Severe Thunderstorms and Tornadoes in the United States

Peter Folger
Specialist in Energy and Natural Resources Policy

Severe thunderstorms and tornadoes affect communities across the United States every year, causing fatalities, destroying property and crops, and disrupting businesses. Tornadoes are the most destructive products of severe thunderstorms, and second only to flash flooding as the cause for most thunderstorm-related fatalities. Damages from violent tornadoes seem to be increasing, similar to the trend for other natural hazards—in part due to changing population demographics and more weather-sensitive infrastructure—and some analysts indicate that losses of $1 billion or more from single tornado events are becoming more frequent. Insurance industry analysts state that tornadoes, severe thunderstorms, and related weather events have caused nearly 57%, on average, of all insured catastrophe losses in the United States in any given year since 1953. 

Policies that could reduce U.S. vulnerability to severe thunderstorms and tornadoes include improvements in the capability to accurately detect storms and to effectively warn those in harm's way. The National Weather Service (NWS) has the statutory authority to forecast weather and issue warnings. Some researchers suggest that there are limits to the effectiveness of improvements in forecasting ability and warning systems for reducing losses and saving lives from severe weather. The research suggests that, for example, social, behavioral, and demographic factors now play an increasingly important role in tornado-related fatalities. 

At issue for Congress is its role in mitigating damages, injuries, and fatalities from severe thunderstorms and tornadoes. The National Science and Technology Council has recommended the implementation of hazard mitigation strategies and technologies, including some—such as conducting weather-related research and development and disseminating results—that Congress has supported through annual appropriations for the National Oceanic and Atmospheric Administration, the National Science Foundation, the Federal Emergency Management Agency, the National Aeronautics and Space Administration, and other federal agencies. Other recommended strategies include land use and zoning changes, which are typically not in the purview of Congress. 

Congress attempted to clarify the federal role in mitigating damages from windstorms (including tornadoes and thunderstorms) by passing the National Windstorm Impact Reduction Act of 2004 (P.L. 108-360). It is not evident whether the program made progress toward its objective: achievement of major measurable reductions in the losses of life and property from windstorms. Authorization for the program expired at the end of FY2008. Stand-alone legislation (H.R. 2627) to reauthorize the program was introduced on May 21, 2009. On October 15, 2009, H.R. 3820, the Natural Hazards Risk Reduction Act of 2009, was introduced to reauthorize the National Earthquakes Hazards Reduction Program (Title I) and the wind hazards program (Title II) through FY2014. H.R. 3820 was ordered to be reported by the House Science and Technology Committee on October 21, 2009. 

It is not clear whether changes to climate over the past half-century have increased the frequency or intensity of thunderstorms and tornadoes. An issue for Congress is whether future climate change linked to increases in greenhouse gas emissions will lead to more frequent and more intense thunderstorms and tornadoes, and whether ongoing efforts by Congress to mitigate longterm global warming will reduce potential future losses from thunderstorms and tornadoes.


Date of Report: February 2, 2010
Number of Pages: 24
Order Number: R40097
Price: $29.95

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