By now, given Mother Nature’s wrath over the past year, you’ve no doubt heard plenty of references to 100-year flood events, 500-year flood events and 1,000-year flood events. The description of flooding by the likelihood of occurrence in a geographic area is a predictive measure, commonly used by those in the scientific, emergency management and insurance industries. So what’s in a name? For property owners, an abundance of misunderstanding and a false sense of security. One need not look any further than the 2015 storm event that dumped more than 12 inches of rain across the state of South Carolina, impacting thousands of residential and commercial property owners.
In the editorial, Does a 1,000-year Storm Really Happen Every 1,000 Years, the LA Times puts together an excellent primer on the terminology of flooding events. Here are a few excerpts:
Technically the measurement is a probability. A 100-year flood means that there is one chance in 100 of a flood occurring in each year. A 500-year flood means there is 0.2% chance of the flooding or rain event occurring each year and a 1,000-year event has a 0.1% chance of happening in any year.
The computation of the probability starts with data collected by gauges that measure rainfall or the flow of streams, explained Jayme Laber, a hydrologist with the Los Angeles office of the National Oceanic and Atmospheric Administration.
The gauges collect “tons of data” over years that can then be sorted into a variety of categories. Rain gauges collect water as it falls; flood or stream gauges collect data as the water flows past.
Using software, the data are then sorted to allow the meteorologist to determine what is typical rainfall in a five-minute burst, or in an one-hour period or any other duration, Laber said.
From those data, meteorologists then extrapolate the probability of a rainfall or flooding event and express it as a number: once in 50 years, 100 years and so on.
The naming of flood events and designation of flood zones are used to determine a geographic region’s exposure to flooding. For a property’s actual assessment of exposure, there is no substitute for a flood risk evaluation, a comprehensive study of a structure’s individual characteristics. It is a proactive measure that will determine whether the cost of flood coverage is justified and will protect your real estate investment from a false sense of security.
Contact AmeriFlood Solutions, Inc. (AFSI) for more information. Ask about AFSI’s complimentary flood risk evaluation performed by an expert team of flood risk professionals.