SCALES OF RAINFALL TRIGGERS AND LANDSLIDING

R. Dikau and L. Schrott (Geographische Institute, Universitaet Bonn, Meckenheimer Allee 166, D-53115 Bonn, Germany)

The paper deals with conceptions, theories and results of different approaches to relate rainfall triggers with landslide processes. In a first section general approaches with respect to the terminology of triggers and ground dispositions are discussed including a classification of different thresholds types in space and time. A prerequisite for discussing hydrogeological triggers is a detailed consideration of climate and rainfall. Therefore, a second section is concerned with basic statements about recent and past rainfall/climate variabilities in relation to periodic and episodic landslide events. Diffused landsliding, by which we understand, landslide events affecting large regions, can be caused by other rainfall conditions than local phenomena. They occur in different recurrence intervals and spatial extensions. This implies considerations of the frequency of atmospheric circulation patterns, which are derived from large scale atmospheric circulations. A discussion of diffused rainfall thresholds has to include these aspects. If landsliding and rainfall triggers are correlated, different space and time scales have to be considered. However, only in very limited areas in Europe adequate data of diffused landsliding are available. Despite of the socio-economic importance of landsliding in a variety of European regions, no appropriate methodology has been developed to synthesize knowledge and research activities. Therefore, proposals are presented for an European database, which could serve as a data source and tool for future landslide research.