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This is an advance summary of a forthcoming article in the Oxford Research Encyclopedia of Natural Hazard Science. Please check back later for the full article.
Natural disasters have increased dramatically in the twenty-first century. An estimated 217 million people are affected by natural disasters each year. Recent disasters, both nationally and globally, provide insight into how the degree of destruction and number of fatalities can negatively affect survivors. Cultural, political, and geographic factors may increase risk of trauma and negative mental health outcomes. Understanding these risks is critical to helping survivors recover in the aftermath of disasters. Different disasters pose different risks, and some communities are chronically affected. How to support these communities psychologically in the face of ongoing threats of destruction is an important question.
Recent years have also seen major advances in technology that provide new and innovative ways to manage disasters. Technological strategies can be harnessed to better serve the interests of disaster-affected communities. For example, warning times for disasters have increased because of better instrumentation and the ability to send messages sooner to communities that may be in the path of a disaster. These increased warning times may allow for psychological preparation before a disaster that can support positive mental health outcomes in recovery. Demands for evidence-based mental health interventions require an understanding of best practices in disaster response, challenges to past relief efforts, and the strategies and factors that can enhance effective future efforts.
Scott E. Robinson and Warren S. Eller
Natural hazards governance calls upon a diverse array of actors. The focus of most research—and most media coverage—has long been on governmental actors. Indeed, natural hazards governance relies on a complex arrangement of actors connected from the local, state, and national levels. Local organizations are the initial point of contact and face emerging threats. If the event exceeds the capacity of local organizations to respond, the governance system escalates the problem by expanding the participants to include state-level and, eventually, national-level actors. Natural hazards governance seeks to smooth and rationalize this process of escalation and expansion. Recent research has expanded this view to include nongovernmental actors like charitable organizations, religious institutions, and even private business. While charitable organizations have long been part of natural hazards governance, a broader range of charities, religious institutions, and private-sector companies has recently become more important to practice and scholarship. In many ways, the governance of these nongovernmental organizations resembles the structure of the governmental structure with its emphasis on escalation, expansion, and functional differentiation. Given the inclusion of so diverse a group of cooperating organizations, natural hazards governance faces notable challenges of communication, authority, and reliability.
Andrea Sarzynski and Paolo Cavaliere
Public participation in environmental management, and more specifically in hazard mitigation planning, has received much attention from scholars and practitioners. A shift in perspective now sees the public as a fundamental player in decision making rather than simply as the final recipient of a policy decision. Including the public in hazard mitigation planning brings widespread benefits. First, communities gain awareness of the risks they live with, and thus, this is an opportunity to empower communities and improve their resilience. Second, supported by a collaborative participation process, emergency managers and planners can achieve the ultimate goal of strong mitigation plans.
Although public participation is highly desired as an instrument to improve hazard mitigation planning, appropriate participation techniques are context dependent and some trade-offs exist in the process design (such as between representativeness and consensus building). Designing participation processes requires careful planning and an all-around consideration of the representativeness of stakeholders, timing, objectives, knowledge, and ultimately desired goals to achieve. Assessing participation also requires more consistent methods to facilitate policy learning from diverse experiences. New decision-support tools may be necessary to gain widespread participation from laypersons lacking technical knowledge of hazards and risks.
Ashley D. Ross
Public sector agencies at all levels of government work to mitigate risk, prepare for and respond to emergencies and disasters, and recover from catastrophic events. This action is guided by a national emergency management system that has evolved over time and was most recently reformed post-Hurricane Katrina. There is an extensive set of federal guidelines by the Department of Homeland Security and the Federal Emergency Management Agency that serve to structure the national system of hazard management. These include: the National Preparedness Goal; the National Preparedness System; National Planning Frameworks and accompanying Federal Interagency Operational Plans (FIOPs); the National Preparedness Report; and the Campaign to Build and Sustain Preparedness. Despite the considerable institutional and administrative guidance, there remain critical gaps in public-agency natural hazard management. These include lack of quality planning on the subnational level, insufficient local fiscal and human capital, and inconsistent regulation of the recovery process. While stricter implementation of federal mandates may partly address some of these issues, others will require greater political will in order to enact zoning regulations, create a shift in the acceptance of risk, and ensure that solutions are afforded by partnerships between civil, economic, and public entities.
