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For many areas the Federal Emergency Management Agency’s Flood Insurance Rate Maps (FIRMS) overestimate the amount of land area within the 100-year floodplain. New research suggests a way to improve the maps. The new three-pronged approach combines a new numerical computer model with two additional methods, satellite-image analysis and field observations. Each method serves as a check on the other two. The research team focused on the floodplains for a 10-year flood, a 100-year flood and a maximum flood for two sites in Arizona.

In addition to providing better hazard information to the public, revising the floodplains maps could have major economic impact in the rapidly growing Southwest. Often, homeowners in areas deemed to be in a floodplain must buy flood insurance in addition to regular homeowner’s insurance. The combined method applies to the foothills of western mountain ranges such as the Santa Catalinas and the Tortolitas outside Tucson. Many western cities, including Phoenix, Las Vegas and Denver, have similar foothills.
The research was supported by the National Science Foundation, the Pima County Flood Control District, the Arizona Geological Survey and the Flood Control District of Maricopa County.