Natural Hazards and Earth System Sciences

Abstract. Landslides are a ubiquitous hazard in terrestrial environments with slopes, incurring human fatalities in urban settlements, along transport corridors and at sites of rural industry. Assessment of landslide risk requires high-quality landslide databases. Recently, global landslide databases have shown the extent to which landslides impact on society and identified areas most at risk. Previous global analysis has focused on rainfall-triggered landslides over short ∼ 5-year observation periods. This paper presents spatiotemporal analysis of a global dataset of fatal non-seismic landslides, covering the period from January 2004 to December 2016. The data show that in total 55 997 people were killed in 4862 distinct landslide events. The spatial distribution of landslides is heterogeneous, with Asia representing the dominant geographical area. There are high levels of interannual variation in the occurrence of landslides. Although more active years coincide with recognised patterns of regional rainfall driven by climate anomalies, climate modes (such as El Niño–Southern Oscillation) cannot yet be related to landsliding, requiring a landslide dataset of 30+ years. Our analysis demonstrates that landslide occurrence triggered by human activity is increasing, in particular in relation to construction, illegal mining and hill cutting. This supports notions that human disturbance may be more detrimental to future landslide incidence than climate.

Tóm tắt. Bài báo này xem xét sự phát triển qua thời gian lịch sử của ý nghĩa và cách sử dụng thuật ngữ "khả năng phục hồi". Mục tiêu là làm sâu sắc thêm sự hiểu biết của chúng ta về cách thuật ngữ này được áp dụng trong giảm thiểu rủi ro thiên tai và giải quyết một số mâu thuẫn và tranh cãi đã phát sinh khi nó được sử dụng. Bài báo lần theo sự phát triển của khả năng phục hồi qua các lĩnh vực khoa học, nhân văn và pháp lý, chính trị. Nó xem xét cách mà cơ học đã chuyển giao thuật ngữ này sang sinh thái học và tâm lý học, và từ đó được các nghiên cứu xã hội và khoa học bền vững tiếp nhận. Như một số tác giả đã lưu ý, với tư cách là một khái niệm, khả năng phục hồi liên quan đến một số mâu thuẫn hoặc mâu thuẫn nghiêm trọng, chẳng hạn như giữa sự ổn định và động lực, hoặc giữa trạng thái cân bằng động (nội môi) và sự tiến hóa. Hơn nữa, mặc dù khái niệm khả năng phục hồi hoạt động khá tốt trong khuôn khổ của lý thuyết hệ thống tổng quát, nhưng trong những tình huống mà việc hình thành hệ thống ngăn cản thay vì thúc đẩy sự giải thích, một sự diễn giải khác về thuật ngữ là cần thiết. Điều này có thể xảy ra trong giảm thiểu rủi ro thiên tai, điều này liên quan đến việc chuyển hóa thay vì bảo tồn "trạng thái của hệ thống". Bài viết kết luận rằng sự quan niệm hiện đại về khả năng phục hồi có lợi từ một lịch sử phong phú về các ý nghĩa và ứng dụng, nhưng việc đọc quá nhiều vào thuật ngữ như một mô hình và một khuôn khổ thì có thể nguy hiểm - hoặc ít nhất là có thể mang lại sự thất vọng.

Abstract. Flood disaster mitigation strategies should be based on a comprehensive assessment of the flood risk combined with a thorough investigation of the uncertainties associated with the risk assessment procedure. Within the "German Research Network of Natural Disasters" (DFNK) the working group "Flood Risk Analysis" investigated the flood process chain from precipitation, runoff generation and concentration in the catchment, flood routing in the river network, possible failure of flood protection measures, inundation to economic damage. The working group represented each of these processes by deterministic, spatially distributed models at different scales. While these models provide the necessary understanding of the flood process chain, they are not suitable for risk and uncertainty analyses due to their complex nature and high CPU-time demand. We have therefore developed a stochastic flood risk model consisting of simplified model components associated with the components of the process chain. We parameterised these model components based on the results of the complex deterministic models and used them for the risk and uncertainty analysis in a Monte Carlo framework. The Monte Carlo framework is hierarchically structured in two layers representing two different sources of uncertainty, aleatory uncertainty (due to natural and anthropogenic variability) and epistemic uncertainty (due to incomplete knowledge of the system). The model allows us to calculate probabilities of occurrence for events of different magnitudes along with the expected economic damage in a target area in the first layer of the Monte Carlo framework, i.e. to assess the economic risks, and to derive uncertainty bounds associated with these risks in the second layer. It is also possible to identify the contributions of individual sources of uncertainty to the overall uncertainty. It could be shown that the uncertainty caused by epistemic sources significantly alters the results obtained with aleatory uncertainty alone. The model was applied to reaches of the river Rhine downstream of Cologne.

