Several natural disasters such as lightning, hurricanes, floods, and heat waves cause huge human and economic losses every year across the globe. In the 20th century, floods alone resulted in the death of more than 6.62 million people around the world [1
]. French et al. [2
] and Dittmann [3
] reported that flooding was the main event causing weather-related deaths in the United States. Almost 80% of the global 6500 disaster events between 1980 and 2016 that caused fatalities were hydrometeorological [4
]. Flooding is the primary hydrometeorological disaster type that is responsible for hundreds of fatalities across the globe every year (e.g., Chowdhury et al., 1993; Gerritsen, 2005; Borded and Cutter, 2008; Hahn et al., 2017) [5
]. According to the National Weather Service (NWS), floods caused the second highest number of natural disaster deaths after heat waves in the United States [9
]. Different circumstances lead to fatalities during a flooding event. Most flood deaths occur through drowning [10
]. Studies that can focus on certain types of floods that affect a specific region can improve understanding of the hazards and offer new insight to guide investment of resources for mitigation. Terti et al. [11
] studied the circumstances of more than 1000 flash flood fatalities across the US and found that the fatality circumstances have certain characteristics related to season, time of the day, duration of the flood, location, and age and gender groups. Petrucci et al. [12
] studied flood mortality in Mediterranean countries over a 36-year period (1980–2015) and reported that fatalities were increasing, they occurred mostly outdoors, and most of them occurred to people being dragged by water/mud or who were travelling in a vehicle. Diakakis and Deligiannakis [13
] examined flood fatalities in Greece from 1970 to 2010 and found that vehicle-related deaths are the most common type of incident, with drowning being the most common etiology of death.
Vehicle-related flood death was the dominant type among all circumstances in the US. Hamilton et al. [14
] reported that more than half of flood-related deaths were caused by driving through floodwaters. They found that past living experience, individual perceptions of the floodwater hazard, and social and environmental circumstances are the main factors impacting a person’s decision on whether to drive through floodwaters. Drobot et al. [15
] also reported that more than half of all flood fatalities in the United States are vehicle-related, mainly because people who do not treat flood warnings seriously and people who have not experienced floods drive into floodwaters. Ashley and Ashley [16
] asserted that human behavior was a major culprit in flood deaths and that 63% of flood fatalities recorded with occurrence circumstance are vehicle-related. French et al. [2
] found that 42% of drowning deaths were vehicle-related during a study from 1969 to 1981. Zevin [17
] reported that 40% of flash-flood fatalities were related to vehicles or pedestrians crossing streams. Mooney [18
] found that over half of flood fatalities with a known circumstance of occurrence happened in vehicles. Terti et al. [11
] found that more than 60% of the 1075 flash flood fatalities reported from 1996 to 2014 across the United States were related to vehicles involving mainly males. This study found that human vulnerability depends on the social and natural factors of the flash flood; e.g., fatalities related to inundation of permanent buildings were most commonly associated with longer duration events and impacted the elderly, while the young were victims of outdoor activities during short-lived flash floods. In addition to human and social vulnerabilities, Doocy et al. [19
] reported that urbanization, population density, terrain, and storm characteristics are also factors that contribute to flood risk levels. Flood fatality factors that influence human impacts were rural areas, short duration events, small catchment sizes, vehicles, and events that occurred during times with reduced visibility [20
Ahmed et al. [21
] examined the vehicle-related flood fatalities in Australia from 2001 to 2017. It was found that 83% of vehicle-related flood deaths happened when people drove through cross creeks, bridges, or causeways that flooded by rapidly rising floodwater. Drowning was the main category of vehicle-related deaths, resulting in 1.3 fatalities per incident. Half of the incidents occurred at night and 54% of the incidents had only the driver in the vehicle. Age and gender data were identified for drivers and passengers and males significantly outnumbered females. Jonkman and Vrijling [22
] reported that individual behavior and vulnerability are the main factors in flood fatalities. Kellar and Schmidlin [23
