A 100-year flood, also called a 1% flood, or High Probability in the UK, is a flood event for a defined location at a level reached or exceeded once per hundred years, on average, but as there are many locations there are multiple independent 100-year floods within the same year. In the US, it is estimated on past records as having a 1 in 100 chance (1% probability) of being equaled or exceeded in any given year.
A 100-year flood, also called a 1% flood, or High Probability in the UK, is a flood event for a defined location at a level reached or exceeded once per hundred years, on average, but as there are many locations there are multiple independent 100-year floods within the same year. In the US, it is estimated on past records as having a 1 in 100 chance (1% probability) of being equaled or exceeded in any given year.
Source: Wikipedia "100-year flood" · CC BY-SA 4.0
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