Abstract. Social vulnerability indices are a means for generating information about people potentially affected by disasters that are e.g. triggered by river-floods. The purpose behind such an index is in this study the development and the validation of a social vulnerability map of population characteristics towards river-floods covering all counties in Germany. This map is based on a composite index of three main indicators for social vulnerability in Germany – fragility, socio-economic conditions and region. These indicators have been identified by a factor analysis of selected demographic variables obtained from federal statistical offices. Therefore, these indicators can be updated annually based on a reliable data source. The vulnerability patterns detected by the factor analysis are verified by using an independent second data set. The interpretation of the second data set shows that vulnerability is revealed by a real extreme flood event and demonstrates that the patterns of the presumed vulnerability match the observations of a real event. It comprises a survey of flood-affected households in three federal states. By using logistic regression, it is demonstrated that the theoretically presumed indications of vulnerability are correct and that the indicators are valid. It is shown that indeed certain social groups like the elderly, the financially weak or the urban residents are higher risk groups.

Abstract. Traditional flood design methods are increasingly supplemented or replaced by risk-oriented methods which are based on comprehensive risk analyses. Besides meteorological, hydrological and hydraulic investigations such analyses require the estimation of flood impacts. Flood impact assessments mainly focus on direct economic losses using damage functions which relate property damage to damage-causing factors. Although the flood damage of a building is influenced by many factors, usually only inundation depth and building use are considered as damage-causing factors. In this paper a data set of approximately 4000 damage records is analysed. Each record represents the direct monetary damage to an inundated building. The data set covers nine flood events in Germany from 1978 to 1994. It is shown that the damage data follow a Lognormal distribution with a large variability, even when stratified according to the building use and to water depth categories. Absolute depth-damage functions which relate the total damage to the water depth are not very helpful in explaining the variability of the damage data, because damage is determined by various parameters besides the water depth. Because of this limitation it has to be expected that flood damage assessments are associated with large uncertainties. It is shown that the uncertainty of damage estimates depends on the number of flooded buildings and on the distribution of building use within the flooded area. The results are exemplified by a damage assessment for a rural area in southwest Germany, for which damage estimates and uncertainty bounds are quantified for a 100-year flood event. The estimates are compared to reported flood damages of a severe flood in 1993. Given the enormous uncertainty of flood damage estimates the refinement of flood damage data collection and modelling are major issues for further empirical and methodological improvements.

Abstract. In light of the recent enhanced activity in the study of tsunami waves and their source mechanisms, we consider tsunami-like waves that are induced by atmospheric processes rather than by seismic sources. These waves are mainly associated with atmospheric gravity waves, pressure jumps, frontal passages, squalls and other types of atmospheric disturbances, which normally generate barotropic ocean waves in the open ocean and amplify them near the coast through specific resonance mechanisms (Proudman, Greenspan, shelf, harbour). The main purpose of the present study is to describe this hazardous phenomenon, to show similarities and differences between seismic and meteorological tsunamis and to provide an overview of meteorological tsunamis in the World Ocean. It is shown that tsunamis and meteotsunamis have the same periods, same spatial scales, similar physical properties and affect the coast in a comparably destructive way. Some specific features of meteotsunamis make them akin to landslide-generated tsunamis. The generation efficiency of both phenomena depend on the Froude number (Fr), with resonance taking place when Fr~1.0. Meteotsunamis are much less energetic than seismic tsunamis and that is why they are always local, while seismic tsunamis can have globally destructive effects. Destructive meteotsunamis are always the result of a combination of several resonant factors; the low probability of such a combination is the main reason why major meteotsunamis are infrequent and observed only at some specific locations in the ocean.

Abstract. Drought is a natural hazard that can cause a wide range of impacts affecting the environment, society, and the economy. Providing an impact assessment and reducing vulnerability to these impacts for regions beyond the local scale, spanning political and sectoral boundaries, requires systematic and detailed data regarding impacts. This study presents an assessment of the diversity of drought impacts across Europe based on the European Drought Impact report Inventory (EDII), a unique research database that has collected close to 5000 impact reports from 33 European countries. The reported drought impacts were classified into major impact categories, each of which had a number of subtypes. The distribution of these categories and types was then analyzed over time, by country, across Europe and for particular drought events. The results show that impacts on agriculture and public water supply dominate the collection of drought impact reports for most countries and for all major drought events since the 1970s, while the number and relative fractions of reported impacts in other sectors can vary regionally and from event to event. The analysis also shows that reported impacts have increased over time as more media and website information has become available and environmental awareness has increased. Even though the distribution of impact categories is relatively consistent across Europe, the details of the reports show some differences. They confirm severe impacts in southern regions (particularly on agriculture and public water supply) and sector-specific impacts in central and northern regions (e.g., on forestry or energy production). The protocol developed thus enabled a new and more comprehensive view on drought impacts across Europe. Related studies have already developed statistical techniques to evaluate the link between drought indices and the categorized impacts using EDII data. The EDII is a living database and is a promising source for further research on drought impacts, vulnerabilities, and risks across Europe. A key result is the extensive variety of impacts found across Europe and its documentation. This insight can therefore inform drought policy planning at national to international levels.