Humankind has always lived with natural hazards and their consequences. While the frequency and intensity of geological processes may have remained relatively stable, population growth and infrastructure development in areas susceptible to experiencing natural hazards has increased societal risk and the losses experienced from hazard activity. Furthermore, increases in weather-related (e.g., hurricanes, wildfires) hazards emanating from climate change will increase risk in some countries and result in others having to deal with natural hazard risk for the first time.
Faced with growing and enduring risk, disaster risk reduction (DRR) strategies will play increasingly important roles in facilitating societal sustainability. This article discusses how readiness or preparedness makes an important contribution to comprehensive DRR. Readiness is defined here in terms of those factors that facilitate people’s individual and collective capability to anticipate, cope with, adapt to, and recover from hazard consequences. This article first discusses the need to conceptualize readiness as comprising several functional categories (structural, survival/direct action, psychological, community/capacity building, livelihood and community-agency readiness).
Next, the article discusses how the nature and extent of people’s readiness is a function of the interaction between the information available and the personal, family, community and societal factors used to interpret information and support readiness decision-making. The health belief model (HBM), protection motivation theory (PMT), person-relative-to-event (PrE) theory, theory of planned behavior (TPB), critical awareness (CA), protective action decision model (PADM), and community engagement theory (CET) are used to introduce variables that inform people’s readiness decision-making. A need to consider readiness as a developmental process is discussed and identifies how the variables introduced in the above theories play different roles at different stages in the development of comprehensive readiness.
Because many societies must learn to coexist with several sources of hazard, an “all-hazards” approach is required to facilitate the capacity of societies and their members to be resilient in the face of the various hazard consequences they may have to contend with. This article discusses research into readiness for the consequences that arise from earthquake, volcanic, flood, hurricane, and tornado hazards. Furthermore, because hazards transcend national and cultural divides, a comprehensive conceptualization of readiness must accommodate a cross-cultural perspective. Issues in the cross-cultural testing of theory is discussed, as is the need for further work into the relationship between readiness and culture-specific beliefs and processes.
Jonathan J. Gourley and Robert A. Clark III
Flash floods are one of the world’s deadliest and costliest weather-related natural hazards. In the United States alone, they account for an average of approximately 80 fatalities per year. Damages to crops and infrastructure are particularly costly. In 2015 alone, flash floods accounted for over $2 billion of losses; this was nearly half the total cost of damage caused by all weather hazards. Flash floods can be either pluvial or fluvial, but their occurrence is primarily driven by intense rainfall. Predicting the specific locations and times of flash floods requires a multidisciplinary approach because the severity of the impact depends on meteorological factors, surface hydrologic preconditions and controls, spatial patterns of sensitive infrastructure, and the dynamics describing how society is using or occupying the infrastructure.
Real-time flash flood forecasting systems rely on the observations and/or forecasts of rainfall, preexisting soil moisture and river-stage states, and geomorphological characteristics of the land surface and subsurface. The design of the forecast systems varies across the world in terms of their forcing, methodology, forecast horizon, and temporal and spatial scales. Their diversity can be attributed at least partially to the availability of observing systems and numerical weather prediction models that provide information at relevant scales regarding the location, timing, and severity of impending flash floods. In the United States, the National Weather Service (NWS) has relied upon the flash flood guidance (FFG) approach for decades. This is an inverse method in which a hydrologic model is run under differing rainfall scenarios until flooding conditions are reached. Forecasters then monitor observations and forecasts of rainfall and issue warnings to the public and local emergency management communities when the rainfall amounts approach or exceed FFG thresholds. This technique has been expanded to other countries throughout the world. Another approach, used in Europe, relies on model forecasts of heavy rainfall, where anomalous conditions are identified through comparison of the forecast cumulative rainfall (in space and time) with a 20-year archive of prior forecasts. Finally, explicit forecasts of flash flooding are generated in real time across the United States based on estimates of rainfall from a national network of weather radar systems.
