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NOAA By the Numbers Topics

Severe Storms, Tornadoes, and Flash Flooding

A thunderstorm releases lightning, usually caused by convection through surface heating, and may lead to fires, property damage, and fatalities. A thunderstorm is classified as “severe” when it contains one or more of the following: hail one inch or greater, winds gusting in excess of 50 knots (57.5 mph), or a tornado. As thunderstorms worsen to tornadoes, even the most resilient structures are at risk. According to the NWS Storm Prediction Center there were 1,791 tornadoes in 2024 in the United States with 54 tornado-related deaths.

The most significant risk to human life from a thunderstorm, however, is flash flooding.   Flash floods occur when heavy rainfall exceeds the ability of the ground to absorb it and can happen within minutes. Flash flooding claims more lives per year than any other thunderstorm related hazard with most fatalities caused by vehicular-related drownings.

NOAA's Role:

  • Research and Development:
      • The NOAA National Severe Storms Laboratory (NSSL), located in Norman, Oklahoma, serves the nation by working to improve the lead time and accuracy of severe weather warnings and forecasts to save lives and reduce property damage. 
      • NOAA NWS forecasters utilize Geostationary Lightning Mapper (GLM) data alongside radar to identify “lightning jumps,” or rapid increases in flash rates, which often signal that a storm’s updraft is intensifying and a tornado may be imminent. This capability is particularly valuable for issuing earlier warnings during radar outages or in regions where radar coverage is limited due to terrain. – Rudlosky, S., S. Goodman, K. Calhoun, C. Schultz, A. Back, B. Kuligowski, S. Stevenson, and C. Gravelle. (2020). Geostationary Lightning Mapper Value Assessment, NOAA Technical Report NESDIS 153. https://repository.library.noaa.gov/view/noaa/27429 
    • National-Level Forecasting and Watches:

Why It Matters:

Severe Storms

Fatalities
  • NOAA NWS issues severe storm/thunderstorm warnings which protect the public by encouraging sheltering, reducing potential casualties:
      • The NWS NEXRAD weather radar network, used by NWS forecasters in thunderstorm predictions and warnings, lead to reductions in casualties from severe nontornadic thunderstorm winds valued at $217 million (2023$) per year. When combined with tornado and flash flood benefits, the total annual value of the radar network for mitigating casualty threats exceeds $1.17 billion. – Rudlosky, S. D., Patton, J., Palagonia, E., Cho, J. Y. N., & Kurdzo, J. M. (2024). Radar Outage Costs and the Value of Alternate Datasets. Weather and forecasting, 39(6), 867-879. https://doi.org/10.1175/WAF-D-23-0165.1
      • In Maimi-Dade, Florida, severe storms/thunderstorms caused 7.04 injuries and 3 fatalities. Out of 63 events that occurred between 1960-2019, 36.5% were compound events with lightning, precipitation, and river discharge being the main drivers. These results were based on historical socio-economic loss data from Spatial Hazard Events and Losses Database for the United States (SHELDUS) and hydrometeorological data from reanalysis datasets.  – Ali, J., Wahl, T., Enriquez, A. R., Rashid, M. M., Morim, J., Gall, M., & Emrich, C. T. (2023). The role of compound climate and weather extreme events in creating socio-economic impacts in South Florida. Weather and Climate Extremes, 42, Article 100625. https://doi.org/10.1016/j.wace.2023.100625
  • In Miami-Dade, Florida, severe storms/thunderstorms caused $10.24 million (2019$) in property damage. Out of 63 events that occurred over this period, 36.5% were compound events with lightning, precipitation, and river discharge being the main drivers. These results were based on historical socio-economic loss data from Spatial Hazard Events and Losses Database for the United States (SHELDUS) and hydrometeorological data from reanalysis datasets. – Ali, J., Wahl, T., Enriquez, A. R., Rashid, M. M., Morim, J., Gall, M., & Emrich, C. T. (2023). The role of compound climate and weather extreme events in creating socio-economic impacts in South Florida. Weather and Climate Extremes, 42, Article 100625. https://doi.org/10.1016/j.wace.2023.100625    

