Searching for regularities of slope modelling by extreme events (diversity of rainfall intensity – duration and physical properties of the substrate)

In the last decades, research into slope transformation, especially transformation caused by debris flows and shallow landslides has set great store by the establishment of thresholds based on the relation of mean rainfall intensity to its duration. The present author is no exception. In the 1970s, after examining that relationship he distinguished three main types of extreme rainfalls (heavy downpours, continuous rains and rainy seasons). In this paper, while noting the great diversity of extreme events in space and time, he stresses the function of extremely high rainfall intensity in triggering off the slope transformation. Taking into account the role of such parameters as the effect of substrate, relief and land use on the distribution of precipitation into overland flow, subsurface runoff, and ground water storage, he proposes several models that connect geomorphic processes with different types of extreme rainfalls. In critical comments to the establishment of thresholds based only on mean daily rainfall and mean rainfall intensity he follow the opinion on limitation of factors to standart climatic and hydrologic and hydrologic data presented earlier by T. Dunne and A. Freeze. This analysis also notes the role of clusterings of events in various climatic zones and stresses the need of continuous monitoring of rainfall intensity and any other aspects of water circulation on slopes. All of those elements are indispensable for the construction of a more diversified pattern of thresholds.