Abstract. The synoptic evolution and some meteorological impacts of the European winter storm Kyrill that swept across Western, Central, and Eastern Europe between 17 and 19 January 2007 are investigated. The intensity and large storm damage associated with Kyrill is explained based on synoptic and mesoscale environmental storm features, as well as on comparisons to previous storms. Kyrill appeared on weather maps over the US state of Arkansas about four days before it hit Europe. It underwent an explosive intensification over the Western North Atlantic Ocean while crossing a very intense zonal polar jet stream. A superposition of several favourable meteorological conditions west of the British Isles caused a further deepening of the storm when it started to affect Western Europe. Evidence is provided that a favourable alignment of three polar jet streaks and a dry air intrusion over the occlusion and cold fronts were causal factors in maintaining Kyrill's low pressure very far into Eastern Europe. Kyrill, like many other strong European winter storms, was embedded in a pre-existing, anomalously wide, north-south mean sea-level pressure (MSLP) gradient field. In addition to the range of gusts that might be expected from the synoptic-scale pressure field, mesoscale features associated with convective overturning at the cold front are suggested as the likely causes for the extremely damaging peak gusts observed at many lowland stations during the passage of Kyrill's cold front. Compared to other storms, Kyrill was by far not the most intense system in terms of core pressure and circulation anomaly. However, the system moved into a pre-existing strong MSLP gradient located over Central Europe which extended into Eastern Europe. This fact is considered determinant for the anomalously large area affected by Kyrill. Additionally, considerations of windiness in climate change simulations using two state-of-the-art regional climate models driven by ECHAM5 indicate that not only Central, but also Eastern Central Europe may be affected by higher surface wind speeds at the end of the 21st century. These changes are partially associated with the increased pressure gradient over Europe which is identified in the ECHAM5 simulations. Thus, with respect to the area affected, as well as to the synoptic and mesoscale storm features, it is proposed that Kyrill may serve as an interesting study case to assess future storm impacts.

Abstract. An algorithm developed to map flooded areas from synthetic aperture radar imagery is presented in this paper. It is conceived to be inserted in the operational flood management system of the Italian Civil Protection and can be used in an almost automatic mode or in an interactive mode, depending on the user's needs. The approach is based on the fuzzy logic that is used to integrate theoretical knowledge about the radar return from inundated areas taken into account by means of three electromagnetic scattering models, with simple hydraulic considerations and contextual information. This integration aims at allowing a user to cope with situations, such as the presence of vegetation in the flooded area, in which inundation mapping from satellite radars represents a difficult task. The algorithm is designed to work with radar data at L, C, and X frequency bands and employs also ancillary data, such as a land cover map and a digital elevation model. The flood mapping procedure is tested on an inundation that occurred in Albania on January 2010 using COSMO-SkyMed very high resolution X-band SAR data.

Tóm tắt. Quét laser mặt đất (TLS) cung cấp các đám mây điểm có độ phân giải cao về địa hình và các thiết bị TLS mới với phạm vi vượt quá 300 m hoặc thậm chí 1000 m là công cụ mạnh mẽ để mô tả và giám sát các chuyển động của sườn dốc. Nghiên cứu này tập trung vào sự lở đất Åknes có khối lượng 35 triệu m3 ở phía Tây Na Uy, đây là một trong những vụ lở đất được nghiên cứu và giám sát nhiều nhất trên thế giới. Các đám mây điểm TLS được sử dụng cho phân tích cấu trúc của vách đá chính dốc đứng, khó tiếp cận của vụ lở đất, bao gồm đánh giá các tập hợp gián đoạn và trục gập. Các số liệu TLS thu thập vào các năm 2006, 2007 và 2008 cung cấp thông tin về sự dịch chuyển 3-D cho toàn bộ khu vực quét và không bị hạn chế như các thiết bị khảo sát truyền thống chỉ đến các điểm đo đơn lẻ. Ma trận biến đổi affine giữa hai lần thu thập TLS miêu tả chính xác các dịch chuyển của vụ lở đất và cho phép tách biệt chúng thành các thành phần dịch chuyển dịch chuyển, chẳng hạn như tốc độ và hướng dịch chuyển, và các thành phần quay giống như lật ngược. Nghiên cứu này cho thấy khả năng của TLS trong việc thu được thông tin dịch chuyển 3-D đáng tin cậy trên một khu vực lớn không ổn định. Cuối cùng, một mô hình không ổn định khả thi cho phần trên của vụ lở đất Åknes giải thích các dịch chuyển dịch chuyển và quay đã đo được bằng sự kết hợp của trượt phẳng về phía nam dọc theo lớp gneiss, sự lún trọng lực theo chiều dọc dọc theo bề mặt trượt đáy phức tạp, bước và sự lật ngược về phía bắc theo cấu trúc graben đã mở.