August 8, 2024

By Silvia De Angeli , posted on the blog of the Natural Hazards (NH) Division of the European Geosciences Union (EGU)Read the original article here Photo credit, from top left to bottom right: Pamela Trisolino (via Imaggeo), Michiel Baatsen (via Imaggeo), Stefan Doerr (via Imaggeo), Dimitri Defrance (via Imaggeo), Katja Bigge (via Imaggeo), Babak Hejrani (via Imaggeo), Elias Sch (via Pixabay) and Dan Killam (via Imaggeo). With the Natural Hazards 101 series, we mean to bring our readers closer to the terminology often used in the field of natural hazards, but that may not be so familiar. In the first episode of the series, we focused on the definition of hazard and natural hazard. We moved then to the concepts of risk, disaster risk management, and the forecasting and modelling of natural hazards. In this episode, we will explore the meaning of multi-hazards and multi-hazard risk. According to UNDRR [1], the multi-hazard concept refers to “(1) the selection of multiple major hazards that the country faces, and (2) the specific contexts where hazardous events may occur simultaneously, cascadingly or cumulatively over time, and taking into account the potential interrelated effects.” These definitions of multi-hazard represent two major categories in which multi-hazard approaches can be classified: (i) independent multi-hazards approaches, where single hazards are just overlayed and treated as independent phenomena, and (ii) approaches that consider multiple hazards and their potential interactions. Single hazard and independent multi-hazards approaches could potentially underestimate the risk leading to inadequate disaster risk reduction measures. Although more challenging and demanding, the approaches that consider multiple hazards and their potential interactions are better able to capture the real risk in many areas of the world. The interactions between hazards are diverse and complicated, which leads to differences in the literature regarding the identification and classification of these interactions (see for example, [2, 3,4]). However, it is possible to identify some basic mechanisms of interaction: Triggering is when one hazard directly triggers another, generating what is called a “domino effect” or “triggering mechanism” among hazards. This is the case of the Great East Japan Earthquake that struck in the Pacific Ocean off the northeast coast of Japan’s Honshu island in 2011 and triggered a massive tsunami that flooded more than 200 square miles of coastal land [5]. Influence is when one hazard can influence another hazard, for example, changing its probability of occurrence or magnitude, without acting as a trigger. A typical example is the removal of protective forest by an avalanche in winter that leads to higher frequency and magnitude of rock falls during summer [6]. Coincidence is when hazards occur in the same place simultaneously independently from the causal dependence among them. For example, the volcanic eruption of Mount Pinatubo in the Philippines in 1991 coincided with the intense rainfalls caused by the passage of Typhoon Yunya [2]. In contrast to single hazard events, the assessment of multiple hazards and their relationships poses a series of challenges in each step of the risk analysis: from the assessment of the hazard level to the vulnerability analysis and the resultant risk level. Indeed, hazard dependencies may influence the overall hazard level and the vulnerability of elements at risk. As an emerging focus of research and interest, the multi-hazard risk still lacks a common and standard definition and glossary among the different communities [7]. Some authors distinguish between ‘multi-hazard risk’ and ‘multi-risk’. Kappes et al. [6] define multi-hazard risk as a risk evaluation that considers the impact of multiple hazards, and multi-risk as related to the assessment of multiple risks such as economic, ecological, social, etc. Other authors [8, 9] use the term multi-risk to define an approach that determines the whole risk from several hazards, accounting for possible hazards and vulnerability interactions entailing both a multi-hazard and multi-vulnerability perspective. The concept of multi-vulnerability refers to “the ensemble of interconnected and dynamic vulnerabilities among different exposed elements” [9]. For physical vulnerability assessments, multi-vulnerability mainly refers to the development of multi-hazard damage or fragility functions (for example, [10]), able to model the damage caused by simultaneous or subsequent hazards on the same exposed element. Multi-hazard risk (or multi-risk) approaches are crucial to define successful disaster risk reduction