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Reliability of Warning and Alarms


In collaboration with the Swiss Federal Office for Civil Protection (FOCP), the SLF has created a method of evaluating early warning systems (EWS) for natural hazards. It assesses the ability of early warning systems to mitigate a certain risk. A practical guide has been produced on the basis of the scientific findings.

In recent years, agencies responsible for dealing with natural hazards have been making increased use of EWS to devise protections against such events. The purpose of such systems is to prevent personal injury in endangered settlements, on roads and railway routes. A cost-effectiveness analysis can evaluate the extent to which such early warning systems are actually capable of reducing risks resulting from natural hazards. In this context, effectiveness is measured by the reduction in risk brought about by a given implemented measure.

The aim of the project entitled "ReWarn – Reliability of Warning and Alarms" was to develop a method enabling interested parties to assess for the first time the effectiveness of early warning systems. Thereby EWS can be compared with and evaluated alongside other protective measures, such as rockfall nets and avalanche barriers, in order to identify cost-effective strategies for minimising risk.

Three objectives were defined and pursued (Fig. 1):

Objective 1:

To define a method of classifying early warning systems as either an alarm, warning or forecasting system. The outcome would serve as a basis for performing a structured evaluation of existing EWS.

Objective 2:

To conduct two case studies (Fig. 2) with the aim of examining the effectiveness of two existing EWS and developing suitable methods. The Illgraben (Valais) case study assessed an alarm system for natural debris flows, and the Preonzo (Ticino) case study evaluated a warning system for slowly developing rockfalls.

Objective 3:

To develop a generally applicable approach for assessing the reliability of local early warning systems, thereby establishing their effectiveness.

To produce a practical guide to summarise the key outcomes of objectives 1 and 2; and help decision-makers plan and operate cost-effective early warning systems.


Practical guide to the deployment of early warning systems

The results of the ReWarn project have been documented in a dissertation and in the practical guide. The purpose of the guide is to present practitioners with a readily comprehensible outline of the scientific findings that are recorded in the dissertation. It helps decision-makers to plan, implement and operate reliable and cost-effective early warning systems, and contains decision-making aids and checklists. The target group includes natural hazards experts from the Swiss cantons (often representing decision-makers of the local authorities and cantons), engineering offices as well as competent employees at private enterprises.

The practical guide comprises three sections:

1 Basic principles/knowledge

2 Decision-making aids/checklists

3 Examples of early warning systems