The Federal Emergency Management Agency (FEMA) has placed nearly 20,000 communities in the United States into categories of flood zones. Every community is able to participate in the agency's National Flood Insurance Program (NFIP), which administers flood insurance policies for homeowners, renters and business owners. Premium rates determined by the risks of flooding. If you live in a higher-risk area, your mortgage lender may require you to hold flood insurance

The NFIP is also in charge of mapping flood zones, which are depicted on a community's Flood Hazard Boundary Map or a Flood Insurance Rate Map (FIRM). If you'd like to know the flood risk for your property, the easiest way is to visit the NFIP's online database on flood risk and input your address. If you're a homeowner in a floodplain, it's not so much a question of if a flood will damage your property as when.

Know your zone

To indicate the risks in different parts of the country, FEMA has assigned a letter of the alphabet to each zone. Below are FEMA's zone definitions.

Moderate to low risk: Zones B, C, and X

In communities that participate in the NFIP, flood insurance is available to all property owners and renters with moderate to low risk.

These are areas outside the 1-percent annual chance floodplain, areas of 1 percent annual chance of sheet-flow flooding where average depths are less than 1 foot, areas of 1 percent annual chance stream flooding where the contributing drainage area is less than 1 square mile, or areas protected from the 1 percent annual chance flood by levees. Flood insursance is not required in these zones.

High risk: The As

In communities that participate in the NFIP, mandatory flood insurance purchase requirements apply to all A zones.

Zone AE and A1-A30: Areas with a 1 percent annual chance of flooding and a 26 percent chance of flooding over the life of a 30-year mortgage.

Zone AH: Areas with a 1 percent annual chance of shallow flooding, usually in the form of a pond, with an average depth ranging from 1 to 3 feet. These areas have a 26 percent chance of flooding over the life of a 30-year mortgage.

Zone AO: River or stream flood hazard areas and areas with a 1 percent or greater chance of shallow flooding each year, usually in the form of sheet flow, with an average depth ranging from 1 to 3 feet. These areas have a 26 percent chance of flooding over the life of a 30-year mortgage. Average flood depths derived from detailed analyses are shown within these zones.

Zone AR: Areas with a temporarily increased flood risk due to the building or restoration of a flood-control system (such as a levee or a dam). Mandatory flood insurance purchase requirements will apply, but rates will not exceed the rates for unnumbered A zones if the structure is built or restored in compliance with Zone AR floodplain management regulations.

Zone A99: Areas with a 1 percent annual chance of flooding that will be protected by a Federal flood-control system where construction has reached specified legal requirements.

High risk coastal: The Vs

In communities that participate in the NFIP, mandatory flood insurance purchase requirements apply to all V zones.

Zone VE and V1 - 30: Coastal areas with a 1 percent or greater chance of flooding and an additional hazard associated with storm waves. These areas have a 26 percent chance of flooding over the life of a 30-year mortgage. Base flood elevations derived from detailed analyses are shown at selected intervals within these zones.

Undetermined: D