Analysis of Seasonal, Climate, and Elevation Effects on Times Between Storms

Storms? often need to be identified in a set of historic data for engineering uses, such as intensity-duration-frequency analysis, rainfall-erosivity factors for erosion estimation, structure design, and other uses. Often a storm is identified by assigning a fixed dry time between bursts of rainfall for the entire record. However, it is known that this dry time between storms varies seasonally, and it also does not necessarily produce storm events that are statistically independent. This study examines the use of a method to identify storms that accounts for season of year, climate, and topography. The minimum dry time between storms (critical dry-period duration) for arid, semiarid, and humid locations, and for mountainous terrain, and by season of year are determined by using an exponential distribution. The small-area spatial variability of critical duration (CD) within a climate is investigated, as well as the variation of CD with elevation at one site. Long records of short-time increment data (of the order of minutes) are scanty across the US. Consequently, relationships between CD and average monthly precipitation are evaluated for parameterizing the exponential distribution. The study has utility for drought preparedness and mitigation studies, risk analyses for agricultural crops and animals, stochastic simulation of rainfall events, etc.