the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 25 Jul 2024
What can we learn from global disaster records about multi-hazards and their risk dynamics?
Abstract. Recent studies have been reporting more extreme, compounding impacts from multi-hazards than from single hazard events owing to complex interrelationships of hazard, exposure and vulnerability in a multi-hazard setting. However, our current understanding of multi-hazard impacts is primarily based on case studies of individual events. To complement this, we examine the disaster records of the global emergency events database EM-DAT for the period 2000–2018 for evidence of multi-hazard risk dynamics. We develop an algorithm to identify multi-hazard events which uses the information on associated hazards as well as spatiotemporal relationships between disaster records in EM-DAT. We then perform a statistical analysis to assess potential risk dynamics in reported impacts of selected hazard pair types. We identified that twice as many hazards are part of multi-hazard events when considering a spatial overlap of at least 25 % and a time lag of at most 1 year between disaster records in addition to the information of associated hazards. These multi-hazard events account for 78 % of the total damages, 83 % of the total people affected and 69 % of the total deaths in the reported disasters. The statistical comparison indicates that there are different patterns of how impacts compound depending on the impact metric as well as the hazard type. However, as a general trend, hazard pairs seem to have at least as or more impact than two isolated single hazards. To capture the patterns and to integrate them into risk analysis and decision making, we propose the development of generic archetypes of multi-hazard risk dynamics. Despite the well-known limitations of EM-DAT related to completeness of the records as well as reliability of the impact data, which prevents detailed analyses of the data, we found the database useful for exploring high-level patterns at the global scale. Nonetheless, the uncertainties and limitations encountered highlight that future research should be directed at improving and supporting the multi-hazard and impact information in EM-DAT.
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RC1: 'Comment on nhess-2024-134', Anonymous Referee #1, 08 Sep 2024
This study presents “an algorithm to identify multi-hazard events which uses the information on associated hazards as well as spatiotemporal relationships between disaster records in EM-DAT.” The topic is both relevant and timely, and the manuscript is generally well-written. However, I recommend that the authors address the following points before the manuscript is considered for publication:
- The authors assert that there is a lack of understanding regarding historical multi-hazard impacts, yet the introduction does not adequately explain why assessing multi-hazard impacts is particularly challenging. I recommend the authors provide a more detailed explanation of the complexities involved in evaluating multi-hazard impacts.
- The introduction would benefit from restructuring. After outlining the study's aim, the authors introduce uncertainties associated with the use of EM-DAT, as well as how this global dataset is utilized in the current study. I suggest removing the text from lines 75–99 and incorporating it into sections 2.1 EM-DAT and 5 Discussion for better clarity and flow.
- The criteria for multi-hazard classification in this study are unclear. In section 3.1.2, the authors mention restricting multi-hazard events with an intersecting area smaller than 50%. However, previous studies have outlined various types of multi-hazard events, including preconditioned, triggering, multivariate, spatially compounding, and temporally compounding events. Multi-hazards can also occur in multiple interconnected locations within a limited timeframe. Given this, I am unsure how the authors justify the following statement: “We reason that the smaller the intersecting area of two footprints, the less likely that the actual disaster impact zones overlap. The idea behind the threshold is to keep only those combinations that have a reasonable likelihood of actually having overlapping disaster zones.”
- Figure 1 requires further elaboration. Including only subsection headings does not sufficiently clarify the overall methodological approach used in the study. I suggest the authors develop a more comprehensive methodological flow diagram to better explain the proposed approach.
Citation: https://doi.org/10.5194/nhess-2024-134-RC1 -
RC2: 'Comment on nhess-2024-134', Anonymous Referee #2, 14 Oct 2024
This study makes a valuable and timely contribution to disaster risk science by developing an algorithm that identifies multi-hazard events, utilising information on associated hazards as well as spatiotemporal relationships between disaster records in EM-DAT. The statistical analysis reveals that hazard pairs often lead to greater or at least equal impacts compared to isolated single hazards, although the patterns of impact vary depending on the hazard type and the impact metric. The study proposes developing generic archetypes of multi-hazard risk dynamics to enhance risk analysis and decision-making. While acknowledging the limitations of the EM-DAT database, it demonstrates the database’s utility for identifying global patterns of multi-hazard impacts and recommends improvements in data reporting.
The manuscript is generally well-written and addresses an important topic, but several revisions could enhance its clarity, structure, and impact. I recommend the following adjustments to strengthen the manuscript before publication:
Methodology and Detail:
The methodology is sound, but providing more detail about the "statistical methods" previously used (Lines 94–95) would offer readers a clearer understanding of previous research. Additionally, the manuscript would benefit from justifying the focus on spatial overlap within a single country (Section 3.1.2). For instance, the author could explain why potential transboundary, spatially compounding events, such as those across northern Europe, were not considered (e.g., Fang et al., 2024; De Luca et al., 2017; Berghuijs et al., 2019). The inclusion of Figure 1 is valuable, but expanding its caption to provide more context would help readers understand it without needing to refer back to the main text.
Structure:
The manuscript would benefit from a more cohesive structure. For example, moving background information currently placed in the results section (e.g., Line 279) into the methods section would help maintain continuity and allow the results section to focus more directly on presenting findings. Additionally, keeping the discussion and results sections distinct would improve the paper’s flow. Any interpretive content (e.g., Line 301) could be relocated to the discussion. Furthermore, separating recommendations from the conclusion would also allow the paper to finish on a stronger note, with a distinct conclusion leaving a lasting impression. Finally, introducing the archetypes (Line 427 onwards) in more detail in the methods section could help readers appreciate their relevance from the start, enhancing the manuscript's overall coherence.
Writing Style:
The clarity of the manuscript can be improved by adopting a more concise and direct tone across all sections. For example, removing phrases like "not surprisingly" (e.g., Line 338) and simplifying explanations (e.g., Line 384 regarding spatiotemporal overlaps) would make the writing more focused. Writing all sections more concisely will help maintain a tighter narrative; for example, understanding Lines 480–484 currently requires multiple readings.
Here are three specific examples that would benefit from revision for clarity and conciseness, although consider making changes throughout the manuscript:
- Line 137 – Correct the typographical error "other the other."
- Line 141 – Consider rewriting this sentence to improve its flow.
- Line 488 – Ensure consistent tense usage throughout the text.
Citation: https://doi.org/10.5194/nhess-2024-134-RC2
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