 and $50,000 according to Storm Data, but comparison with other datasets shows these entries to include more widely known events and fewer small losses. Together with an unusual day-of-week pattern of damages, it appears that damage reports are poorly represented in this dataset.
 
Comparisons of casualty and damage results should be made with ground-strike data on annual, diurnal, monthly, and seasonal scales. A study is underway by the authors to identify trends in the activities of casualties over a century.
 

 

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