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2 I I I I I I I I I I I I I I I I I I I local level. Moreover, researchers need guidance to use the data effectively, Some data sets are not accurate enough for certain types of analysis, B. Sources of Historical Flood Damage Data Ideally, a national database of historical flood damage should cover the entire country over a long time period, using consistent criteria and methods in all times and places, Table 1- I compares possible sources of damage data. The National Weather Service is the only organization that has maintained a long-term and fairly comprehensive record of flood damage throughout the D,S. Insurance company records include only insured property, Records ofthe Federal Emergency Management Agency (FEMA) include only property that qualifies for federal assistance in presidentially declared disasters, Few state and local governments maintain damage records beyond those required by FEMA, Only in newspaper archives from cities and towns across the nation might one find more complete reporting of historical flood damage, Indeed, a newspaper archive could be the best source of information on flood damage in a particular locale, But the parochial nature of such data makes aggregation problematic, For long-term coverage of the entire nation, and of most states, the NWS data sets appear to be the best available source of flood damage estimates. However, the scope, accuracy and consistency of the data must be evaluated to determine how they can be appropriately used and interpreted, C. Scope of the NWS Flood Damage Data The NWS Hydrologic Information Center (NWS,mC 2001) describes the data as "loss estimates for significant flooding events," providing estimates of "direct damages due to flooding that results from rainfall and/or snowmelt." However, key concepts such as "flood" and "flood loss" are defined differently by various agencies and researchers depending on their objectives, Appropriate use of NWS damage data requires understanding of what is and is not included, Types of Flooding Ward (1990) defines a flood broadly as "a body of water which rises to overflow land which is not normally submerged," This definition covers river and coastal flooding, rainwater flooding on level surfaces and low-gradient slopes, flooding in shallow depressions which is caused by water-table rise, and flooding caused by the backing-up or overflow of artificial drainage systems, The NWS includes damage from most types of flooding listed above, but excludes ocean floods caused by severe wind (storm surge) or tectonic activity (tsunami), These are excluded because, although they result in water inundation, they are not hydrometeorological events, In addition, the NWS excludes damage that results from mudslides because, though they are caused by excess precipitation, they are considered primarily a geologic hazard,