measures. Traditionally, disaster risk reduction measures are implemented to decrease the risk of a single hazard type despite their potential of having unwanted effects on other hazard typologies. These potentially negative effects between measures are defined by de Ruiter et al. [11] as ‘asynergies’. For example, building on stilts is an often-used measure to decrease a building’s flood vulnerability; however, it simultaneously increases its earthquake vulnerability [11]. Multi-hazard risk approaches allow improving the understanding of these asynergies, identifying measures able to successfully reduce the impacts of disasters across different hazards. Please consider that this post does not aim to provide an exhaustive literature review on multi-hazard risk but only provides examples to support the presented concepts and definitions. Read episode 1: What is a -natural- hazard? Read episode 2: The concept of risk. Read episode 3: The disaster cycle. Read episode 4: Forecasting and modelling. References [1] https://www.undrr.org/terminology#R [2] Gill, J. C., & Malamud, B. D. (2014). Reviewing and visualizing the interactions of natural hazards. Reviews of Geophysics, 52(4), 680-722. https://doi.org/10.1002/2013RG000445 [3] Liu, B., Siu, Y. L., & Mitchell, G. (2016). Hazard interaction analysis for multi-hazard risk assessment: a systematic classification based on hazard-forming environment. Natural Hazards and Earth System Sciences, 16(2), 629-642. https://doi.org/10.5194/nhess-16-629-2016 [4] Tilloy, A., Malamud, B. D., Winter, H., & Joly-Laugel, A. (2019). A review of quantification methodologies for multi-hazard interrelationships. Earth-Science Reviews, 196, 102881. https://doi.org/10.1016/j.earscirev.2019.102881 [5] Mimura, N., Yasuhara, K., Kawagoe, S., Yokoki, H., & Kazama, S. (2011). Damage from the Great East Japan Earthquake and Tsunami-a quick report. Mitigation and adaptation strategies for global change, 16(7), 803-818. https://doi.org/10.1007/s11027-011-9297-7 [6] Kappes, M. S., Keiler, M., von Elverfeldt, K., & Glade, T. (2012). Challenges of analyzing multi-hazard risk: a review. Natural hazards, 64(2), 1925-1958. https://doi.org/10.1007/s11069-012-0294-2 [7] Gallina, V., Torresan, S., Critto, A., Sperotto, A., Glade, T., & Marcomini, A.

By Hedieh Soltanpour, posted on the blog of the Natural Hazards (NH) Division of the European Geosciences Union (EGU)Read the original article here Visualising Earth’s Dynamic Hazards. This illustration displays a range of natural hazards, from geological to meteorological, presented in a continuous landscape to emphasise the interconnected nature of these dynamic events. (Image created with OpenAI, DALL.E (2024)) Understanding multi-hazard approaches is crucial in an era of escalating natural hazards leading to disastrous impacts on Earth’s citizens. Triggered by the increasing frequency and severity of these events, this brief post provides a concise yet comprehensive overview of evolving paradigms in multi-hazard research and management. By exploring definitions, historical developments, and current trends, we highlight the critical importance of integrated strategies in mitigating impacts on society all in a nutshell. Foundation: Multi-hazard concept history at one glance It is important to acknowledge that the encouragement of multi-hazard approaches began with the work of Hewitt and Burton (1971) [1]; they emphasised the necessity of systematic cross-hazard approaches in understanding the hazard landscape of an area. However, the importance of multi-hazards was pronounced when this concept was first introduced in the United Nations’ Agenda 21 for Sustainable Development, held in Rio de Janeiro, Brazil, in 1992 under the title of “complete multi-hazard research” [2]. Subsequent international frameworks, including the Johannesburg Plan (UN, 2002), the Hyogo Framework for Action (2005) [3], and the more recent Sendai Framework for Disaster Risk Reduction (2015-2030) [4], have further underscored the importance of these strategies. The Sendai Framework, for instance, highlights the necessity for multi-hazard approaches, defining them as “the selection of multiple major hazards faced by a country, including the specific contexts in which hazardous events may occur simultaneously, cascadingly, or cumulatively over time, with consideration for their potential interrelated effects” [2]. Since then, the field has seen an exponential increase in research across various dimensions of multi-hazards, ranging from social to physical aspects [for example, 5-6]. This trend has persisted, reaching a point where the term “multi-hazard” has become a common buzzword in nearly every project