] conducted a study on vehicle-related flood fatalities in the United States from 1995 to 2005 and found that more than half of flood fatalities caused by flash floods are vehicle-related. They also found that males were overrepresented by far, especially among those older than 40, in all vehicle-related flood fatalities. The Texas Hill Country was identified as the area with the highest vehicle-related flood fatalities. Vehicle-related flood fatalities could occur at bridges, low water crossings, ditches/culverts, and viaducts or underpasses. Jonkman and Kelman [10
] reported that males were more vulnerable to floodwaters because they were more likely to be involved in unnecessary high-risk behaviors. They also reported that vehicle-related flood deaths occurred most frequently when people attempted to drive across flooded bridges, streams, and roads and these deaths occurred among all phases of flood events (i.e., onset, during, and shortly after). Coates [24
] investigated flood fatalities in Australia from 1788 to 1996 and found that males were more likely to be involved in risky behaviors than females when faced with floodwaters. About 38.5% of all flood fatalities with reported details happened across flooded creeks, bridge, and roads and 31.5% of all flood fatalities were people trapped in a building or camp. Adults and the elderly tend to be more vulnerable, especially in light of the growth of the elderly population in most countries [25
]. When people are trapped inside vehicles in floodwaters, moving waters may sweep vehicles off the road, depending on the water depth and velocity, which are usually underestimated by drivers [26
]. The deeper the floodwater is, the less force or velocity of floodwater is needed to tip a person over. Some people try to escape from their trapped vehicles but are swept away or killed by floating objects [27
Compared to other states in the USA, Texas has been reported to have the highest number of flood fatalities in all studies, e.g., [16
]. Ashley and Ashley (2008) reported a total of 4586 flood fatalities in the USA from 1959 to 2005. Texas (760) had, by far, more flood fatalities than any other state [16
]. Sharif et al. [28
] had similar results, indicating that Texas had 840 flood fatalities from 1959 to 2008. Kellar and Schmidlin [23
] found that Texas is the state with the most storm events (60) and most vehicle-related flood fatalities (107) from 1995 to 2005. Ashley and Ashley [16
] found that the geographic features of Texas lead to a large number of flood fatalities in Texas. Texas is the second largest state in the USA by area (695,662 km²) and population (approximately 29.90 million in 2020). Floods in Texas caused by tropical storms and inland storms relate to different weather patterns such as the North American Monsoon system and movements on cold and warm fronts. The geographic location of the Balcones Escarpment, which consists of a series of cliffs dropping from the Edwards Plateau to the Balcones Fault Line, enhances the formation and increases the efficiency of storms in central Texas. The Gulf of Mexico in the south to the Rocky Mountains in the northwest contribute to the creation of storms capable of producing large amounts of rainfalls. The Texas Hill Country, located on the edge of the Escarpment, is also susceptible to flash floods due to the steep slopes, the very thin topsoil, and large areas of exposed bedrock. Another reason for enhanced runoff in the region is the existence of the highly urbanized corridor extending between the major metropolitan areas Dallas-Fort Worth and San Antonio. This region is known as “Flash Flood Alley”. It includes counties with the fastest population growth rates in Texas (Figure 1
). Construction of large, expensive structures at road-stream crossings in this region is not feasible because there are thousands of these crossing and they stay dry all the time except for occasional storm events. Drainage at these crossings is through culverts and over-the-road flow. Low water crossings throughout Texas, especially in the Hill Country, contribute to road flooding, which poses a significant risk to drivers during flooding conditions [29
Motivated by these findings, this study investigated the vehicle-related flood fatalities in Texas from 1959 to 2019. We will examine, in detail, specific factors within a state that are associated with the highest flood mortality numbers in the US, including vehicle-related fatalities. Moreover, recent years have seen an increase in flood fatalities in Texas, especially in the Houston area. As flood mitigation efforts need to include measures to address risky behavior, we hope that the analysis will contribute to building models of flood resilience for the communities of Texas. The analysis takes into account demographics (age and gender), temporal distributions (annual vehicle-related flood fatalities, month, time of the day), flood types, roadway types, and spatial distribution. The limitations of the database used are described in the summary and conclusions section. The paper discusses factors that may influence the high rate vehicle-related flood fatalities in Texas, compared to other states, and provide information that can help reduce this rate.
