Especially in alpine terrain areas land slides are one of the most minatory risks to human life, possessions and infrastructure. Even if the trigger for a catastrophe often is a singular circumstance, like e.g. heavy rainfall, most of the threatening slopes are known moving long before and therefore can be monitored. A better understanding of the physical und geological factors as well as the dynamics of the movement and its influencing factors lead to advanced options in rating the risks and, if necessary, take counteractions in time.

Early warning systems (EWS) are increasingly applied for mitigating natural hazard risks, but their effect on risk reduction and their economic benefit has rarely been evaluated in a quantitative way. The project ReWarn was initiated to develop a method for assessing the effectiveness and the reliability of EWS. A guideline summarizes the most important findings of the project to support decision makers, who are in charge of planning and operating EWS. In a first step, we provide a classification for site - specific EWS, which are divided into alarm and warning systems. In a second step, we quantitatively determine the factors that influence the reliability for each system class with respect to i) technical reliability and ii) inherent reliability. A technically reliable EWS is based on a redundant system configuration and a control system; its components are protected from external failure sources. The inherent reliability of the EWS is increased through a multi - level monitoring approach and depends on warning thresholds, the selection of appropriate sensors and sensor locations, the quality of models and human response. These and other findings are collected in the guidelines in a comprehensive form, to support practitioners in developing and operating reliable and cost-efficient EWS.

This project is carried out in collaboration with SLF Davos (Martina Sättele & Dr. Michael Bründl) Related publications: Sättele M., Bründl M., Straub D.: Reliability and Effectiveness of Warning Systems for Natural Hazards: Concepts and Application to Debris Flow Warning