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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3. DEVELOPMENT OF THE DATA SETS

The national data obtained from NWS consisted of annual total damage estimates for the
D,S" including three territories: Puerto Rico (since 1975), the Virgin Islands (since mid-1980s),
and Guam (since 1994), The state data contained annual damage estimates for each state and, in
recent years, the three territories, In the national data, we subtracted estimates for the three
territories from the U,S, totals to create a more uniform time series representing only the 50
states.

NWS estimates were spot-checked against those from other agencies, Estimates that
appeared to be extremely large or small compared to published accounts of events were
examined especially closely, In inc1ividual events that received follow-up study by the DSACE,
more accurate estimates were sometimes available, However, except during 1976-1982, there
exists no compelling reason to change the NWS estimates or defer to another agency's estimates,
Section 5 provides a quantitative assessment of uncertainty in the estimates and the implications
for their effective use,

With a few important exceptions, the estimates presented as a result of this project have
their origins in published NWS data, Obvious clerical errors have been corrected (see
Section 4),

A. Resolving the Data Gap, 1976-1982
To compile a complete time series of annual estimates required finc1ing additional flood
damage estimates for the years 1976-1982, As explained in Section 2, NWS ceased publication
of annual flood damage summaries after 1975, Publication of comparable damage estimates c1id
not resume until 1983, when USACE reports made damage estimates available again at the state
and national levels, but not at the river basin level.

To make the state and national data sets as complete as possible, we focused on obtaining
and evaluating estimates for 1976 through 1982, The NWS website (NWS-HIC 2001) included
previously unpublished national flood damage estimates for 1976-1982, and an NWS
spreadsheet included unpublished state estimates for that period, However, the national
estimates and the state total estimates c1iffered by large margins, An old, undocumented NWS
computer printout tallied inc1ividual floods, by state, in the years 1976-1988, but we found it to
be filled with errors and inconsistencies,

Despite a curtailment of effort, the NWS continued to compile some damage estimates
during 1976-1979, which served as a starting point for our reconstruction attempts, We were
able to develop estimates for 1976-1979 based on information in the NWS files and reports from
other sources, as described in Appenc1ix A,

Although we tried to reconstruct estimates for 1980-1982, there were not enough sources
of information, either from NWS or other agency publications, to provide estimates for those
years comparable to the data in the overall data set. Furthermore, there were some large
disparities between estimates found in the NWS-HIC archives for the period 1980-1982 and
damage estimates provided by states, leading us to conclude that some of the damage estimates
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