A hydrological event is a vector of hydrological/meteorological variables corresponding to different variables and/or different time scales and locations. An event is unusual if it is on or near the boundary of the multivariate set corresponding to the series of events. Boundary and near boundary points can be identified using the half-space depth defined by Tukey. The relationship between unusual events and extremes on different scales is investigated. It is shown that all extremes are unusual events, but not all unusual events are extremes. Unusual events with respect to different time intervals are investigated to show climate evolution and to identify events which never occurred before and events which disappeared with time. Statistical significance of changes in the occurrence of unusual events can be assessed using Bootstrap methods. Hydrological series of river discharge and precipitation from South-West Germany are used to demonstrate the methodology.
Keywords: Multivariate extremes; Halfspace depth
Biography: Andras Bardossy is professor for hydrology and geohydrology at the University of Stuttgart. He studied Mathematics in Budapest and holds a doctoral degree both in mathematics (1981) and civil engineering (1993). His main interest is the stochastic modelling of precipitation in space and time and the space time interpolation of environmental variables. He published more then 100 papers in differenrt scientific journals.