Why do some catchments exhibit a more flashy response? Catchment parameters controlling flash flood generation.

To assess flash flood susceptibility, an analysis of physiographic parameters of catchments affected by flash floods in the past was conducted. The study focuses on 17 catchments, ranging from 9 to 80 km², with water gauge stations in the Czech Republic. Based on parameters such as catchment area, slope, elevation, Melton ratio, river length and slope, river network length and density, shape index, arable land proportion, curve number, and road network density, categorization into clusters I–III was performed using principal component analysis and k-medoids clustering. To evaluate the hydrological response in relation to these parameters, the flashiness index (quantifying the magnitude and timing of the flood wave) was calculated for events in which peak discharge exceeded the 1-year return period discharge. The results show that the highest flashiness values were recorded in a group of small, steep catchments characterized by high terrain roughness, maximum elevations, a dense river network, and compact shape.