Abstract
Abstract. This study aims to better understand the effect of catchment scale and climate on the statistical properties of regional flood frequency distributions. A database of L-moment ratios of annual maximum series (AMS) of peak discharges from Austria, Italy and Slovakia, involving a total of 813 catchments with more than 25 yr of record length is presented, together with mean annual precipitation (MAP) and basin area as catchment descriptors surrogates of climate and scale controls. A purely data-based investigation performed on the database shows that the generalized extreme value (GEV) distribution provides a better representation of the averaged sample L-moment ratios compared to the other distributions considered, for catchments with medium to higher values of MAP independently of catchment area, while the three-parameter lognormal distribution is probably a more appropriate choice for drier (lower MAP) intermediate-sized catchments, which presented higher skewness values. Sample L-moment ratios do not follow systematically any of the theoretical two-parameter distributions. In particular, the averaged values of L-coefficient of skewness (L-Cs) are always larger than Gumbel's fixed L-Cs. The results presented in this paper contribute to the progress in defining a set of "process-driven" pan-European flood frequency distributions and to assess possible effects of environmental change on its properties.
Highlights
The companion paper by Salinas et al (2014) presents a newly established database of flood L-moments from 13 European countries
On the basis of these considerations, this paper addresses the two main scientific questions: can we quantify the main physical controls on the shape of the flood frequency distribution at a regional scale? Can we represent these controls graphically on L-moment ratio diagrams to guide the selection of suitable parent distribution on the basis of fundamental catchment descriptors? For this purpose, a subset of the data presented in Salinas et al (2014) with a total of 1132 catchments from Austria, Italy, and Slovakia is used to study the control of commonly available physiographic and climatic characteristics on the properties of the underlying probability distribution of flood flow
To minimize the possible effects of sampling variability associated with short records when estimating higher-order sample L-moments, the minimum record length was set to 25 yr of data, reducing the data set to a total of 813 catchments (Austria, 493 gauges; Italy, 151 gauges; and Slovakia, 169 gauges)
Summary
The companion paper by Salinas et al (2014) presents a newly established database of flood L-moments from 13 European countries. Monte Carlo simulations showed that there is not enough statistical evidence for the existence of a single three-parameter distribution suitable for representing flood frequency regimes all over Europe. This supports the fact of statistical model selection being a topical issue in hydrology and flood frequency analysis in particular (see e.g. Laio et al, 2009). Concerning probabilistic model selection, Hosking and Wallis (1997), Vogel and Fennessey (1993) and Peel et al (2001), among others, recommend using the L-moment ratio diagrams to guide the selection of the most suitable parent flood frequency distribution.
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