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The 100-Year Flood Term Explained 

 January 25, 2023

By  Lora Keller

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For anyone who lives in Florida or plans to someday, the 100-year and 500-year flood are terms you need to know and understand. These terms refer to different areas of a floodplain and considering that basically all of Florida is a flood zone, this is crucial information to know.

These terms are easy to misunderstand or to misinterpret. Using the term “100-year flood” makes it sound like a flood is predicted to happen in the area once every 100 years. Of course, there’s no way that scientists can accurately predict something happening (such as a flood) 100 years in the future. That is a bit farfetched. 

The 100-year flood is a term referring to the probability of a flood happening in the area within the next 100 years. It is still completely possible for flooding to not occur at all within that 100 years or for that area to flood 2 or 3 times in 100 years. It is all about assessing the probability of a flood occurring.

The 100-Year Flood Explained

The probability of a flood happening in the 100-year flood zone is 1%. That means 1 time within 100 years is how often we should expect to see flooding.

Example:

If you are looking to buy a house in the 100-year flood zone, the property has a 1 in 100 (aka 1%) chance in any given year to experience a major flood. 

This might not sound like a significant amount, however, FEMA considers any area with a 1% chance of flooding a high-risk flood zone. Purchasing a property in a 100-year flood zone will require that you get flood insurance if your mortgage is federally backed. 

With about 50% of all mortgage loans in the United States being backed by some sort of government enterprise or another, you most likely will be required to get flood insurance. And for good reason. 

Living in a 100-year flood zone, you have over a 25% chance that you will experience a damaging flood over a standard 30-year mortgage loan. 

The 500-Year Flood Explained

The term 500-year flood refers to the probability of a flood happening one time in that area within the next 500 years which statistically is 0.2%. 

Example:

If you are looking to buy a house in an area that is in the 500-year flood zone, the property has a 1 in 500 (aka 0.2%) chance in any given year to experience a major flood.

So FEMA would consider this a moderate-risk zone. Living in a 500-year flood zone, you have a little over a 5% chance that you will experience a damaging flood over a standard 30-year mortgage loan. That is a significant jump down in comparison to the 100-year flood zone. 

FEMA does still recommend flood insurance for moderate-risk and even low-risk homes.

Lora Keller

CertResRD3931


Lora Keller 

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