Guy J.-P. Schumann
For about 40 years, with a proliferation over the last two decades, remote sensing data, primarily in the form of satellite and airborne imagery and altimetry, have been used to study floods, floodplain inundation, and river hydrodynamics. The sensors and data processing techniques that exist to derive information about floods are numerous. Instruments that record flood events may operate in the visible, thermal, and microwave range of the electromagnetic spectrum. Due to the limitations posed by adverse weather conditions during flood events, radar (microwave range) sensors are invaluable for monitoring floods; however, if a visible image of flooding can be acquired, retrieving useful information from this is often more straightforward. During recent years, scientific contributions in the field of remote sensing of floods have increased considerably, and science has presented innovative research and methods for retrieving information content from multi-scale coverages of disastrous flood events all over the world. Progress has been transformative, and the information obtained from remote sensing of floods is becoming mature enough to not only be integrated with computer simulations of flooding to allow better prediction, but also to assist flood response agencies in their operations.
Furthermore, this advancement has led to a number of recent and upcoming satellite missions that are already transforming current procedures and operations in flood modeling and monitoring, as well as our understanding of river and floodplain hydrodynamics globally. Global initiatives that utilize remote sensing data to strengthen support in managing and responding to flood disasters (e.g., The International Charter, The Dartmouth Flood Observatory, CEOS, NASA’s Servir and the European Space Agency’s Tiger-Net initiatives), primarily in developing nations, are becoming established and also recognized by many nations that are in need of assistance because traditional ground-based monitoring systems are sparse and in decline. The value remote sensing can offer is growing rapidly, and the challenge now lies in ensuring sustainable and interoperable use as well as optimized distribution of remote sensing products and services for science as well as operational assistance.
Mahesh Prakash, James Hilton, Claire Miller, Vincent Lemiale, Raymond Cohen, and Yunze Wang
Remotely sensed data for the observation and analysis of natural hazards is becoming increasingly commonplace and accessible. Furthermore, the accuracy and coverage of such data is rapidly improving. In parallel with this growth are ongoing developments in computational methods to store, process, and analyze these data for a variety of geospatial needs. One such use of this geospatial data is for input and calibration for the modeling of natural hazards, such as the spread of wildfires, flooding, tidal inundation, and landslides. Computational models for natural hazards show increasing real-world applicability, and it is only recently that the full potential of using remotely sensed data in these models is being understood and investigated. Some examples of geospatial data required for natural hazard modeling include:
• elevation models derived from RADAR and Light Detection and Ranging (LIDAR) techniques for flooding, landslide, and wildfire spread models
• accurate vertical datum calculations from geodetic measurements for flooding and tidal inundation models
• multispectral imaging techniques to provide land cover information for fuel types in wildfire models or roughness maps for flood inundation studies
Accurate modeling of such natural hazards allows a qualitative and quantitative estimate of risks associated with such events. With increasing spatial and temporal resolution, there is also an opportunity to investigate further value-added usage of remotely sensed data in the disaster modeling context. Improving spatial data resolution allows greater fidelity in models allowing, for example, the impact of fires or flooding on individual households to be determined. Improving temporal data allows short and long-term trends to be incorporated into models, such as the changing conditions through a fire season or the changing depth and meander of a water channel.
Abhilash Panda and Dilanthi Amaratunga
In 1990, 43% (2.3 billion) of the world’s population lived in urban areas, and by 2014 this percentage was at 54%. The urban population exceeded the rural population for the first time in 2008, and by 2050 it is predicted that urbanization will rise to 70% (see Albrito, “Making cities resilient: Increasing resilience to disasters at the local level,” Journal of Business Continuity & Emergency Planning, 2012). However, this increase in urban population has not been evenly spread throughout the world. As the urban population increases, the land area occupied by cities has increased at an even higher rate. It has been projected that by 2030, the urban population of developing countries will double, while the area covered by cities will triple (see United Nations, Department of Economic and Social Affairs, “World Urbanization Prospects: The 2014 Revision”). This emphasizes the need for resilience in the urban environment to anticipate and respond to disasters. Realizing this need, many local and international organizations have developed tools and frameworks to assist governments to plan and implement disaster risk reduction strategies efficiently. Sendai Framework’s Priorities for Action, Making Cities Resilient: My City is Getting Ready, and UNISDR’s Disaster Resilience Scorecard for Cities are major documents that provide essential guidelines for urban resilience. Given that, the disaster governance also needs to be efficient with ground-level participation for the implementation of these frameworks. This can be reinforced by adequate financing and resources depending on the exposure and risk of disasters. In essence, the resilience of a city is the resistance, coping capacity, recovery, adaptive capacity, and responsibility of everyone.
