Assessment of Flood Losses in the United States

Abstract

Private property insurance data on losses resulting from floods in the U.S. during 1972-2006 provide useful new measures of flood losses across the nation, as well as variations over this 35-year period, for floods labeled as catastrophes–531 events causing $1 million or more in losses. Assessment of the flood loss data reveals four types of damaging floods: hurricane-related floods, snow-melt floods, floods associated with major convective storms, and flood-only events. The regional aspects of flood events and their losses as well as temporal patterns were assessed. Planning for and responding to floods requires quality measures of losses created by past floods (Changnon 1999). Unfortunately, much of the flood loss data and information readily available have been based on estimates of losses. Quantified long-term loss data created by assessors who measured each damaged entity have not been available. Existing measures of flood losses include estimates of damages to facilities or crops plus information in news media reports and in government agency calculations of response costs. These sources collectively serve as an approximation of actual flood losses (Pielke 2000). Insurance loss data from the private sector is a more accurate measure of flood losses (National Research Council 1999), but it has not been accessible until provided for this study. The government-operated National Flood Insurance Program does not have long-term data and is not as extensive coverage as the private sector data. Since 1972, the property insurance industry has systematically collected data on major weather-caused loss events, ones they labeled as “catastrophes” (Property Claims Services 2007). These were losses of $1 million or more per event, and each listed the causative weather conditions such as floods, hail, tornadoes, heavy snow, icing, and hurricanes. The catastrophe loss data from 1972-2006 were used to analyze four types of damaging floods: events caused solely by floods; events caused by snow-melt floods; flood losses from hurricanes; and floods associated with major convective storms including those that also produced tornadoes, hail, and high winds. The values are based on losses to insured property, which includes vehicles, buildings, and other structures, and they represent 90 percent of all storm-produced property losses (Roth 1996, Changnon and Hewings 2001). This assessment addresses the magnitudes of flood losses, flood loss locations within the nation, and the temporal distributions of flood losses. Flood incidences and losses were assessed for each flood type and for all flood catastrophes.