Thousands of Massachusetts property owners are discovering their homes and businesses are in newly designated federal flood zones, forcing them to buy additional insurance coverage that can easily exceed $2,000 annually.

The changes are the result of a Federal Emergency Management Agency project to remap flood zones, county by county nationwide. The agency plans to finish most of its Massachusetts maps by next summer, and local governments are in the process of notifying residents and business owners about the new zoning. At the same time, lenders are telling affected borrowers they must increase their insurance coverage.

Property owners across the state, confused and upset about the zoning changes, are calling local officials to complain and seek more information. FEMA designates a property as being in a flood area if historical data show it has a 1 percent or greater chance of flooding during any given year.

Michael Nakagawa, whose home is one of about 125 in Cambridge's Alewife section recently included in a flood plain, is organizing neighbors to challenge the new zoning.

"We shouldn't be forced to pay higher insurance rates and face lower property values because of the inaccuracies of their study,'' said Nakagawa, who lives near Alewife Brook. He hopes a surveyor can prove his home is safe from flooding because it is protected by an elevated sidewalk.

Catherine Daly Woodbury, storm water coordinator for the City of Cambridge, is sympathetic to the predicament of property owners, but just because a property hasn't been under water before does not mean it can't one day be flooded, she said.

"People are angry, and I try to point them in the right direction about where to get information for insurance and what their options are,'' Woodbury said. "Flood insurance is very expensive.''

FEMA's effort to replace decades-old paper maps with digital versions started six years ago, said David Mendelsohn, who is coordinating the agency's map modernization efforts in New England. Researchers are using new computer models and current topographical data to update maps drafted 20 or 30 years ago. As a result of improved technology, he said, areas susceptible to flooding at least once in a century can now be more precisely identified.

In addition, increased commercial and residential development is causing existing flood zones to be expanded, Mendelsohn said. Surfaces such as sidewalks and roadways can add to the risk of flooding during storms because they accelerate the flow of water.

FEMA defines a flood as a "condition where two or more acres of normally dry land or two more properties are inundated by water or mudflow.'' The agency does not specify water levels.