The management of natural hazards is undergoing considerable transformation, including the establishment of risk-based management approaches, the encouragement to govern natural hazards more inclusively, and the rising relevance of the concept of resilience. The benefits of this transformation are usually framed like this: Risk-based approaches are regarded as a rational way of balancing the costs associated with mitigating the consequences of hazards and the anticipated benefits; inclusive modes of governing risks help to increase the acceptance and quality of management processes as well as their outcomes; and the concept of resilience is connoted positively since it demands a greater openness to uncertainties and aims at increasing the capacities of various actors to cope with radical surprises.
However, the increasing consideration of both concepts in policy and decision-making processes is associated with a changing demarcation between public and private responsibilities and with an altering relationship between organizations involved in the management process and the wider public. To understand some of these dynamics, this contribution undertakes a change of perspective throughout its development: Instead of asking how the concepts of risk or resilience might be useful to improve the management and governance of natural hazards, one must understand how societies, particularly with regard to their handling of risks and hazards, are governed through the concepts of risk and resilience.
Following this perspective, risk-based management approaches have a defensive function in deflecting blame and rationalizing policy choices ex-ante by enabling managing organizations to more clearly define which risks they are responsible for (i.e., non-acceptable risks) and which are beyond their responsibility (i.e., acceptable risks). This demarcation also has profound distributional effects as acceptable risks usually need to be mitigated individually, raising the question of how to ensure the just sharing of the differently distributed benefits and burdens of risk-based approaches.
The concept of resilience in this context plays a paradoxical yet complementary role: In its more operational interpretation (e.g., adaptive management), resilience-based management approaches can be in conflict with risk-based approaches as they require those responsible for managing risks to follow antagonistic goals. While the idea of resilience puts an emphasis on openness and flexibility, risk-based approaches try to ensure proportionality by transforming uncertainties into calculable risks. At the same time, resilience-based governance approaches, with their emphasis on self-organization and learning, complement risk-based approaches in the sense that actors or communities that are exposed to “acceptable risks” are implicitly or explicitly made responsible for maintaining their own resilience, whereas the role of public authorities is usually restricted to an enabling one.
Maria Papathoma-Köhle and Dale Dominey-Howes
The second priority of the Sendai Framework for Disaster Risk Reduction 2015–2030 stresses that, to efficiently manage risk posed by natural hazards, disaster risk governance should be strengthened for all phases of the disaster cycle. Disaster management should be based on adequate strategies and plans, guidance, and inter-sector coordination and communication, as well as the participation and inclusion of all relevant stakeholders—including the general public. Natural hazards that occur with limited-notice or no-notice (LNN) challenge these efforts.
Different types of natural hazards present different challenges to societies in the Global North and the Global South in terms of detection, monitoring, and early warning (and then response and recovery). For example, some natural hazards occur suddenly with little or no warning (e.g., earthquakes, landslides, tsunamis, snow avalanches, flash floods, etc.) whereas others are slow onset (e.g., drought and desertification). Natural hazards such as hurricanes, volcanic eruptions, and floods may unfold at a pace that affords decision-makers and emergency managers enough time to affect warnings and to undertake preparedness and mitigative activities. Others do not. Detection and monitoring technologies (e.g., seismometers, stream gauges, meteorological forecasting equipment) and early warning systems (e.g., The Australian Tsunami Warning System) have been developed for a number of natural hazard types. However, their reliability and effectiveness vary with the phenomenon and its location. For example, tsunamis generated by submarine landslides occur without notice, generally rendering tsunami-warning systems inadequate.
