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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Services (personal communication 2000).
(5) Wisconsin: One report on the 1993 Midwest flood summarizes flood losses in Wisconsin
from 1973 through 1992 (FEMA 1993), and another report provides loss estimates for the
1993 flood (Wisconsin Dept. of Natural Resources 1993).

In the state reports, the loss estimates are provided for each major flood event, sometimes
with two or more events occurring in a given year. To match the annual loss estimates provided
by NWS-IDC, we added up the flood losses in each state for each year, using calendar years
during 1955-1982 and fiscal years (Oct-Sep) during 1983-1998 to match the time periods used
in the NWS estimates.' Our comparison covers a total of 155 years in the 5 states: 44 years each
in California and Colorado (1955-1998), 24 years in Michigan (1975-1998), 22 years in
Virginia (1977-1998), and 21 years in Wisconsin (1973-1993).

Of course, the state estimates are subject to the same types of error as the NWS estimates
- neither is assumed a priori to be more accurate. The intent of this section is to investigate
large discrepancies between estimates from different sources in order to understand how
estimates of the same event vary and to determine whether some floods are overlooked. In the
following analysis, all loss estimates are reported in inflation-adjusted 1995 dollars.

When estimates are very low or missing
Table 5-2 provides a comparison of the estimates in all 155 years, with cases along the
diagonal (from upper-left to lower-right) showing the closest agreement. An obvious difference
between the NWS and state estimates is in the amount of missing data - a result of different
purposes of the data. NWS flood loss estimates are collected every year, with relatively small
losses included; hence, estimates are missing or zero in only 28 years and are below $5 million in
56 years. In contrast, the state reports focus on more serious floods, so years of relatively low
flood loss are not included. The states did not report losses in 91 cases, and included losses
below $5 million in only 6 cases.' The threshold for reporting appears to be somewhat higher in
California, where the lowest reported loss was $15 million.

We conclude that these five states do not attach great importance to floods that cause less
than $5 million in damage; therefore, annual losses below that threshold will be described as
"low" flood losses. Lumping the low and missing categories together, the NWS and states agree
that 78 (50%) of the 155 cases involved little or no flood damage. Disagreements arise,
however, when at least one estimate is above $5 million.

3Estimates for 1980-82 were included at this stage of the analysis. California flood damage in Dec 1982 could be
attributed differently by the two sources because of the overlap in definition of calendar year 1982 and fiscal year
1983. The other four states did not report losses in Oct-Dec 1982.

'During 1955-98, California reported losses in 26 years (59%), while Colorado repnrted losses in only 13 years
(30%). The other three states repnrted losses in 33-41 % of the years covered by their reports (8 years in Michigan, 9
years in Virginia, and 8 years in Wisconsin).

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