2. Data and Methods
is a database maintained by the National Climatic Data Center (NCDC). It includes monthly reports detailing the impacts of severe weather events. The National Weather Service (NWS) started releasing the predecessor of Storm Data
, Climatological Data in 1950. In its early years, the database only collected data on tornadoes and their impacts. Information on thunderstorms and their impact was added after 1955. The name Storm Data
was officially used later in 1959 when data of all severe weather events were added into the database. Emergency management officials, media, insurance companies, and law enforcement are the main sources of data included in Storm Data
]. The database includes different classes of circumstances/location of the deaths or injuries (mostly at a county level), defines the timing of the event by the segment of the day (morning, afternoon, night, etc.), age and gender of victims, and for vehicle-related fatalities, the database includes information about the road type in some cases.
For this study, the data of vehicle-related flood fatalities, which was attributed to coastal floods, flash floods, floods, heavy rain, and tropical storms, was collected from the Storm Data
website for Texas for 1959 to 2019. Fatality data before 1996 was available only as PDF files. In total, 444 Storm Data
reports in PDF format were reviewed (1959–1995). Rainfall data was obtained from the National Centers for Environmental Information (NCEI) of the National oceanic and Atmospheric Administration [32
]. Texas flood fatality data was downloaded for each year and then combined. In-house R scripts were developed to extract data needed for the analysis. R scripts were used to run Mann-Kendall nonparametric trend analysis. Excel was used to perform analysis of variance (ANOVA) to compare variables such as gender. R scripts were used to process rainfall data and compare rain and fatality data.
4. Discussion and Conclusions
In this study, the data of vehicle-related flood fatalities in Texas from 1959 to 2019 has been examined in detail. Temporal and spatial patterns of vehicle-related flood fatalities, the circumstances when vehicle-related flood death occurrs, the demographic characteristics of victims, the type of floods leading to fatalities, and roadway types where vehicle-related flood deaths occurred were included in the analysis. A total of 570 vehicle-related flood deaths occurred in Texas during the 61-year study period. All but three events resulted in a single fatality. These fatalities represent 58% of the total flood fatalities. Providing the details of vehicle-related flood deaths can help officials and the public to better understand flood hazards. Furthermore, policy makers and engineers can have a better estimation of the flood impacts and take corresponding proactive mitigation measures. Resources can be invested strategically to improve the effectiveness of education programs by specifically targeting vulnerable groups. Financial resources can be directed to emergency preparedness hazard communication and address immobility issues.
The annual distribution of these fatalities was similar to that of the general flood fatalities. Both types of fatalities show statistically significant decreasing trends, indicating that population growth in Texas far outpaces the number of flood fatalities, helping to decrease the normalized fatality rates. The downtrend in normalized fatalities may be partially attributed to improvement in official flood warning systems or emergency responses. Also, community awareness efforts such as the “Turn Around Don’t Drown” campaign and the repeated exposure of Texans to major flood events may have modified their flood risk perceptions or improved their risk awareness, leading to more conscious decisions during flooding. Monthly distribution of vehicle-related fatalities follows that of rainfall in the Flash Flood Alley, similar to that of all flood fatalities reported by Sharif et al. [22
]. Flash flood caused 61% of all vehicle-related flood fatalities and most of them (more than 80%) occurred in the Flash Flood Alley region. The high risk in this region can be reduced by investment in roadway flood safety improvement, including early warnings, better road flooding signage, indicating alternate routes during flooding, and preemptive transportation protocols. Topography, weather, and land surface characters combine to initiate flash floods, which catch people off-guard due to their rapid development [16
]. Night accounted for 45% of the total vehicle-related deaths among all the times of day. Mooney [14
] found that nearly 75% of flash flood deaths occurred during darkness hours with low visibility.
