Abstract:

ak data, catchment area and occurrence date for 99 events (69 from the North-Western region and 30 from the South-Eastern region). Analysis is carried out in terms of relationship of flood peaks with catchment area and sea- sonality. Results show that the envelope curve for the South- Eastern region exhibits a more pronounced decreasing with catchment size with respect to the curve of the North-Western region. The differences between the two relationships reflect changes in the effects of storm coverage and hydrological characteristics between the two regions. Seasonality analy- sis shows that the events in the North-Western region tend to occur between August and November, whereas those in the South-Eastern area tend to occur in the period between October and May, reflecting the relevant patterns in the syn- optic conditions leading to the intense precipitation events. In the second part, the focus is on the rainfall-runoff rela- tionships for 13 selected major flash flood events (8 from the North-Western area and 5 from the South-Eastern area) for which rainfall and runoff properties are available. These flash floods are characterised in terms of climatic features of the impacted catchments, duration and amount of the gener- ating rainfall, and runoff ratio. Results show that the rainfall duration is shorter and the rainfall depth lower in the South- Eastern region. The runoff ratios are rather low in both re- gions, whereas they are more variable in the South-Eastern area. No clear relationship between runoff ratio and rainfall depth is observed in the sample of floods, showing the major influence of rainfall intensity and the initial wetness condi- tion in the runoff generation for these events.

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