Tornadoes

Fatalities
  • NOAA NWS issues tornado warnings which protect the public by encouraging sheltering, reducing potential fatalities:
    • In the contiguous United States there are 143 operational Weather Surveillance Radar-1988 Doppler (WSR-88Ds) which forecasters use to detect and deliver tornado warnings to the public. The benefits of the WSR-88Ds from tornado detections and warnings (relative to no radar coverage) include: (1) a reduction in annual fatalities valued at $147.4 million (2018$), (2) a reduction in annual injured people (hospitalized and treated and released) valued at $315.1 million, and (3) a reduction in lost time from false alarm sheltering valued at $22.0 million. Results were based on tornado warning data from the Iowa Environmental Mesonet NWS Watch/Warnings archive and tornado event data from NOAA NCEI’s storm events database between 1998-2017.  – Cho, J. Y. N., & Kurdzo, J. M. (2019). Weather Radar Network Benefit Model for Tornadoes. Journal of Applied Meteorology and Climatology, 58(5), 971-987. https://doi.org/10.1175/JAMC-D-18-0205.1  
    • The NWS NEXRAD network was estimated to provide $596 million (2023$) in annual benefits for mitigating tornado casualties and reducing time lost to sheltering. Additionally, during radar outages—which occur on average 9 days per year per radar—alternative datasets such as satellite imagery provide approximately $29.1 million in annual value by helping forecasters mitigate the loss of radar coverage. – Rudlosky, S. D., Patton, J., Palagonia, E., Cho, J. Y. N., & Kurdzo, J. M. (2024). Radar Outage Costs and the Value of Alternate Datasets. Weather and forecasting, 39(6), 867-879. https://doi.org/10.1175/WAF-D-23-0165.1 
    • Two recent studies provide the first general estimates of tornado casualty rates (injuries and fatalities) across the U.S. The studies used 22 and 24 years (1995-2016 and 1995-2018) of tornado-level data to overlay damage paths with fine-scale population and housing unit data and calculated rates based on the number of people and buildings actually exposed to the storm. Accordingly, the overall estimated national per-capita casualty rate was estimated to be 2.3% and the national per-housing unit casualty rate was estimated to be 5.4%. Further disaggregated results showed that while the national per-capita fatality rate was 0.15%, the national per-housing unit fatality rate was 0.36%. Similarly, the national per-capita injury rate was 2.1% and the national per-housing unit injury rate was 5.1%. The studies showed that tornadoes account for the third-highest average annual weather-related fatality rate in the U.S. (trailing only extreme heat and floods), killing an average of 74 people per year. Over the 24-year study period (1995-2018), tornadoes caused 1,775 fatalities and 25,959 total casualties (combined injuries and fatalities or deaths). – Fricker, T. (2020). Evaluating tornado casualty rates in the United States. International Journal of Disaster Risk Reduction, 47, 101535. https://doi.org/10.1016/j.ijdrr.2020.101535 ; Fricker, T., & Friesenhahn, C. (2022). Tornado Fatalities in Context: 1995-2018. Weather Climate and Society, 14(1), 81-93. https://doi.org/10.1175/WCAS-D-21-0028.1
    • How information regarding tornado warnings is communicated to those that might be affected by tornadoes is crucial as those affected can take steps such as sheltering appropriately to mitigate its impact on health. Most people in a tornado strike zone will take shelter while those in the warning zone may or may not. A survey within tornado prone areas showed that information regarding probabilities of experiencing a tornado would make people more likely to take protective measures when compared to a simple deterministic warning. The survey found that a simple warning would prevent 19 deaths per year while the probabilistic warning would prevent 26 deaths per year. With the only consideration of impact being lives saved and using statistical value of life, the U.S. would value the deterministic warning at $250 million per year (2023$) and the probabilistic warning at $335 million per year.  – Ugarov, A. (2023). Lives Saved versus Time Lost: Direct Societal Benefits of Probabilistic Tornado Warnings. Weather Climate and Society, 15(3), 587-602. https://doi.org/10.1175/WCAS-D-22-0139.1 
