A Classification Index for Precipitation Events in Maricopa County, Arizona

This paper outlines the work to develop an indexing method that describes the severity of multiple storm types (thunderstorms, general winter storms, tropical storms), that uses three storm parameters as inputs (areal average rainfall, storm duration, and storm or watershed area) and gives similar results for storms with similar rainfall/duration properties regardless of the area covered. A note – “severity” only applies to precipitation as a meteorological event – runoff (flooding) generated and damage caused are determined by an additional set of inputs. A decision was made at the outset to emulate the rating of the Richter Scale as used for earthquakes –where a 5 is noticed but does little damage, a 7 causes significant damage and a 9 is catastrophic and rarely experienced. The method’s application ranges from historic storms above stream measurement points, to comparisons over given geographic areas, to forecasting using QPF values inputs. It is easy for someone with a science background to use, gives nearly identical results no matter the qualified user, and is somewhat automated using commonly available software.