Frequently Asked Questions

Even though $1B is an arbitrary threshold, these specific events account for the majority (>80%) of the damage from all recorded U.S. weather and climate events (NCEI; Munich Re). In fact, these billion-dollar disaster events are becoming an increasingly larger percentage of the cumulative damage from the full distribution of weather-related events at all scales and loss levels.

This mapping tool is intended to provide U.S. communities with information and guidance on their susceptibility to weather and climate hazards, as well as potential future impacts from them. This tool could assist with: Enhancing hazard preparation and mitigation for homeowners, community planners and emergency managers; Encouraging community-level risk communication and planning; Guiding communities' building codes and standards; Informing disaster resilience and recovery plans in the long term. This mapping tool gives broad, nationwide comparisons reflecting a county's combined physical exposure, vulnerability and resilience to hazard risks. These county maps may not be as accurate as locally available data, and users with access to local data for each risk component should consider substituting those data to calculate a more precise annual loss values at the local levels. For example, finer detailed risk analysis would require more spatially and temporally granular data for hazard exposure, annualized frequency, and historic loss measurements. This mapping also does not consider the complex economic and physical interdependencies that exist across geographic regions. For example, a disaster's impact on one location can cause indirect losses in surrounding counties. Given these caveats, the county risk mapping should be considered a baseline measurement and a guideline for determining natural hazard risk but should not be used as an absolute measurement of risk.

Yes, the number and cost of disasters are increasing over time due to a combination of increased exposure (i.e., values at risk of possible loss), vulnerability (i.e., where we build; how we build) changes in the frequency of some types of extremes that lead to billion-dollar disasters. More specifically, these trends are further complicated by the fact that much of the growth has taken place in vulnerable areas like coasts and river floodplains. Vulnerability is especially high where building codes are insufficient for reducing damage from extreme events. Climate variability can alter frequency of some types of extreme weather that lead to billion-dollar disasters - most notably the rise in vulnerability to drought, lengthening wildfire seasons in the Western states, and the potential for extremely heavy rainfall becoming more common in the eastern states.

A county's risk depends on several factors, including its population, its infrastructure (i.e., the number of homes, businesses, vehicles, crops, etc.) that could be vulnerable, and its physical exposure to natural hazards. Vulnerability reflects a county's reduced ability to prepare for, respond to, and recover from hazards based on many socioeconomic factors.

No. The intent of these maps is to depict broad-scale patterns of physical exposure, vulnerability and resilience to hazards. Risk-based calculations should be based on more local-scale data. As an example, property insurance companies often seek more detailed data granularity—much finer than at the county scale—to determine physical hazard risk in developing insurance premium cost. The National Risk Index hazard risk scores within this product do not provide that level of detail and should not be used when making insurance premium cost determinations.

Yes, every state in the country has been impacted by at least one billion-dollar disaster since 1980. Since 1980, there have been more than 100 of these events that have affected at least some part of Texas, while only one event has impacted Hawaii (Hurricane Iniki in 1992). The Central, South, and Southeast regions typically experience a higher frequency of billion-dollar disasters than other regions.

Some of the data sources we use include proprietary insurance data, which preclude it from being shared. The cost ranges are a means of providing a comparison of this data without compromising the underlying data.

Yes, the U.S. has experienced an increase in billion-dollar, non-hurricane, inland flood disasters (i.e., from extreme rainfall, riverine flooding) in the last decade (18 floods during 2010-2019) than during the prior 3 decades combined (15 floods during 1980-2009).

The maps integrate individual and multiple hazard types for historic risk and offer future projections for different socioeconomic variables for every county. These maps also combine information in relation to county population, crop and infrastructure value exposure in addition to vulnerability and resilience to hazards, in determining baseline risk at a county scale for many hazard types. These maps also provide future risk projections (RCP 8.5 high greenhouse emission scenario) for select socioeconomic variables at the county scale.

Yes, these maps integrate individual and multiple hazard types for historic risk and offer future projections for different socioeconomic variables for every county. We have leveraged and expanded upon FEMA's National Risk Index to provide over 100 interactive U.S. county hazard maps for any combination of county-level hazard risk including: hurricanes, severe storms (tornado, hail, damaging winds), inland / urban flooding, drought / heat wave, wildfire, winter storms and freeze/cold wave events. This includes many unique hazard combinations, which are useful in a new era of more likely cascading hazard impacts (i.e., drought-enhanced wildfires produce mountain-side burn scars, which often enhance debris flows from flooding, as we often see in California). For example, the following 'Drought, Flooding and Wildfire' risk map is a new multi-hazard, combined risk map not previously accessible.

1980 is the beginning of the first decade in which most all of the public and private sector disaster data resources we use become available.

Yes, we introduce events into the time series as they "inflate" their way above $1B in costs in today's dollars. Every year, this leads to the introduction of several new events added from earlier in the time series.

The Consumer Price Index (CPI) is one of many indices to measure inflation. Other indices can also be used for comparison, which is why we also provide unadjusted disaster costs.

Yes, our disaster mapping section provides new socioeconomic vulnerability data for each county, using CENSUS / American Community Survey data. This new mapping enhancement offers county data for: percent of Population Living below Poverty, Per Capita Income, percent Population with Disability, percent Households with No Vehicle, percent aged 65 Years and Older, percent Minority Population, percent Mobile Homes, among other data. This information can be compared with county weather and climate hazard risk scores or projected future socioeconomic vulnerability from climate variability.

More than one dozen public and private sector data sources help capture the total, direct costs (both insured and uninsured) of the weather and climate events. These costs include: physical damage to residential, commercial, and municipal buildings; material assets (content) within buildings; time element losses such as business interruption or loss of living quarters; damage to vehicles and boats; public assets including roads, bridges, levees; electrical infrastructure and offshore energy platforms; agricultural assets including crops, livestock, and commercial timber; and wildfire suppression costs, among others. However, these disaster costs do not take into account losses to: natural capital or environmental degradation; mental or physical healthcare related costs, the value of a statistical life (VSL); or supply chain, contingent business interruption costs. Therefore, our estimates should be considered conservative with respect to what is truly lost, but cannot be completely measured due to a lack of consistently available data.

Links to key public sector data sources include FEMA Public Assistance, FEMA Individual Assistance, USDA Risk Management Agency Crop Indemnity, the USDA National Agricultural Statistics Service, the National Interagency Fire Center wildfire data, the National Flood Insurance Program claims data and the NOAA Storm Events Database. We also reference state insurance services such as CalFire and FLOIR, the U.S. Department of Defense disaster impact reports, the Federal Highway Administration damage reports and private property insurance data as part of this event analysis. We also examine insurance penetration rates for vehicle insurance, home insurance, flood insurance, crop insurance, and business coverage, to better understand insured and uninsured assets. In addition, we incorporate socioeconomic risk information from the Census American Community Surveys, the CDC Social Vulnerability Index, among others that provide additional spatial context of hazard risk. In addition, we incorporate socioeconomic risk information from the Census American Community Surveys, the CDC Social Vulnerability Index, among others that provide additional spatial context of hazard risk.