Regional rainfall depth-duration-frequency equations for an alpine region

In this paper the scaling hypotheses are applied to annual maximum series of rainfall depth for different rainfall duration to derive the depth–duration–frequency (DDF) curve. It is shown that, based on the empirically observed scaling properties of rainfall and some general assumptions about the cumulative distribution function for the annual maxi- mum of the rainfall depth, it is possible to derive a simple DDF relationship. This general framework provides a basis for the generation of maps that can be used to infer DDF curves at any point of a particular area. Data from a dense raingauge network in a mountainous region in north-eastern Italy (the Trentino Province) are used to clarify the methodology for the construction and regionalization of the DDF relationship. The geographical variation of short-duration (i.e., less than 60 min) rainfall extremes is also evaluated by using the same framework. It is found that depth–duration ratios, defined as the ratios of the t-min to the 60- min rainfall depths of the same return period, may be considered independent of return period and geographical location for any storm duration less than 60 min.