  • Tornadoes have been shown to cause millions in property damages, reduce housing price values, and stunt housing price growth:
    • In Florida, between 1950-2015, there were 3,233 reported tornadoes. During this period $171 million (2014$) in property values were exposed to tornadoes with $103 million coming from residential properties alone. As property values exposed to tornadoes increase so too does property losses–between 2007-2015, a doubling of residential property exposure was found to increase actual recorded losses by 26% and a doubling of nonresidential property exposure was found to increase losses by 21%. Results were based on property value data from Florida’s Department of Revenue and historical tornado data from the NOAA NWS Storm Prediction Center. – Elsner, J. B., Ryan, E., & Strode, G. (2018). Structural Property Losses from Tornadoes in Florida. Weather, Climate, and Society, 10(2), 253-258. https://doi.org/10.1175/WCAS-D-17-0055.1   
    • Between 1991-2015, the U.S. experienced 1,224 tornadoes on average, annually, with the greatest number of tornadoes occurring in Kansas, Oklahoma, and Texas (annual averages of 92.4, 65.4, and 146.7). Tornadoes were found to negatively affect housing price growth at the MSA level within 1-month of their occurrence, whether they occurred within the MSA or in a neighboring MSA. At the regional-level, in the south, tornadoes were found to account for a significant 14.61% drop in house price levels, and, in the midwest, tornadoes were found to account for a smaller 5.59% drop in house price levels, both over a 5-year period. Results were based on housing price indices from the FreddyMac House Price Index (at the MSA-level) and US Census Bureau (at the regional-level), and tornado events from NOAA NWS Storm Events Database between 1975-2019. – Donadelli, M., Jüppner, M., Paradiso, A., & Ghisletti, M. (2020). Tornado activity, house prices, and stock returns. NORTH AMERICAN JOURNAL OF ECONOMICS AND FINANCE, 52, Article 101162. https://doi.org/10.1016/j.najef.2020.101162
    • Areas repeatedly exposed to a tornado experience long-term negative effects on median home value and rent. Between 1980 to 2010, 6,026 census tracts experienced at least one tornado with 2,677 having received at least one severe tornado. When matched with census tracts that were similar in pre-tornado socio-economic characteristics for the period, all tornado affected areas on average saw a median housing price decline of $2,468 (2010$), while repeatedly affected areas saw a decline of $9,976. On average a $28 lower monthly rental value was seen for the latter group when compared to the similar non-affected tracts. Those affected by a single but a severe tornado saw a $4,133 decrease in average housing price. For the overall sample, significant decline in median housing prices occurs at least 20 years after the event; for those areas with multiple tornados, the significant decline is sooner after the second tornado and sees a continuing decline. A similar trend is observed for those affected by at least one severe tornado. The effect of disaster lasts well beyond physical recovery and reconstruction of housing units and other infrastructure. – Read, A. (2025). Repeated disaster and the economic valuation of place: temporal dynamics of tornado effects on housing prices in the United States, 1980-2010. Population and Environment, 47(3), Article 29. https://doi.org/https://doi.org/10.1007/s11111-025-00502-w

