a. Casualties

Figure 1 uses shading to separate the top 30 states in lightning-caused casualties (Fig. 1a) and damages (Fig. 1b) by steps of 10 in rank. Florida has more than twice as many casualties as any other state (Table 3). In order, the other top 10 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 the populous northeastern states. Relatively frequent casualties are apparent in Colorado, New Mexico, and Arizona. The only similar maps that were previously published showed deaths, injuries, and damages by county in Michigan (Ferrett and Ojala 1992) and casualties by county in Colorado (López et al. 1995).

There was an average of 363 casualties per year (Table 3) from 1959 to 1994. The National Lightning Detection Network (Cummins et al. 1998) identified an average of 21 746 000 cloud-to-ground flashes per year from 1992 to 1995 (Orville and Silver 1997). Assuming this 4;chyr average to be representative, the result is one casualty for every 60 000 flashes. Since approximately 70% of the flashes were detected, about 86 000 flashes occurred for each casualty.

b. Fatalities

Fatalities are distributed similarly to casualties (Curran et al. 1997). Florida had more than twice as many lightning deaths as any other state. The other top 10 states are the same as for casualties except Louisiana, Maryland, and Arkansas replace Michigan, Georgia, and Colorado (Table 3). Lightning caused an aircraft crash that killed 81 people in Maryland in 1963; that state became seventh in fatalities over the period. Michigan was in the top 10 casualty list, but not that of fatalities, because of two injury cases: 90 people were injured at a campground in one case and 45 at a National Guard camp in another (Ferrett and Ojala 1992).

Previous studies of lightning impacts on people often described fatalities. Thresholds of the number of deaths rather than state ranks were shown by Duclos and Sanderson (1990) using data from the National Center for Health Statistics from 1968 to 1985. Deaths from Storm Data were plotted by state (Mogil et al. 1977) from 1968 to 1976 or at specific locations (Zegel 967) from 1959 to 1965; results were similar to Fig. 2. Single-state maps of deaths 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). Outside the United States, a table of fatalities by Canadian province from 1939 to 1958 was developed by Hornstein (1962). Pakiam et al. (1981) plotted each fatality on a map of Singapore. Maps of lightning deaths divided by political boundaries were shown by Coates et al. (1993) for Australia and Gourbière et al. (1997) for France.

c. Injuries

The distribution of injuries by state is not shown here but is in Curran et al. (1997). The distribution is nearly identical to casualties in Fig. 1a, since 75% of the casualties are injuries. Florida had nearly twice as many injuries as Michigan. Michigan was second in injuries but 12th in deaths due to large numbers of injuries in the two cases mentioned earlier. Georgia and Massachusetts on the injury list replace Arkansas and Maryland on the fatality list.

The U.S. average is 2.54 injuries per death. However, Missouri had only slightly more injuries (93) than deaths (78), while Puerto Rico had six injuries but 30 deaths; a few other locations approach a 1:1 ratio. The geographical distribution of the injury to death ratio has no coherent pattern (not shown). A low ratio may indicate an underreporting of injuries and that deaths are the better statistic for a state.

d. Damage reports

The distribution of damages by state (Fig. 1b) is very different from that of casualties. Damage reports are relatively frequent over the plains from South Dakota to Texas. The largest number is from Pennsylvania, where less than half as many casualties were reported as in Florida. While Florida is first on all casualty lists, it is not high on the damage list. Six of the 10 states with the highest damage counts are on the top 10 lists for casualties, deaths, or injuries. But Kansas, Oklahoma, Nebraska, and South Carolina do not have a high casualty rank. There are few damage reports in New Mexico, where there is a rather large number of deaths.

The damage to casualty report ratio tends to be near 1 or less in the southwestern and southeastern states, and Florida (not shown). Northwestern states have nearly two damage reports for every casualty. It is unknown whether this ratio is influenced by better reporting of casualties, a greater underreporting of damages in some states, or other factors.

e. Summary

Florida led the nation in casualties, deaths, and injuries by a wide margin. The largest number of damage reports came from Pennsylvania, but it had less than half as many casualties as Florida. North Carolina had uniformly high frequencies in all categories: second in deaths, fourth in injuries, and third in damages. Kansas ranks were less consistent; it was fourth in damages, but 25th in deaths and 22d in injuries. Alaska, Hawaii, Puerto Rico, the District of Columbia, and Nevada had very few casualties and damage reports over the 36-yr period.

