Early warning systems for natural hazards and risks

Abstract

Natural hazards pose an increasing threat to society. Processes change in magnitude and frequency and exposures are modified within short time periods over large areas. Despite our increasing knowledge, the damage tolls due to natural hazards seem to be on the rise. Therefore, a comprehensive risk management strategy is needed to reduce the disaster risks. Within a sustainable management of disaster risks, the installation of an early warning system is often a cost-effective risk mitigation measure, and in some instances the only suitable option.Consequently, the guest editors decided to convene a session within the European Geoscience Union conference to present different early warning systems for natural hazards, independent of whether these deal with landslides, floods, tsunamis, earthquakes, droughts or hydro-meteorological events. The invited presentations addressed conceptual issues, already operating installations or planned systems. It was highlighted that the session was not explicitly focussing on single hazards, but rather addressing the different approaches taken to install, monitor and analyse the hazards. In addition, any research on the establishment of warning thresholds, the communication chain and the prevention strategies were welcome. In total, six oral presentations and 11 poster presentations were received and presented during the conference. These were structured into the different sections: Integrative Warning Systems, Earthquake Warning Systems, Landslide and Debris Flow Warning Systems and Challenges in Early Warning. Out of the 17 presentations, seven papers that provide an overview of related specific topics have been accepted for this topical volume.

Technical Note: An operational landslide early warning system at regional scale based on space–time-variable rainfall thresholds

“…Landslide early warning systems (EWSs) are important tools for the scientific community, even if their potential is not yet fully exploited by society at large, including governments and decision makers (Baum and Godt, 2010;Intrieri et al, 2013;Glade and Nadim, 2014). In landslide-related hazards, many examples of site-specific EWSs have been reported (Michoud et al, 2013, and references therein), but when the area to be monitored is large (e.g., tens of thousands of squared kilometers -hereafter referred to as regional scale), EWSs are not so well established and the description of new case studies is needed.…”

Assessing the performance of regional landslide early warning models: the EDuMaP method

“…The state of knowledge and resources available to issue alerts of precipitation-induced shallow, rapidly moving landslides and debris flows vary across the USA; for instance, in the city of Seattle, WA, the alert system includes four levels -Null, Outlook, Watch and Alarm -and warnings are based on the measured or expected exceedance of cumulated rainfall and intensity-duration thresholds combined with criteria using monitored soil moisture (Godt et al, 2006). In Hong Kong (Chan and Pun, 2004;Cheung et al, 2006; http://www.weather.gov.hk/wservice/ warning/landslip.htm), the correlation model between rainfall events and landslides is based on an increasing probability of landslide occurrence depending on the measured rolling 24 h rainfall for four different types of man-made slopes: soil cuts, rock cuts, fills and retaining structures.…”

“…Landslide early warning systems (LEWSs) mitigate the risk to life associated with the occurrence of landslides by temporarily removing people -i.e., the elements at risk -from hazardous areas whenever landslide risk is considered to be unacceptable. According to Glade and Nadim (2014), the installation of an early warning system is often a cost-effective risk mitigation measure and in some instances the only suitable option for sustainable management of disaster risks. Within the landslide risk management framework proposed by Fell et al (2005), landslide early warning systems may be considered a non-structural passive mitigation option to be employed in areas where risk, occasionally, rises above previously defined acceptability levels.…”

“…Especially for LEWSs operating at regional scale (ReLEWSs), empirical evaluations are often carried out by simply analyzing the time frames during which significant high-consequence landslides occurred in the test area (Keefer et al, 1987;Baum and Godt, 2010;Capparelli and Tiranti, 2010;Aleotti, 2004). Alternatively, the performance evaluation is based on 2 by 2 contingency tables computed for the joint frequency distribution of landslides and alerts, both considered as dichotomous variables (Yu et al, 2003;Cheung et al, 2006;Godt et al, 2006;Restrepo et al, 2008;Tiranti and Rabuffetti, 2010;Kirschbaum et al, 2012;Martelloni et al, 2012;Peres and Cancelliere, 2012;Staley et al, 2013;Lagomarsino et al, 2013Lagomarsino et al, , 2015Greco et al, 2013;Segoni et al, 2014;Gariano et al, 2015;Stähli et al, 2015). The four elements of these tables -i.e., correct alerts (CAs) or true positives; missed alerts, false negatives or type II errors; false alerts, false positives or type I errors; true negatives (TNs) -are then used to assess the weight of the correct predictions in relation to the model errors by means of a series of statistical indicators of the model performance.…”

Adapting the EDuMaP method to test the performance of the Norwegian early warning system for weather-induced landslides

“…According to Glade and Nadim (2014), the installation of an EWS is often a costeffective risk mitigation measure and in some instances the only suitable option for sustainable management of disaster risks. Rainfall-induced warning systems for landslides are, by far, the most diffuse class of LEWSs operating around the world.…”