Tuesday, October 18, 2011

Marco Borga's talk

Marco concentrated mainly on the interplay between rainfall and the catchment structure, as derived from the data of his Hydrate EU project. Interestingly he introduced (after, he said, initial suggestions from Jim Smith) some spatial moments (i.e. the moments of the spatial distribution of the rainfall with respect to the catchment) to quantify the storm movements during flood events. His results shows that usually storm can be considered almost stationary (on average) over the catchments, but some events are more strongly characterized than other, and especially, concentrating close to the mountain ridge. This cannot be obviously a general result, since around the World the relative position of the relative location of storm to the catchment can be different. What is of general importance is that the space-time evolution of storms can be of some relevance in producing flash floods, and that now we have a statistical tool for quantifying these storms.

 Here it is Marco's abstract on his seminar: Spatial moments of catchment rainfall: rainfall spatial organisation, basin morphology and flood response

 "In this talk I will introduce a general analytical framework for assessing the dependence existing between spatial rainfall organisation, basin morphology and runoff response. The analytical framework builds upon a set of spatial rainfall statistics (termed ‘spatial moments of catchment rainfall’) which describe the spatial rainfall organisation in terms of concentration and dispersion statistics as a function of the distance measured along the flow routing coordinate. The introduction of these statistics permits derivation of a simple relationship for the quantification of storm velocity at the catchment scale. The talk illustrates the development of the analytical framework and explains the conceptual meaning of the statistics by means of application to five extreme flash floods occurred in various European regions in the period 2002-2007. High resolution radar rainfall fields and a distributed hydrologic model are employed to examine how effective are these statistics in describing the degree of spatial rainfall organisation which is important for runoff modelling. This is obtained by quantifying the effects of neglecting the spatial rainfall variability on flood modelling, with a focus on runoff timing. The size of the study catchments ranges between 36 to 982 km2. The analysis reported here shows that the spatial moments of catchment rainfall can be effectively employed to isolate and describe the features of rainfall spatial organization which have significant impact on runoff simulation. These statistics provide essential information on what space–time scales rainfall has to be monitored, given certain catchment and flood characteristics, and what are the effects of space–time aggregation on flood response modeling."

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