Abstract
Flood generation is triggered by the interaction of the hydrological pre-conditions and the meteorological conditions at different space–time scales. This interaction results in floods of diverse characteristics, e.g. spatial flood extent and temporal flood progression. While previous studies have either linked flood occurrence to weather patterns neglecting the hydrological pre-conditions or categorised floods according to their generating mechanisms into flood types, this study combines both approaches. Exemplary for the Elbe River basin, the influence of pre-event soil moisture as an indicator of hydrological pre-conditions, on the link between weather patterns and flood occurrence is investigated. Flood favouring soil moisture and weather patterns as well as their combined influence on flood occurrence are examined. Flood types are identified and linked to soil moisture and weather patterns. The results show that the flood favouring hydro-meteorological patterns vary between seasons and can be linked to flood types. The highest flood potential for long-rain floods is associated with a weather pattern that is often identified in the presence of so called ‘Vb’ cyclones. Rain-on-snow and snowmelt floods are associated with westerly and north-westerly wind directions. In the analysis period, 18% of weather patterns only caused flooding in case of preceding soil saturation. The presented concept is part of a paradigm shift from pure flood frequency analysis to a frequency analysis that bases itself on process understanding by describing flood occurrence and characteristics in dependence of hydro-meteorological patterns.
Highlights
Floods are generated by the interaction of various physical processes
For 18% of weather patterns, past flood occurrence is restricted to the coincidence with these two soil moisture patterns, i.e. they have only led to flood occurrence in case of preceding soil saturation
Our presented approach is a step in the direction of the concept of ‘flood frequency hydrology’ introduced by Merz and Blöschl (2008a,b)
Summary
Floods are generated by the interaction of various physical processes. These include hydrological pre-conditions (e.g. soil saturation, snow cover), meteorological conditions (e.g. amount, intensity and spatial distribution of precipitation), runoff generation processes (e.g. infiltration and lateral runoff on hillslopes), as well as river routing (e.g. superposition of flood waves). Due to the small sample size of flood events compared to the overall number of days, Prudhomme and Genevier (2011) raised the question ‘‘if any link [between flood occurrence and circulation patterns] found is not a consequence of specific samples of events but truly is representative of physical processes’’ To date, this question, if and to which extent large-scale circulation patterns and flood generating processes are related, has not been explicitly addressed. We identify flood types at the regional scale of the Elbe catchment, based on an adaptation of the flood typology of Merz and Blöschl (2003) and analyse their relationship to circulation patterns.
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