The term 100-year flood has been tossed around a lot in recent weeks. However, its meaning is a bit misleading. Here is what you need to know about this term and what it actually means.
Understanding the Meaning of a 100-Year Flood
With so many flash flooding events happening across the U.S. this summer, meteorologists have been using the term "100-year flood" quite frequently. The term is used to designate a flooding event that only has a 1% chance of happening over the course of a year at any specific location based on historical averages. The U.S. Geological Survey (USGS) notes that the term was developed in the 1960s as a tool to measure a flood's severity for the National Flood Insurance Program.
While there is only a 1% chance of a 100-year flood happening in any given year, it does not mean that if an area experienced this anomaly last year, it is in the clear for a while. The recent flooding in central Texas along the Guadalupe River is a perfect example of this. Just one year after the deadly flooding disaster that killed over 100 people on July 4, 2025, the same general region of Texas Hill Country saw a similar event unfold just a few weeks ago.
The community of Comfort, Texas, notched flood crests in 2025 and 2026 that came in as two of the top five highest on record. These records date back to 1869, speaking to the rarity of the rainfall of this magnitude.
The situations in central Texas are not the only examples of historic 100-year flood events that have happened in a short time frame. Hurricane Harvey brought torrential rainfall to Houston and the rest of southeastern Texas in August 2017. This was the region's third 500-year flood event in three years, coming on the heels of the Memorial Day 2015 disaster and the Tax Day floods of 2016,
Moving out of Texas, Ellicott City, Maryland, also experienced two disastrous floods in a period of less than two years. The first event happened on July 30, 2016, followed by another similar natural disaster on May 27, 2018.
What is to blame for the increasing volume of 100-year floods? Climatologists say that global warming is driving the threat of heavy rain capable of producing flooding with more regularity. According to a study from Climate Central, 90% of the U.S. cities examined have notched heavier rainfall rates in 2026 than in 1970. This is because warmer air is able to pack higher volumes of moisture, amplifying rainfall totals.
It stands to reason that times of heavy rain are more likely to trigger flash flood events. Meteorologists warn that the increasing influence of climate change will continue to fuel higher chances of a 100-year flood hitting your community, not just once but several times in your lifetime.
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