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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For determining the frequency of damaging floods, we recommend establishing a threshold
above which damage estimates are expected to be provided consistently. In our analysis we have
chosen to use the frequency of inflation-adjusted state flood damage estimates above $1 million.

B. Magnitude of Damages
Individual states differ greatly, both in flood frequency and in the magnitude of damage in
a "typical" flood event. Figure 6-2 shows, for each state, the estimated total damage during the
years 1955-1978 and 1983-1999, as well as the damage in the worst flood year. A few states
have had many major floods (e.g. California, Texas). Many others have suffered most of their
total damage in just one or two major flood events (including Pennsylvania and Iowa, among the
worst in total damage). Many states had no yearly damage greater than $500 million in this
period, and there are 10 states whose total dalllage for the entire 41-year period is less than $500
million.

These state comparisons do not include 1979 damage estimates because some estimates for
that year are available only for large regions, not for individual states (see Section 3). Estimates
of 1979 damage are available for many states, however, and are useful to illustrate how rankings
of states by total damage can differ depending on the time period covered. For example, 1979
flood damage in Texas was $3.76 billion - substantially greater than in any of the years
included in Figure 6-2. Texas would move from 6'b to 3rd place in the rankings if 1979 were
included.

The frequency distributions of flood damage in each state give another perspective on past
flood vulnerability. Table 6-1 shows how states differ in both frequency and severity of
damaging floods during 1955-1978 and 1983-1999. The states are ordered by their median
annual flood damage based on all 41 years, including years with no reported damage. The
number of missing, very low (< $1 million) and relatively high (> $100 million) damage
estimates are shown to indicate both frequency and relative magnitudes of flood damage. Three
"historical vulnerability categories" can be loosely defined to illustrate the differences between
states. (Although the worst flood, indicated by maximum damage, is shown for each state, it is
not considered in defining historical categories.)

(1) Low vulnerability: Floods are relatively infrequent, and damage is less than about $2
million in the majority of years (1995$). Includes New England states, some mid-Atlantic
coastal states, low-population states in the arid west, plus Hawaii and Alaska. Damage rarely
exceeds $100 million. (Frequency distributions of flood damage in Maine and New Mexico are
surprisingly similar, despite their geographic differences.)

(2) Medium vulnerability: Damaging floods occur in most years, and median damage is in
approximately the $2 - 8 million range (1995$). Includes most states in the southeast, the lower
Mississippi basin, and the Pacific northwest. Most of these states have few instances of flood
damage over $100 million. (Louisiana is a notable exception.)

(3) High vulnerability: Damaging floods occur in most years, and damage exceeds about
$8 million in the majority of years (1995$). Includes states in the upper Mississippi, Missouri,

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