Flash Floods

Fatalities
  • NOAA NWS issues flash flood warnings which protect the public by encouraging sheltering, reducing potential fatalities:
      • According to the NWS Storm Events database, a total of 74,814 flash flood events occurred in the U.S. between 1996-2017. Approximately 1.2% of these flash flood events were found to cause fatalities (1,399 in total) with Hurricane Harvey (2017) leading to the greatest number of fatalities at 55 deaths. The regions most prone to flash flooding and fatalities were in the southwest (Arizona and southern California), southern plains (central Texas, Oklahoma, Arkansas, and Missouri) and parts of the northeast (New York and Pennsylvania). Flash flood events were found to occur with increasing frequency over time with a greater number of flash floods and fatalities during the spring and summer months.  – Ahmadalipour, A., & Moradkhani, H. (2019). A data-driven analysis of flash flood hazard, fatalities, and damages over the CONUS during 1996-2017. JOURNAL OF HYDROLOGY, 578, Article 124106. https://doi.org/10.1016/j.jhydrol.2019.124106 
      • A study over a 60-year period (1959-2019) provides a comprehensive analysis of the circumstances and demographics surrounding flood-related deaths involving vehicles in Texas. Overall, a total of 570 vehicle-related flood fatalities were recorded over the study period, representing 58% of all flood-related deaths in Texas. Flash flooding was responsible for 347 (61%) of all vehicle-related flood fatalities. However, both total flood fatalities and vehicle-related fatalities showed statistically significant decreasing trends during this period. – Han, Z. Y., & Sharif, H. O. (2020). Vehicle-Related Flood Fatalities in Texas, 1959-2019. Water, 12(10). https://doi.org/10.3390/w12102884 
      • A study examines the characteristics and trends of flood-related deaths in the United States over a 60-year period (1959-2019). A total of 6,478 flood fatalities occurred in the contiguous United States during this period. Texas experienced the highest number of fatalities by a significant margin (1,069). Other top states included Louisiana (693), California (339), Pennsylvania (277), Mississippi (266), and Virginia (265). The study identified “Flash Flood Alley” in Texas and the Gulf Coast region as major clusters for flood-related deaths. Flood fatalities peaked during the summer months, with July (1,019), June (943), and August (803) recording the highest numbers. Regarding flood types, flash flooding was the deadliest category with 2,249 fatalities (41.80%), followed by general flooding events with 1,414 deaths (26.28%), rain-related flooding with 632 deaths (11.75%), and tropical systems such as hurricanes and storms which accounted for 574 deaths (10.67%). – Han, Z. Y., & Sharif, H. O. (2021). Analysis of Flood Fatalities in the United States, 1959-2019. Water, 13(13), Article 1871. https://doi.org/10.3390/w13131871
      • The U.S. weather radar network, used by NWS forecasters in flash flood predictions and warnings, lead to reductions in fatalities valued at $289.9 million (2019$) per year and reductions in injured people (hospitalized and treated and released) valued at $26.3 million per year, relative to no radar coverage. Results were based on storm warning data from the Iowa Environmental Mesonet NWS Watch/Warnings archive and flash flood data from the NOAA U.S. Flash Flood Observation Database between 2007-2018. – Cho, J. Y. N., & Kurdzo, J. M. (2020). Weather Radar Network Benefit Model for Flash Flood Casualty Reduction. Journal of Applied Meteorology and Climatology, 59(4), 589-604. https://doi.org/10.1175/JAMC-D-19-0176.1  
  • Flash floods, which historically have been increasing in frequency over time, can cause significant property damage:
    • According to the NWS Storm Events database, a total of 74,814 flash flood events occurred in the U.S. between 1996-2017. Flash flood frequency and property damage was found to increase over this period with total property damages, excluding damages from Hurricane Harvey, amounting to $37.3 billion (2017$)–Flash flood property damages of Hurricane Harvey alone were found to exceed $38.3 billion. In general, the costliest property damages from flash floods were found to occur in September and October, during the Atlantic hurricane season.  – Ahmadalipour, A., & Moradkhani, H. (2019). A data-driven analysis of flash flood hazard, fatalities, and damages over the CONUS during 1996-2017. JOURNAL OF HYDROLOGY, 578, Article 124106.
    • A study developed a model to predict potential property damages (i.e., lost value and cost of repairs) from flash flooding in Texas. When applying the model to Harris County, the study found that, for 12- and 24-hour flash floods, some communities (high value homes in urbanized areas) could expect millions of dollars (2019$) in property damages. For shorter 6-hour extreme rainfall events the study found property damages up to $10,000. In general, flash flood damages were influenced by how soon runoff collection could occur, floodwater flow velocity, and floodwater depth. The model was developed based on a flash flood data set (2,866 flood events) for a 15-year period (2005–2019) from NOAA’s storm events database.  – Chang, S., Singh Wilkho, R., Gharaibeh, N., Lyle, S., & Zou, L. (2023). Predicting flash flood economic damage at the community scale: Empirical zero-inflated model with semicontinuous data. Natural Hazards Review, 24(4), 04023030. https://doi.org/https://doi.org/10.1061/NHREFO.NHENG-1729