a. Casualty rate per population

Figure 2a shows major differences between the rates of lightning-caused casualties and reported numbers in Fig. 1a. The main effect of taking population into account is to shift maxima from populous eastern states to the Rocky Mountain and plains states. The top two rates are from Wyoming and New Mexico (Table 4); these states were 35th and 21st in number of casualties (Table 3). Wyoming had most of its casualties in the 1960s and 1970s (section 4) and almost none since then. Southeastern states often have high rankings in both Figs. 1 and 2. The only states in the top 10 for both casualties and casualty rate are Florida, Colorado, and North Carolina. Similar maps to those of casualty rate per state population were in Ferrett and Ojala (1992) and López and Holle (1995). López et al. (1995) showed casualty rates for Colorado counties.

b. Death rate per population

The map of lightning-caused death rate for the United States (not shown) is very similar to the casualty map in Fig. 2a. New Mexico and Wyoming have the highest lightning-caused death rates, as for casualty rate, except they exchange first and second places. The national average is 0.42 deaths per million people per year. This rate is one-fourth the rate of 1.7 deaths per million in Singapore for 1961=n79 (Pakiam et al. 1981). In contrast, the U.S. rate is more than two orders of magnitude greater than the 0.001 rate in Australia from 1980 to 1989 (Coates et al. 1993). Similar maps of death rates per population were shown by Ferrett and Ojala (1992), Zegel (1967), and Duclos and Sanderson (1992).

c. Injury rate per population

Locations with highest injury rates are almost identical with high casualty rates (Curran et al. 1997). Florida and North Carolina are the only states that rank in the top 10 for both injuries and injury rate. Otherwise, states with high injury rates have smaller than average to average populations. The only previous injury rate map was by Ferrett and Ojala (1992) over a similar period.

d. Damage report rate per population

A swath of high rates of damage reports is located from Idaho into the Dakotas to Oklahoma and Arkansas (Fig. 2b). However, except for the plains maximum, there is not much of a pattern. The plains also had high numbers of damage reports with two exceptions. North Dakota did not have many reports, but this less populous state becomes sixth in damage rate. Although Texas had numerous reports, its damage rate was small due to it being so populous. Recall that Holle et al. (1996) showed Storm Data damage reports to be underreported by a ratio of 367:1 based on insurance claims, so a highly organized pattern for damages should not be expected. New Mexico had few damage reports (41st in country) but a high casualty rate (second). No previous publication has shown a damage rate map.

e. Summary

Wyoming and New Mexico led the nation in lightning-caused death, injury, and casualty rates. The highest rates of damage reports were from Idaho to the plains. New Mexico had a low damage rate while it was second in casualty rates. Alaska, Hawaii, California, Washington, Puerto Rico, and Oregon always had low rates of casualties, deaths, and injuries.

a. Nation by year

The number of lightning deaths decreased from 1959 to 1994, while injuries and casualties increased (Fig. 3a). The resulting ratio of injuries to deaths increased substantially over the period (Fig. 3b). 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 other socioeconomic changes.

• An additional 40% reduction in normalized deaths may be due to improved medical care, and emergency communications and transportation.

• Normalized injuries decreased only 8% due to the transfer of potential deaths into injuries.

• Additional fluctuations on the scale of one or two decades broadly parallel national-scale changes in frequencies of thunder days, cyclones, and surface temperature.

The number of damage reports (Fig. 3c) shows a gradual increase from 1959 to 1994 that could be due to population growth. While Holle et al. (1996) showed that Storm Data lightning damages are vastly under-reported, Fig. 3c appears to have no systematic bias through time.

Notable decreases in lightning deaths over long periods have been documented in England and Wales from 1852 to 1990 (Elsom 1993), in England and Wales compared to Australia from 1920 to 1969 (Golde and Lee 1976), and in Singapore from 1922 to 1979 (Pakiam et al. 1981). Coates et al. (1993) showed an increase in the number of lightning deaths in Australia from 1825 to a maximum in 1918, then a decrease through 1991.

b. Nation by decade

Yearly data in Fig. 3 are divided into decades in Fig. 4. Casualties are somewhat more frequent in the 1990s compared to earlier decades, and damages are much more frequent in the 1990s (Fig. 4a). Population-weighted casualties (Fig. 4b) show a decrease until the 1990s, as well as damages. Values for the 1990s were obtained by doubling 1990=n1994 values.

c. Region by decade

Decadal trends in the rates of casualties and damages are graphed for eight regions in Fig. 5. The casualty rate has increased during the last one or two decades in the West Coast, southern Rockies, southern plains, and southeast regions but stayed the same elsewhere. Damage report rates have increased during the last decade or two in all but the West Coast and Midwest regions. Time series for unweighted decadal data (Curran et al. 1997) are nearly identical to those in Fig. 5, since a region's population changes are less variable from decade to decade than the lightning reports.

d. States by decade

New Mexico and Arkansas are always among the top 10 states for casualty rate (Fig. 6, left column). Highest casualty rates are consistently in the Rocky Mountain and southeastern states; there is a shift toward the southwest with time. Most states stay within one group of 10 from the previous decade. Wyoming has a high rate in the 1960s but drops to a low rate by the 1990s.

Nebraska and Oklahoma are among the top 10 states for damage rates in every decade. Highest rates are in the northern plains, southeastern, and northeastern states. As noted earlier, damage reports are not especially reliable; for example, Georgia increased from 83 reports in the 1960s to 321 from 1990 to 1994, while Mississippi decreased from 58 to 6 over the same two periods.

a. Nation by month

Lightning casualties and damages peak during summer, and July has the maximum percentage frequencies for all categories (Fig. 7). Monthly percentages increase gradually before, then decline more quickly after, July. Cloud-to-ground flashes from 1992 to 1995 also show these features (Orville and Silver 1997). A higher percentage of deaths occurs in spring than injuries. The 1963 Maryland aircraft crash that killed 81 people accounts for the December anomaly.

Casualties reach a stronger July maximum than damage reports (Fig. 7b). Differing distributions may result from a greater exposure of people to lightning during summer than spring or fall. In contrast, immovable objects are shown to be impacted more often than people before and after the summer maximum; the shape of the damage report distribution may represent better the actual flash distribution.

Most prior Storm Data studies found a July maximum, a slower increase before and a faster decrease after July (Zegel 1967; Mogil et al. 1977; Duclos and Sanderson 1990; Ferrett and Ojala 1992; López and Holle 1995; López et al. 1995). In Florida, however, August maxima were found in fatalities (Duclos et al. 1990), and fatalities and property damages (Holle et al. 1993); injuries in the latter study peaked in July. Slightly more lightning insurance claims were made during August than July in Colorado, Utah, and Wyoming (Holle et al. 1996). Singapore at 1;dgN had fatality maxima in November and April in an annual cycle similar to that of local thunderstorms (Pakiam et al. 1981). In Australia, the largest number of fatalities were in midsummer (January), but the buildup to the maximum was somewhat faster than the dropoff (Coates et al. 1993).

b. Region by month

By region, Fig. 8 shows that damage reports are usually spread more widely through the year than casualties. Both casualties and damages tend to have narrower distributions to the north centered on summer than to the south. Broadest monthly distributions are in the southern plains. Northern areas have up to 4% more casualties and damages in midsummer, while southern regions have more cases in spring and, to a lesser extent, in autumn.

c. Nation by season

The spring map of 1840 casualties during March, April, and May (Fig. 9) is similar to the annual pattern (Fig. 1a), except northeastern states have less casualties in spring than other regions. The 3590 spring damage reports show a similar distribution to the year in Fig. 1b, except for the same reduction in the north-east. Summer maps of 9586 casualties and 13 369 damage reports are almost identical to the annual map, since summer has 73% of the year's casualties and 67% of the damages. The 1464 autumn casualties return to high rankings in the southern plains. West Coast states rank relatively high in casualties during autumn and winter, but very low over the entire year. The 2511 autumn damage reports are distributed similarly to the spring pattern. Only 167 casualties occurred in 21 states during winter; the highest concentration is in the southern plains. The West Coast region ranks relatively high in winter, as in autumn. Winter damage reports (344) are most common in the southern plains. California and Hawaii rank among the top 30 states in winter but rank low in summer.

In summary, summer maps of casualties and damage reports closely follow the annual maps. During other seasons, lightning cases are more frequent in the southern states. Frequencies in northeastern states are low except during summer and are relatively high in the West Coast region during autumn and winter.

a. Nation

Most lightning casualty and damage reports occur in the afternoon in the United States (Fig. 10a). Two-thirds of all casualties occur between 1200 and 1800 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 through the day; they have a steeper increase until the 1700 LST maximum, then a steady decrease until midnight. Storm Data has times associated with 66% of the casualties and 61% of the damage reports.