related to natural hazards [7]. The unfolding story: Initial and ongoing confusion Initially, due to the unclear and varied definition of multi-hazards, studies mainly adopted approaches based on their own perceptions of this term, ranging from an “all-hazards-at-a-place approach” [1] to “more-than-one-hazard” approaches [8]. Kappes (2012) [8] provided an early definition of “multi-hazard” within the framework of risk reduction as “the totality of relevant hazards in a defined area”. This concept aimed to cover all potential environmental or man-made threats that could lead to harm, damage, or degradation. However, the criteria for defining the relevance of a hazard have been subject to debate, ranging from the introduction of a damage-based cut-off point for relevance by Hewitt and Burton (1971) [1], to the European Commission (2011) [9] proposing criteria based on the scale and impact of a hazard [8]. The traditional approach treats each hazard individually as a single event, often confusing decision-makers, particularly in critical circumstances. Managing natural hazards in isolation fails to recognise the interconnection and potential cascading effects that can arise from multiple hazards [8, 10-11]. Gill and Malamud (2016) [11] argue that narrowing the focus to a limited portion of the entire Earth system instead of understanding its dynamic interactions as a whole could lead to decisions that increase vulnerability to overlooked hazards. Consequently, the prevalence of single-hazard approaches inevitably leads to a distortion of management priorities. (Image created by OpenAI, DALL.E (2024)) Modelling perspective: Challenges in multi-hazard mapping Subsequently, multi-hazard mapping could not evidently remain safe from this ambiguity. Multi-hazard/ susceptibility maps are used to communicate complex scientific data with stakeholders. These maps serve as a communication tool to support and aid decision-makers by providing valuable information regarding disaster preparedness mitigation measures and informing urban planning and public policy [12]. To avoid single-hazard approaches, many analyses turned to superimposing separately modelled single hazards in a given area, which they are better called a multi-layer single-hazard approach [11], which is similar to the all-hazards-at-a-place approach, causing the same challenges in practice. In this regard, a full multi-hazard assessment/mapping has been encouraged, where the interrelationships of hazards (triggering, amplifying, compound and consecutive events) are also considered. The final thought: A question mark Moving beyond only assessing individual hazards is essential to manage natural hazards better. Equally important is gaining insights into the complex interplay between various hazards and their cascading relationships and effects. Since natural hazards do not occur in isolation but often exacerbate each other, leading to compounded effects, the strategies for understanding and mitigating them must also be collaborative, drawing from a wide range of scientific disciplines. When different hazards join forces to unleash significant damage, why should not scientists from various fields do the same? Just as these hazards compound their impact by working in tandem, our response should be equally collaborative, bringing together diverse expertise to tackle the challenge head-on. The fundamental step towards this collaboration is facilitating effective communication by establishing a common language where all different terms, yet conveying more or less the same concept, can be understood when discussing multi-hazards and their impacts on society. References [1] Hewitt K, Burton I (1971) Hazardousness of a place: a regional ecology of damaging events. Toronto Press, Toronto [2] UNEP (1992) Agenda 21. Tech. rep., United Nations Environment Programme [3] UNISDR, 2005. Hyogo Framework for Action 2005-2015: Building the Resilience of Nations and Communities to Disasters. United Nations, Hyogo, Japan [4] UNISDR. Sendai Framework for Disaster Risk Reduction 2015–2030. In UN Report UNISDR/GE/015; United Nations Office for Disaster Risk Reduction: Geneva, Switzerland [5] Joffe, H., Potts, H. W., Rossetto, T., Doğulu, C., Gul, E., & Perez-Fuentes, G. (2019). The Fix-it face-to-face intervention increases multihazard household preparedness cross-culturally. Nature human behaviour, 3(5), 453-461 [6] Tilloy, A., Malamud, B.D., Winter, H., Joly-Laugel, A., 2019. A review of quantification methodologies for multi-hazard interrelationships, 102881–102881 Earth-sci. Rev. 196 [7] Al-Khalili, J. host. (2023, June 6). Bruce Malamud on modelling risk for natural hazards. The life scientific