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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EXECUTIVE SUMMARY

Flood damage continues to increase in the United States, despite extensive flood
management efforts. To address the problem of increasing damage, accurate data are needed on
costs and vulnerability associated with flooding, Unfortunately, the available records of
historical flood damage do not provide the detailed information needed for policy evaluation,
scientific analysis, and disaster mitigation planning,

This study is a reanalysis of flood damage estimates collected by the National Weather
Service (NWS) between 1925 and 2000, The NWS is the only organization that has maintained
a long-term record of flood damage throughout the U,S, The NWS data are estimates of direct
physical damage due to flooding that results from rainfall or snowmelt. They are obtained from
diverse sources, compiled soon after each flood event, and not verified by comparison with
actual expenditures, Therefore, a primary objecti ve of the study was to examine the scope,
accuracy, and consistency of the NWS damage estimates to improve the data sets and offer
recommendations on how they can be appropriately used and interpreted,

This report presents the following three data sets, which are also available on the World
Wide Web at www,flooddamagedata,org:

. Estimated flood damage in the D,S, (1926-1979 and 1983-2000, by fiscal year;
· Estimated flood damage for each state in the U.S, (1955-1979, by calendar year, and
1983-2000, by fiscal year); and
· Estimated flood damage, by river basin, for the U,S, (1933-1975, by calendar year),

We found that the NWS collection and processing of flood damage data were reasonably
consistent from 1934 to the present, except during the period 1976-1982, Data from NWS files
and other sources made it possible to reconstruct state and national flood damage estimates for
1976-1979, However, little data was collected during 1980-1982 and large errors were
discovered in estimates developed later for that period, As a result, the years 1980-1982 are
excluded from the reanalyzed data sets:

Evaluation of the accuracy of the estimates led to the following conclusions:

1. Individual damage estimates for small floods or for local jurisdictions within a larger
flood area tend to be extremely inaccurate, When damage in a state is estimated to be less than
$50 million (in 1995 dollars), estimates from NWS and other sources frequently disagree by
more than a factor of two,

2, Damage estimates become more accurate at higher levels of aggregation. When
damage in a state is estimated to be greater than $500 million, disagreement between estimates
from NWS and other sources are relatively small (40% or less). The relatively close agreement
between NWS and state estimates in years with major damage is reassuring, since the most
costly floods are of greatest concern and make up a large proportion of total flood damage,

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