Abstract:Building on the work of Bedford, Cooke and Joe, we show how multivariate data, which exhibit complex patterns of dependence in the tails, can be modelled using a cascade of pair-copulae, acting on two variables at a time. We use the pair-copula decomposition of a general multivariate distribution and propose a method for performing inference. The model construction is hierarchical in nature, the various levels corresponding to the incorporation of more variables in the conditioning sets, using pair-copulae as … Show more
“…Another possibility to construct copula models of higher dimensions is the use of pair-copulas (Joe, 1996;Aas et al, 2009). They are based on conditional bivariate copulas, which can be coupled by the concept of vines (Bedford and Cooke, 2002).…”
Section: Estimation Of Multivariate Return Periods Via 3-dand Pair-comentioning
Abstract. Although the consequences of floods are strongly related to their peak discharges, a statistical classification of flood events that only depends on these peaks may not be sufficient for flood risk assessments. In many cases, the flood risk depends on a number of event characteristics. In case of an extreme flood, the whole river basin may be affected instead of a single watershed, and there will be superposition of peak discharges from adjoining catchments. These peaks differ in size and timing according to the spatial distribution of precipitation and watershed-specific processes of flood formation. Thus, the spatial characteristics of flood events should be considered as stochastic processes. Hence, there is a need for a multivariate statistical approach that represents the spatial interdependencies between floods from different watersheds and their coincidences. This paper addresses the question how these spatial interdependencies can be quantified. Each flood event is not only assessed with regard to its local conditions but also according to its spatio-temporal pattern within the river basin. In this paper we characterise the coincidence of floods by trivariate Joe-copula and pair-copulas. Their ability to link the marginal distributions of the variates while maintaining their dependence structure characterizes them as an adequate method. The results indicate that the trivariate copula model is able to represent the multivariate probabilities of the occurrence of simultaneous flood peaks well. It is suggested that the approach of this paper is very useful for the risk-based design of retention basins as it accounts for the complex spatio-temporal interactions of floods.
“…Another possibility to construct copula models of higher dimensions is the use of pair-copulas (Joe, 1996;Aas et al, 2009). They are based on conditional bivariate copulas, which can be coupled by the concept of vines (Bedford and Cooke, 2002).…”
Section: Estimation Of Multivariate Return Periods Via 3-dand Pair-comentioning
Abstract. Although the consequences of floods are strongly related to their peak discharges, a statistical classification of flood events that only depends on these peaks may not be sufficient for flood risk assessments. In many cases, the flood risk depends on a number of event characteristics. In case of an extreme flood, the whole river basin may be affected instead of a single watershed, and there will be superposition of peak discharges from adjoining catchments. These peaks differ in size and timing according to the spatial distribution of precipitation and watershed-specific processes of flood formation. Thus, the spatial characteristics of flood events should be considered as stochastic processes. Hence, there is a need for a multivariate statistical approach that represents the spatial interdependencies between floods from different watersheds and their coincidences. This paper addresses the question how these spatial interdependencies can be quantified. Each flood event is not only assessed with regard to its local conditions but also according to its spatio-temporal pattern within the river basin. In this paper we characterise the coincidence of floods by trivariate Joe-copula and pair-copulas. Their ability to link the marginal distributions of the variates while maintaining their dependence structure characterizes them as an adequate method. The results indicate that the trivariate copula model is able to represent the multivariate probabilities of the occurrence of simultaneous flood peaks well. It is suggested that the approach of this paper is very useful for the risk-based design of retention basins as it accounts for the complex spatio-temporal interactions of floods.
“…Aas et al [29] illustrate a first application of the vine copulas applying non-Gaussian pair copulas to financial data. Apart from many applications to financial data like [30], pair-copula constructions are used in areas as diverse as hydrology, medicine or genetic and evolutionary computation, see [31][32][33], respectively.…”
Section: A Short Primer On Pair-copulas Including Specification and Ementioning
confidence: 99%
“…Consequently, very complex and asymmetric dependence structures can be modeled. The specific definition of pair-copulas leads to three fundamental estimation and selection tasks (see e.g., [35]): firstly, estimation of copula parameters for a chosen vine tree structure and pair copula families (for details on estimation of vine copulas like SSP or ML (maximum likelihood) estimation, we refer to [29,[36][37][38] or [39]); secondly, selection of the parametric copula family for each pair copula term and estimation of the corresponding parameters for a chosen vine tree structure; and, thirdly, selection and estimation of all three model components.…”
Section: A Short Primer On Pair-copulas Including Specification and Ementioning
Abstract:In this paper, we demonstrate the superiority of vine copulas over conventional copulas when modeling the dependence structure of a credit portfolio. We show statistical and economic implications of replacing conventional copulas by vine copulas for a subportfolio of the Euro Stoxx 50 and the S&P 500 companies, respectively. Our study includes D-vines and R-vines where the bivariate building blocks are chosen from the Gaussian, the t and the Clayton family. Our findings are (i) the conventional Gauss copula is deficient in modeling the dependence structure of a credit portfolio and economic capital is seriously underestimated; (ii) D-vine structures offer a better statistical fit to the data than classical copulas, but underestimate economic capital compared to R-vines; (iii) when mixing different copula families in an R-vine structure, the best statistical fit to the data can be achieved which corresponds to the most reliable estimate for economic capital.
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