FLOOD06680

• County: Statewide
• Basin: Statewide
• Title: Flood Damage in the United States, 1926-2000
• Date: 6/1/2000
• Prepared By: NOAA
• Floodplain - Doc Type: Flood Documentation Report

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probably consider the floods of 1997 to be much more severe than those of 1993, while farmers
might hold the opposite view.

Caution #3: Because of the large estimation errors found in the NWS data, estimatesfor
individual floods should be used with caution. For some purposes the comparison of individual
floods may be better done using nominal or ordinal data categorizations. For specific events,
detailed descriptions should be sought to compare the nature and impacts of the damage.

D. Possible Inconsistencies With Other Sources
The NWS defines flood damage more narrowly than many other agencies. Emergency
management agencies generally include both river and coastal flooding whenever water rises to
overflow land that is not normally submerged. In contrast, the NWS estimates include only
flooding whose primary cause is rainfall, snowmelt, or river flows, excluding flooding caused by
wind-driven waves associated with coastal storms or hurricanes. For example, FEMA records
show a Presidential disaster declaration of type "flood" for Massachusetts in February 1978, and
the USACE reports $520 million flood damage due to storm surge and huge waves (US ACE
New England Division 1979; converted to 1995 dollars), but that damage is not included in NWS
flood damage estimates.

The NWS estimates do include floods caused by dam failure, however. In the NWS
record, Idaho's worst flood resulted from the failure in 1976 of the newly-constructed Teton
Dam, with damage estimates in the $1- 2.3 billion range (in 1995 dollars). Idaho's largest
estimated flood damage due to natural causes was much smaller: $120 million in 1997.

Caution #4: Different agencies define "flood" and "flood damage" somewhat differently.
Check for incompatibilities between data from different sources before seeking to combine
sources or aggregate data.

E. Uses of the Reanalyzed NWS Damage Estimates
With the precautions noted above, we conclude that the reanalyzed NWS flood damage
estimates can be a valuable tool to aid researchers and decision makers in understanding the
changing character of damaging floods in the United States. Data sets of annual damage at
national, state, and river basin levels are available at www.flooddamagedata.org.

In climate research, these data can contribute to understanding the relationship between
climatic influences and damaging floods. For example, they have been used to examine the
relationship of national and regional flood damage with several measures of precipitation, in a
study that controlled for changes in population and wealth (Pielke and Downton 2000). For
policy makers and emergency managers, the data provide a nationwide overview of flood
vulnerability and can be useful in evaluating policies related to management of flood hazards.
For example, we have investigated the role of politics in presidential disaster declaration
decisions by comparing disaster declarations involving floods with estimated flood damage
(Downton and Pielke 2001).

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