Average Recurrence Interval of Rainfall in Real-time

摘要

As society and infrastructure become increasingly more vulnerable and impacted by extreme rainfall events, the requirement for timely, accurate and informative rainfall information is paramount to protecting property, saving lives and efficiently managing water. Accurate rainfall data is becoming increasingly available, but translating it into meaningful information to support decisions is lacking. To make rainfall data more meaningful, an innovative technique for translating near real-time rainfall maps into "return period" maps has been created so users have an objective, timely, and accurate depiction of recent rainfall. Knowing how much rainfall fell at a particular location during a certain amount of time is useful, but expressing the rarity of rainfall in terms of a "return period" provides an objective and useful perspective of the rainfall. ARI maps of rainfall provide information that is analogous to the 100-year flood, but for rainfall instead.The use of the term "return period" has been criticized for leading to confusion in the minds of decision makers and the public, therefore to clarify the meaning and to be consistent with NOAA's National Weather Service Hydrometeorological Design Studies Center (HDSC), the term average recurrence interval (ARI) is used. For those who prefer a probability, an ARI can be easily converted into a probability. The ARI is the average number of years between exceedances of a given rainfall depth for a given duration at a specific point location.Historically, calculating the ARI of a given rainfall event has been inefficient, generalized for an area based on a single observation and/or lacking reliable underlying data. New methodologies address each of these. In a highly computational GIS environment, real-time ARIs are computed based gauge-corrected radar-estimated rainfall maps/grids from the National Weather Service (NWS) and Weather Decision Technologies, Inc. (WDT) together with official rainfall frequency grids/maps published by HDSC. Although the ARI of rainfall does not necessarily equate to a flood of the same ARI, the ARI of rainfall is an excellent indicator of flooding potential.