Extreme value theory or extreme value analysis (EVA) is a branch of statistics dealing with the extreme deviations from the median of probability distributions. It seeks to assess, from a given ordered sample of a given random variable, the probability of events that are more extreme than any previously observed. Extreme value analysis is widely used in many disciplines, such as structural engineering, finance, economics, earth sciences, traffic prediction, and geological engineering. For example, EVA might be used in the field of hydrology to estimate the probability of an unusually large flooding event, such as the 100-year flood. Similarly, for the design of a breakwater, a coastal engineer would seek to estimate the 50 year wave and design the structure accordingly.
Extreme value theory is used to model the risk of extreme, rare events, such as the 1755 Lisbon earthquake.
A 100-year flood is a flood event that has on average a 1 in 100 chance of being equaled or exceeded in any given year.
Mississippi River at Kaskaskia, Illinois, during the Great Flood of 1993
High-water scale 1501–2002 at Passau, Germany, as of September 2012