During the afternoon, there are up to 6% more casualties than damage reports, while some nighttime hours have nearly 4% more damage reports than casualties (Fig. 10b). People may be less likely to be involved in lightning-sensitive activities at night than during the day and tend to avoid activities during a brightly-illuminated nighttime storm. An additional reason for the difference is that damages may not be identified until people arrive home in late afternoon at the end of the work day. Nocturnal mesoscale convective systems (MCSs) over the plains in summer can produce over 3000 ground strikes an hour (Goodman and MacGorman 1986).

By region, highest frequencies of casualties are typically within one hour of 1500 LST (Curran et al. 1997). Damage reports usually peak an hour or two later than casualties. Relatively narrow distributions are apparent in the northern Rockies, the southeast, and the northeast.

Maximum lightning impacts from 1400 to 1600 LST were documented for Florida deaths (Duclos et al. 1990), Michigan deaths, injuries, and damage reports (Ferrett and Ojala 1992), and U.S. casualties (López and Holle 1995). Duclos and Sanderson (1990) found an 1800 LST peak in North Carolina deaths.

b. 6-h periods

During the night (0000-0559 LST), casualties and damage reports are most frequent in the plains, northern Mid-west, and a few populous eastern states (Fig. 11). Compared to Fig. 1a for the year, highest-ranking states shift to the north and east. Only the first 27 ranks of casualties are shown; states lower than 27th have one or zero casualties. There were 62 deaths (3% of fatalities with known times), 135 injuries (2%), and 1753 damage reports (15%) in Storm Data during these nighttime hours. Storm Data indicated that 59% of the deaths at night from 1980 to 1994 occurred when people were in a house set on fire by lightning, and 21% were campers in tents.

Casualties in the morning (0600=n1159 LST) are spread widely across the country (Fig. 11). Damage reports are most common on the plains in a pattern similar to nighttime. The morning had 11% of the deaths, 13% of the injuries, and 10% of the damage reports.

Casualties during the afternoon resemble the distribution in Fig. 1a for the entire day, since these are the most frequent hours for deaths (67%) and injuries (63%). But afternoon damage reports (41%) are not as closely related to the whole day map in Fig. 1b. Afternoon maxima were also found for deaths, injuries, and damage reports in central Florida (Holle et al. 1993), fatalities in Australia (Coates et al. 1993), and casualties and damage reports in Colorado (López et al. 1995).

Evening deaths (18%) and injuries (22%) are distributed similarly to nighttime. Evening damage reports are more similar to the whole-day map in Fig. 1a.

c. Seasons

Casualties in spring (Fig. 12) occur during nearly the same afternoon hours as for the entire year and country in Fig. 10, except for a secondary peak before noon. Spring damage reports show a weaker diurnal cycle than spring casualties, or damages for the year, and occur several hours later than casualties. Summer casualties and damage reports follow the annual curves, since they compose more than half of the year's sample. Autumn casualties occur in a broad afternoon maximum and have a secondary morning peak. Autumn damage reports are spread through the day in a manner similar to spring, are most common in late afternoon, and lag casualties by several hours. Winter casualties are distributed erratically, as shown by a maximum at 0900 LST and a secondary peak during midafternoon; the sample is only 63 cases. Winter damage reports are spread evenly across both day and night.

a. Gender

Males account for 84% of the lightning fatalities, 82% of injuries, and 83% of casualties for the country. By region, between 76% and 94% of the deaths and injuries are to males (Curran et al. 1997). Corresponding ratios indicate that males are killed 4.6 times as often as females and injured 5.3 times more often than females. Storm Data does not specify gender for 18% of the deaths and 34% of injuries, and has “both” for deaths when one male and one female were killed in the same event. A similar definition for both applies to injuries.

Males were found to be 79%=n89% of the victims in the United States (Duclos and Sanderson 1990), Florida (Duclos et al. 1990; Holle et al. 1993), North Carolina (Langley et al. 1991), Singapore (Pakiam et al. 1981), and England and Wales (Elsom 1993). Numerous studies have suggested that males in their twenties are the most frequent victims of lightning. The digital Storm Data record does not include age, although the descriptive paragraph often provides this information.

b. Location

Storm Data divides the locations of lightning victims into eight groups and two unknown categories (Fig. 13). Starting with the most frequent, the categories are as follows.

