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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2. Review of data collection and reporting methods used by the NWS.
In interviews, staff of NWS-HIC and two NWS field offices described their data and
recent data collection procedures, NWS-HIC documents and several editions of the NWS
Operations Manual provided additional information on past and present procedures, This report
describes the nature of the damage estimates and provides a guide to their interpretation and use.

3. Evaluation of accuracy and consistency of the damage estimates.
This report critically examines criteria and methods used by the NWS in collecting past
and present damage estimates to identify likely sources of inaccuracy, To understand the
inaccuracy generally inherent in damage estimation, the report uses statistical comparison
methods to assess a Califomia data set containing both preliminary damage estimates and actual
cost information, Then it uses similar statistical methods to compare NWS damage estimates
with independent estimates from state sources to evaluate the variability in flood damage
estimates, Finally, it assesses the impacts of errors and omissions on aggregated damage
estimates,

4. Development of guidelines for use of the data.
Evaluation results show substantial errors in many of the damage estimates. Uncertainty
about the accuracy of the estimates implies that comparisons of flood damage estimates from
different flood events or different locations must be undertaken with caution, The report
presents examples that illustrate appropriate and inappropriate ways of using the damage data
and suggests ways of reducing the impact of errors,

The data and an associated Users Guide are available on the World Wide Web, at
www.flooddamagedata.org,

E. Organization
This report is organized as follows, Section 2 describes NWS procedures for obtaining
damage estimates and other sources used in compiling the reanalyzed data sets, Section 3
presents the reanalyzed data sets and explains how they were developed, Section 4 describes the
types of inaccuracy users should expect in the damage estimates, Section 5 compares damage
estimates from different sources and analyzes the accuracy of the estimates, Section 6 suggests
ways of dealing with data omissions and inconsistencies, Section 7 provides guidance for use
and interpretation of the reanalyzed data, with examples and wamings, and concludes with
recommendations regarding future collection and dissemination of flood damage estimates,

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