Hurricane Return Periods

Abstract

Abstract The occurrence of a hurricane is a rare event. The likelihood of rare events that are not periodic in time are expressed in terms of return periods. Return periods are used to describe the occurrence of earthquakes and extreme flood events. The qualification that events are not periodic is important. A phenomenon that occurs regularly-even if it is rare-is best described in terms of periodicities (see Chapter 10). Return periods are appropriately used when no important oscillations occur in the record. Various definitions for return periods lead to a vagueness concerning concepts associated with their use. For present purposes, both return periods and recurrence intervals are utilized. A recurrence interval is the time between successive events. The recurrence interval is also called the interarrival time. Recurrence intervals may vary widely and nonuniformly over the period of record. A return period is defined as the inverse of the annual probability. A hurricane which has a probability of once in 10 years is referred to as a 10-year event. A return period of 10 years should not be understood as a forecast of an event happening about every 10 years.1 Instead, over a long period of record, say 150 years, fifteen hurricanes can be expected to have occurred. Or, in any year, there is a 10% chance that a hurricane will occur. Unfortunately, there is no universally agreed upon definition of return period. The average of the recurrence intervals in the record serves as a rough estimate of the return period.