• “Not reported” and “at various other and unknown locations” account for 40% of Storm Data entries.

• “Open fields, ballparks, playgrounds, etc.” is the next largest category in every region, the United States, and Michigan (Ferrett and Ojala 1992).

• “Under trees” is the third largest group in the United States, most regions, and Michigan (Ferrett and Ojala 1992).

• “Water related, fishing, boating, swimming, etc.” is next in the United States and most regions.

• “Golfing” and “golfing under trees” account for 8% of known lightning casualties in the United States. While there is a widespread impression that golfers are the most frequent victims of lightning, this is not the case.

• “Driving tractors, farm equipment, heavy road equipment, etc.” is a small segment in Storm Data since 1959. But agricultural activities in rural areas were common situations for lightning victims earlier in the century (López et al. 1995).

• “Telephone-related” is an infrequent but persistent source of lightning casualties in all regions (Andrews et al. 1992).

• “Radios, transmitters, antennas, etc.” occur at a low rate in all regions.

These location categories are of limited value; more can be learned about locations from other datasets or the descriptive paragraphs in Storm Data. This time-consuming task has not been performed for the entire country. But North Carolina medical examiner data have been used to develop two systems of victim locations. Casualties in North Carolina were most often at their home or in the home's surroundings from 1972 to 1984 (Duclos and Sanderson 1990), while Langley et al. (1991) found that fatalities were most often in a farm, field, or garden. In Florida, a significant number of lightning victims were in the vicinity of water (Duclos et al. 1990; Holle et al. 1993). Colorado lightning casualties increased during outdoor recreation since 1950, while agricultural casualties decreased (López et al. 1995). Not only is location important, but a person's activity can tell a great deal about a lightning victim's situation.

c. Victims per event

The most common situation is for one victim to be involved in an incident when someone was killed or injured by lightning. Table 5 shows that for incidents with deaths only, 91% of the cases had one fatality and 8% had two people killed. The largest fatality event was the Maryland airliner crash that killed 81 people. For incidents with injuries only, 68% of the cases had one injury. The largest injury event involved 90 people at a campground in Michigan (Ferrett and Ojala 1992). The distribution of casualty events closely resembles the injury distribution.

The same tendency for single victims was noted in fatalities in the United States (70%) by Zegel (1967), Singapore (85%) by Pakiam et al. (1981), and Australia (92%) by Coates et al. 1993). In Colorado, one person was involved in 89% of the deaths, 70% of the injuries, and 66% of the casualties (López et al. 1995).

d. Day of week

Sunday has 24% more lightning deaths than other days; a tendency for more fatalities is evident on Wednesday (Curran et al. 1997). The largest numbers of injuries are on Wednesday and weekend days, and the fewest on Tuesday and Friday. The casualty distribution follows the injury curve. Damage reports are greatest on Monday, then decrease until reaching the lowest number on Saturday. The existence of more casualties on the weekend suggests that recreation is a factor. 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.

e. Damage report costs

According to Storm Data, nearly half of all lightning damages were between $5000 and $50 000 (Curran et al. 1997). The categories of $500–5000 and $50 000–$500 000 are also frequent; these three categories account for 93% of the reports. All regions of the United States have the interval of $5000–$50 000 as most frequent, and $500–$5000 is next. There is a tendency for somewhat higher costs from the southern plains east-ward, compared to the northern plains westward. Decadal changes show smaller losses increasing while larger amounts are decreasing.

These Storm Data amounts are in strong contrast to insured losses in Colorado, Utah, and Wyoming (Holle et al. 1996). Over a third of those insurance losses were between $251 and $1000, and only a few were over $5000. Storm Data apparently includes more widely known large events and fewer small losses. It is not possible for National Weather Service staff preparing Storm Data to be aware of these numerous small losses when they did not result in a call to an emergency agency or were not reported in a newspaper.

The types of expensive events that reached Storm Data can be indicated by the 17 lightning losses over $5 000 000. Some were due to forest fires in western states, some involved one or more homes destroyed, some were crop loss cases, and some were other single events. Note that the digital database contains 106 entries in 1989 in the damage category of over $500 million. A review of these events in Storm Data indicated they were not capable of producing so large an amount of damage. These erroneously coded events were changed to the “unknown” category.