The use of rainfall radar for the prediction of shallow landslides and debris flows

Patrick Gamma1, Markus Zimmermann2, Serena Liener3
Geo7 Geoscience, Neufeldstr. 3, 3012 Bern, Switzerland,
Tel.: +41-31 300 4433, Fax: +41-31 302 7811,
E-mail: 1gamma@geo7.ch, 2mzimmermann@geo7.ch
3Institute of Geography, Univ. of Bern, Hallerstr. 12, 3012 Bern, Switzerland.
Tel.: +41-31 631 8390, Fax: +41-31 631 8511,
E-mail: liener@giub.unibe.ch

For the analysis of landslides and debris flows, rainfall radar data have increasingly been used in Switzerland during the past few years. The radar provided the necessary prediction data with high spatial and temporal resolution for the back-analysis and post-disaster assessment of the incidents. The experiences made thereby as well as recent developments in disposition models lead to a general design of a warning system for shallow landslides and debris flows for particular catchments. The foundation of such a system is an in-depth understanding of the governing geomorphic processes and the history of past events in the area under consideration. The system is built around the concept of disposition: the basic and the variable disposition describe the readiness of an area for geomorphic processes to occur and thus define the threshold values, whereas a triggering event that exceeds this threshold actually releases it. Spatially distributed models for the disposition together with online radar data for precipitation (accumulated rainfall over long periods, instantaneous triggering rainfall etc.) can deliver an overview of the situation in the catchment. All models used in the system must be verified and calibrated with events and "non-events", and threshold values have to be determined. In future, a warning system for shallow landslides and debris flows, together with other preparedness measures can well contribute to an effective disaster mitigation plan. The quality of the warning system determines the acceptance in the concerned agencies as well as in the population to be warned.