Devastating storms, severe flood, acute famine conditions, etc. hydrological events of extreme nature has changed human history. Any event which is not normal is known as an abnormal event. In the case of hydrology, an event that has a return period of more than 100 years is considered Extreme.
According to Herring(2020) of Climate.gov, "An extreme event is a time and place in which weather, climate, or environmental conditions—such as temperature, precipitation, drought, or flooding—rank above a threshold value near the upper or lower ends of the range of historical measurements."
Though the threshold is not objective, few researchers have defined "extreme events as those that occur in the highest or lowest 5% or 10% of historical measurements". Some have described events by their deviation from the mean, or by their occurrence interval.
Here the most severe five extreme hydrologic events were discussed which has changed the pathway of human history after the occurrence of these events. The impact of such events was experienced many decades after the event has occurred.
How have I selected the events?
At the time of selection, we have considered the death toll due to the event, return period, and impact on the future generation as the criteria. The decision-making tool "ODM" was used to find and sort the events as per their severity and placed them below:
