It means that the event has been around for 100 years
A 100-year storm refers to a weather event that has a 1% chance of occurring in any given year based on historical data. It does not mean that the event will occur only once every 100 years. The term is used by engineers and planners to design structures to withstand extreme weather conditions.
The event will 100% occur.
An event of some sort that happens twice a year.
If an event keeps on occurring that means the event is at least annual. If it occurs more than once a year that makes the event perennial or biannual if it only occurs twice.
Do you mean a 9 year old? 100.
A 100-year flood is a flood of a given size for a particular area that has a 1% chance of happening in any given year. On average such an event will happen once per century. Remember, though, that this is merely an average; it is entirely possible for two 100-year floods to happen within a year of each other or for none to happen for thousands of years.
Then it is a certainty that the event is 100% to happen.
100%
An event that will definitely happen is an event with 100% probability.
Perhaps you mean anniversary, a celebration that happens once a year to commemorate a specific event.
Yes, a 100-year flood is more catastrophic than a 50-year flood. The term "100-year flood" refers to a flood event that has a 1% chance of occurring in any given year, while a "50-year flood" has a 2% chance of occurring in any given year. Therefore, a 100-year flood is rarer and typically results in more severe consequences in terms of damage and impact than a 50-year flood.
A probability of 0.1 means that there is a 10% chance of a particular event occurring. This indicates that out of 100 identical trials, you would expect the event to happen about 10 times on average. In other words, the likelihood of the event is relatively low.