Males made up a greater percentage of flood victims than females, 62% to 38%. This result agrees with previous studies suggesting that males were more likely to take risks during a flood event [10
]. The most vehicle-related flood deaths occurred in the age group of 20–29 years for both male and female victims; possibly, because people in this age group underestimate the hazard of floodwaters and overestimate their driving skills and the protective capability provided by their vehicles. Education programs should be tailored to male drivers in this age group. Old drivers are less likely to drive in inclement conditions [41
], which is supported by the results of this study. It is clear that social psychological factors (e.g., attitudes and social norms) should guide efforts aimed at improving individuals’ behavioral decisions during flood situations [42
]. Gender-specific educational programs may also be of help [10
]. Evidence from Australia showed the effectiveness of such approaches [10
Individual behavior also plays an important role in affecting vehicle-related flood fatalities. It seems that many people underestimate the destructive power of floodwaters and overestimate their driving skills and the protective capability of their vehicles. Rescuing personal properties, rescuing people without professional training, working for emergency and support services, and driving to a specific destination were among the reasons people drive into floodwaters intentionally. Drivers in fatal crashes frequently failed to follow the warning signs and indicators. Drobot et al. [15
], using data from survey questionnaires conducted in Denver and Austin, found that people who do not take flood warning signs seriously, who did not experience floods previously, and who are not aware that the area they live in is flood-prone are more likely to drive into floodwaters. Hamilton et al. [14
] found that experience, individual perceptions, and social and environmental context were the main factors that influenced people in making the decision to drive through floodwaters. Since it is not easy to assess the severity of flood conditions as they evolve, motorists seek additional sources of information and weigh the dangers against other situational factors on a case-by-case basis, such as their prior successful crossing of other vehicles, road signage and barricades, presence of passengers, and their perceived risk of personal injury or damage to their vehicle [43
]. All these factors should be included in educational programs.
It is important to address the misconception that vehicles, especially light trucks and SUVs, can safely cross flood roads and creeks. The Federal Emergency Management Agency [44
] reported that six inches of floodwater can reach the bottom of most passenger vehicles and then drivers will lose control of their car, either due to the engine stalling or the force of the flowing water. Two feet of rushing water can lift and float most cars, including sport utility vehicles and pick-ups in a short time. Moreover, often vehicle occupants had little time to escape when vehicles were trapped and submerged in floodwater in most situations. This misconception has been discussed by some other researchers in some other regions [20
]. Similar research can be conducted in Texas in the future to estimate the water depth and velocity condition for some of the cases of vehicle fatalities, especially in the Flash Flood Alley. Results of such studies can be included in driver license manuals and defensive driving classes. Additionally, transportation agencies and insurance companies can alert the public about the flood hazards with the recorded cases of vehicle-related flood fatalities without releasing personal information. Auto manufacturers can participate in the education program to introduce vehicle performance in different weather conditions.
It is clear that Storm Data
is not a completely perfect source for the details of vehicle-related flood fatalities, mainly due to the inconsistency of the details recorded. This may be because the information is collected from different sources, including the media. For example, details of location, demographics, and time are missing for many incidents. Moreover, there are some conflicts in the descriptions of the flood type fatalities with fatalities resulting from tropical storms being attributed randomly to the storm or the ensuing flooding. When the roads cross a creek, the location is specified as only either a creek or a road. However, Storm Data
is the most comprehensive and primary source for vehicle-related flood fatality data [3
]. Similarly, Ahmed et al. (2020) found that data from the Australian National Coronial Information System (NCIS) suffered from inconsistencies and missing details [21
]. The authors hope that the NWS can use the feedback from this and previous studies in Storm Data
to improve the quality of the information in this invaluable source.