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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1. INTRODUCTION

A. Why We Need Historical Flood Damage Data
The National Weather Service (NWS) estimates that flooding caused approximately $50
billion damage in the U,S, in the I990s (NWS-IDC 2001), Although flood damage fluctuates
greatly from year to year, estimates indicate that there has been an increasing trend over the past
century (Pielke and Downton 2000), Some have speculated that the trend is indicative of a
change in climate (e,g" Hamburger 1997), some blame population growth and development (e,g,
Kerwin and Verrengia 1997), others place the blame on federal policies (e,g" Coyle 1993), and
still others suggest that the trend distracts from the larger success of the nation's flood policies
(e,g, Labaton 1993),

To understand increasing damage and assess implications for policy, decision makers
need to resolve the independent and interdependent influences of climate, population growth and
development, and policy on trends in damage. Increased flood damage due to changing climate
requires different policy actions than would damage increases due to implementation of flood
policies,

The available records of historical flood damage are inadequate for policy evaluation,
scientific analysis, and disaster mitigation planning, There are no uniform guidelines for
estimating flood losses, and there is no central clearinghouse to collect, evaluate, and report
flood damage, The data that exist are rough approximations, compiled by the NWS from
damage estimates that are reported in many different ways. Moreover, most published
summaries of the damage estimates focus primarily on aggregate national damage totals,

Scientists need historical flood damage data at a variety of spatial scales to analyze
variations in flood damage and what contributes to them, For example, during El Nino years,
southern California receives more precipitation than in the typical year, Conventional wisdom
suggests that the increase in precipitation should result in an increase in damaging floods, If
California's emergency planners knew this to be the case, they could prepare for the floods that
come with El Nino, possibly reducing damage, In this case, scientists looking for a causal
relationship would want to determine to what degree historical high damage years in southern
California are associated with EI Nino events. This requires sub-state-level data sets, rather than
a national data set.

Social scientists looking at the effect of policies designed to reduce flood damage also
need access to historical data at regional and local scales, Take the example of the National
Flood Insurance Program, created in 1968 to "assist in reducing damage caused by floods" (42
U,S,C, ~ 4102 (c)(3)), Researchers evaluating the program would like to isolate the effect of the
program from all other factors influencing flood damage in particular areas, At the river basin or
community level, the effect of a federal policy implemented in 1968 might be isolated and
measured,

In sum, historical damage data are essential for any study that seeks to understand the
role that climate, population growth and development, and policy play in determining trends in
flood damage, Some studies might require data at the national level, and others at the state or

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