The FORGEX method of rainfall growth estimation II: Description

摘要

The Focused Rainfall Growth Extension (FORGEX) method produces rainfallgrowth curves focused on a subject site. Focusing allows the incorporation ofrainfall extremes observed regionally while respecting local variations ingrowth rates. The starting point for the analysis is an extensive set of annualmaximum rainfalls, with values at each gauged site standardized by the median.Following the philosophy of the earlier FORGE method, a strongly empiricalapproach is adopted. The rainfall growth curve is represented by linear segmentson a Gumbel scale, and is fitted by a least-squares criterion. The selection ofdata points is intricate and includes both the traditional pooling of regionalextremes and the incorporation of network maximum events. The latter comprisethe largest events from successive hierarchical networks of gauges, focused onthe site for which estimates are requires. Their treatment takes account ofinterdependence using the Dales and Reed model of spatial dependence in rainfallextremes.