Experiences from site-specific landslide early warning systems

Landslide early warning systems (EWSs) have to be implemented in areas with large risk for populations or in- frastructures when classical structural remediation measures cannot be set up. This paper aims to gather experiences of existing landslide EWSs, with a special focus on practical requirements (e.g., alarm threshold values have to take into account the smallest detectable signal levels of deployed sen- sors before being established) and specific issues when deal- ing with system implementations. Within the framework of the SafeLand European project, a questionnaire was sent to about one-hundred institutions in charge of landslide man- agement. Finally, we interpreted answers from experts be- longing to 14 operational units related to 23 monitored land- slides. Although no standard requirements exist for design- ing and operating EWSs, this review highlights some key elements, such as the importance of pre-investigation work, the redundancy and robustness of monitoring systems, the establishment of different scenarios adapted to gradual in- creasing of alert levels, and the necessity of confidence and trust between local populations and scientists. Moreover, it also confirms the need to improve our capabilities for failure forecasting, monitoring techniques and integration of water processes into landslide conceptual models.