Abstract
Abstract. The work aims at analyzing the bivariate relationship between flood peaks and flood volumes, with a particular focus on the type and seasonality of flood generation processes. Instead of the usual approach that deals with an analysis of the annual maxima of flood events, the current analysis includes all independent flood events in a catchment. Flood events are considered independent when they originate from distinguishably different synoptic/meteorological situations. The target region is located in the northern part of Austria, and consists of 72 small and mid-sized catchments. On the basis of the discharge measurements with a time resolution of 1 h from the period 1976–2007, independent flood events were identified and were assigned to one of the three following flood generation type categories: synoptic floods, flash floods and snowmelt floods. These were subsequently divided into two seasons, thereby separating predominantly rainfall-fed and snowmelt-fed floods. Nine frequently-used copula types were locally fitted to the samples of the flood type and seasonal data. Their goodness-of-fit was examined locally as well as analyzed in a regional scope. It was concluded that (i) treating flood processes separately is beneficial for the statistical analysis; (ii) suitability patterns of acceptable copula types are distinguishably different for the seasons/flood types considered, (iii) the Clayton and Joe copulas shows an unacceptable performance for all the seasons/flood types in the region; (iv) the rejection rate of the other copula types depends on the season/flood type and also on the sample size; (v) given that usually more than one statistically suitable dependence model exists, an uncertainty analysis of the design values in the engineering studies resulting from the choice of model seems unavoidable; (vi) reducing uncertainty in the choice of model could be attempted by a deeper hydrological analysis of the dependence structure between flood peaks and volumes in order to give hydrological support to the decision on model's suitability in specific regions and for typical flood generation mechanisms.
Highlights
The design of flood retention basins and other hydraulic structures where storage is involved requires the entire hydrograph or, at least, the flood volume/shape estimates related to the flood peaks
The copula types are organized alphabetically, while the catchments are organized according to their original catchment IDs
Most of the work done so far does not relate to the hydrological adequacy of the copula selection, e.g., by directing the multivariate analysis toward the selection of certain types of models for specific runoff generation processes
Summary
The design of flood retention basins and other hydraulic structures where storage is involved requires the entire hydrograph or, at least, the flood volume/shape estimates related to the flood peaks. The relationship between flood peaks and volumes is an interesting scientific research issue both from the statistical and hydrological points of view. The examination of the interplay of climatic and catchment processes in defining the probabilities of peaks and volumes is a challenging problem (Gaál et al, 2015). The statistical analysis of flood peaks and volumes are often dealt with in a multivariate frequency framework. The use of copula-based multivariate models have attracted a lot of attention. Their advantage is that they permit to separate study of the marginal distributions of the components and the de-
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