Hydrological extremes: controls, spatial & temporal variability and regional patterns (Session HS36, EGU General Assembly 2007)

Floods and droughts are the major weather related hydrological disasters and recent events have demonstrated Europe’s continuing exposure to these natural hazards. High and low flows and associated floods and droughts are natural phenomena caused by meteorological anomalies and modified by the physical characteristics of catchments. The knowledge about the quantity, timing and risk of extreme discharges during floods and droughts is the basic requirement for a broad range of purposes in hydrology and water resources management. This knowledge has ideally to be based on the understanding the controls of the genesis of hydrological extremes (like the importance of landscape heterogeneities, threshold processes, scaling issues), finding appropriate ways how to characterize them (spatial and temporal variability, regional patterns) and designing reliable methods of predicting. Hydrological models based on physical concepts, statistical or regional approaches are used to define relationships between extreme flows, their characteristics and basin properties in order to predict characteristics of extremes at gauged and ungauged sites. The knowledge of the dominant processes of a study area is essential to pursue this task, and there is consensus among modellers that the parsimony of models is one important factor of predictive performance. The main objectives of this session are (a) to foster the understanding of the main governing processes of floods and droughts, (b) to discuss modeling approaches and concepts how to include process understanding in predictive models, (c) to shed light on the regional characteristics and spatial patterns of floods and droughts and the processes that give rise to such patterns including climate forcing, extreme precipitation and catchment response, (d) to present methods for estimating and/or predicting floods, droughts and low flows at a regional scale as well as regional methods for making predictions at the local scale, (e) to learn from practical applications of such models, (f) to profit from the similarity and differences of modeling concepts for both extremes. Specifically, papers are solicited that address one or more of the following questions: - what are the important mechanisms producing regional extremes, and how the use of diverse hydrological methods can contribute to highlighting the governing processes - what is the role of climatic forcing and catchment properties in the regional distribution of extremes, - which hydro-meteorological and catchment characteristics and indices can be used to describe regional patterns of extremes, - how do anthropogenic impacts and different land use patterns affect the spatial patterns of regional extremes, - how effective and reliable are the multivariate statistical techniques (e.g., cluster analysis, artificial neural networks, copulas, etc.) for identification of watersheds with similar dominant hydrological characteristics The scope of the session includes both general methodological contributions and case studies in different regions.