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Regional maximum rainfall intensity-duration frequency (IDF)
curvesor formula have been widely used for estimating the design
rainfall atungauged sites. This study used 1~24 hours rainfall
annual maximumseries, which collected from 38 recording
raingauges over northernTaiwan, to develop regional IDF formula.
Before that, the frequencyanalysis at site was first studied.
Historical recorded data was applied tocompare the performance
of traditional parametric methods andnonparametric frequency
analysis, which utilized Gauss distribution asKernel function
and the least square cross validation method to
calculatesmoothing factor. The comparisons show that the
nonparametricfrequency has better performance based on Chi-
square test, KS test andRMSE as criteria. Moreover, the
comparison was further investigated interms of Monte Carlo and
Resampling simulation techniques. The resultsimply that
nonparametric frequency analysis have less variation for
largereturn periods when the sample is relative small.This study
further developed regional IDF based on the analysis
ofnonparametric frequency analysis. The station-year method was
applied topool nondimension rainfall intensity data in a
homogeneous region, whichwas classified by Yu and Chen (1996).
The average of daily annualmaximum rainfall was found to be
suitable chosen as an index in regionalIDF formula. The
simulation results show that the regional IDF formulahas less
than 20% absolution error. The vertifiation results from
sevenstations further concluded that the formulas can be
reasonably applied tothe non-recording raingauges or ungauges
sites.
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