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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5. ACCURACY OF DAMAGE ESTIMATES

In general, estimates of damage contain a high degree of uncertainty. Ideally, estimation
errors would be measured by systematically comparing estimates with actual costs, which often
are not known until long after a flood event. Unfortunately, actual cost data are seldom collected
in a form that can be compared with estimates made at the time of the flood. This section
examines the accuracy of flood damage estimates in two ways: (1) by comparing estimates with
actual costs in one large flood disaster, and (2) by comparing pairs of estimates from different
sources for many flood events.

A. Errors in Early Damage Estimates
NWS flood damage estimates are usually compiled within three months after a flood
event, long before the actual costs can be known. Until recently, even in serious disasters, actual
total damage costs were not systematically compiled by any agency. There was no way of
checking the accuracy, or even the reasonableness, of most damage estimates.

In recent years, however, FEMA has systematically collected cost data for the programs
it administers - admittedly only a fraction of total disaster costs. Beginning in 1992, FEMA
instituted a computerized system for recording and tracking applications for federal assistance in
presidentially declared disasters. State and county governments have gradually developed the
capabilities to link to this system. The damage estimates submitted by local officials to FEMA
probably represent the best available early estimates under disaster conditions. A team visits
each damage site to view the extent of losses and make preliminary estimates. Thus, in some
disasters and some jurisdictions, it is now possible to systematically compare early damage
estimates with actual costs. Data from FEMA's Public Assistance Program are particularly
appropriate for our purposes because a large portion of the losses involve physical damage to
property. Public assistance covers damage to public facilities such as roads and bridges, schools,
government buildings, and nonprofit agencies.

In the aftermath of a natural disaster, damage information is assembled according to
guidelines established by FEMA. The following stages are described by FEMA (1998) and
Michael Sabbaghian' of the California Office of Emergency Services (OBS) (personal
communication 8/30/00).

(1) Initial Damage Estimate (IDE): Local officials provide estimates of physical damage
based on early reports and descriptions, without necessarily visiting the damage sites.
(2) Preliminary Damage Assessment (PDA): A team including local, state, and FEMA
officials visits the damage sites to do a "windshield estimate," perhaps viewing the sites
from a car window or walking around. The PDA estimates are used to decide whether
federal assistance is needed. If so, they are submitted to FEMA as part of the govemor's
request for a presidential disaster declaration.

'Michael Sabbaghian, Deputy Public Assistance Officer for the California OES, manages disaster recovery activities
for infrastructure and is responsible for grant management. He explained the process for estimating and recording
losses in presidentially declared disasters. He also provided the damage estimates and cost data for the 1998
California EI Nino disaster, which is used in this section.