Where warnings are unreliable or mis-timed, there are serious implications for risk governance processes and practices. To assist in the management of LNN events, we suggest emphasis should be given to the preparedness and mitigation phases of the disaster cycle, and in particular, to efforts to engage and educate the public. Risk and vulnerability assessment is also of paramount importance. The identification of especially vulnerable groups, appropriate land use planning, and the introduction and enforcement of building codes and reinforcement regulations, can all help to reduce casualties and damage to the built environment caused by unexpected events. Moreover, emergency plans have to adapt accordingly as they may differ from the evacuation plans for events with a longer lead-time. Risk transfer mechanisms, such as insurance, and public-private partnerships should be strengthened, and redevelopment should consider relocation and reinforcement of new buildings. Finally, participation by relevant stakeholders is a key concept for the management of LNN events as it is also a central component for efficient risk governance. All relevant stakeholders should be identified and included in decisions and their implementation, supported by good communication before, during, and after natural hazard events.
The implications for risk governance of a number of natural hazards are presented and illustrated with examples from different countries from the Global North and the Global South.
Rock avalanches are very large (greater than about 1 million m3) landslides from rock slopes, which can travel much farther than smaller events; the larger the avalanche, the greater the travel distance. Rock avalanches first became recognized in Switzerland in the 19th century, when the Elm and Goldau events killed many people a surprisingly long way from the origin of the landslide; these events first posed the “long-runout rock-avalanche” problem. In essence, the several-kilometer-long runout of these events appears to require low friction beneath and within the moving rock mass in order to explain their extremely long deposits, but in spite of intense research in recent decades this phenomenon still lacks a generally accepted explanation. Large collapses of volcano edifices can also generate rock avalanches that travel very long distances, albeit with a different runout–volume relationship to that of non-volcanic events. Even more intriguing is the presence of long-runout deposits not just on land but also beneath the sea and on the surfaces of Mars and the Moon.
Numerous studies of rock avalanches have revealed a number of consistencies in deposit and behavioral characteristics: for example, that little or no mixing of material occurs within the moving debris mass during runout; that the deposit material beneath a meter-scale surface layer is pervasively and intensely fragmented, with fragments down to submicrometer size; that many of these fragments are agglomerates of even finer particles; that throughout the travel of a rock avalanche large volumes of fine dust are produced; that rock avalanche surfaces are typically covered by hummocks of a range of sizes; and that, as noted above, runout distance increases with volume. Since rock avalanches can travel tens of kilometers from their source, they pose severe, if low-probability, direct hazards to societal assets in mountain valleys; in addition, they can trigger extensive and long-duration geomorphic hazard cascades.
Although large rock avalanches are rare (e.g., in a 10,000 km2 area of the Southern Alps in New Zealand, research showed that events larger than 5 × 107 m3 occurred about once every century), studies to date show that the proportion of total landslide volume involved in such large events is greater than the proportion in smaller, more frequent events, so that a large proportion of the total sediment generated in mountains by uplift and denudation originates in large rock avalanches. Consequently, large rock avalanches exert a significant influence on mountain geomorphology, for example by blocking rivers and forming landslide dams; these either fail, causing large dam-break floods and long-duration aggradation episodes to propagate down river systems, or remain intact to infill with sediment and form large valley flats. Rock avalanches that fall onto glaciers often result in large terminal moraines being formed as debris accumulates at the glacier terminus, and these moraines may have no relation to any climatic change. In addition, misinterpretation of rock avalanche deposits as moraines can cause underestimation of hazard risk and misinterpretation of paleoclimate.
Rock avalanche runout behavior poses fundamental scientific questions, and rock avalanches have important effects on a wide range of geomorphic processes, which in turn pose threats to society. Better understanding of these impressive and intriguing events is crucial for both geoscientific progress and for reducing impacts of future disasters.
Flood Risk Management (FRM) calls for stakeholders from multiple technical and social spheres to plan and implement policies and actions to manage flooding successfully. To work effectively across boundaries of knowledge, practice, priority, scale, institutions, and language created by such interdisciplinary or inter-stakeholder work, it is often necessary to employ intermediaries to create communication pathways between groups and spaces.
Intermediaries (also sometimes referred to as mediators or boundary spanners) are responsible for managing boundaries in such a way that multiple actors are able to communicate effectively with limited ambiguity or frustration. Sometimes, intermediaries enable two actors to come together who would usually not interact. For FRM, knowledge and experiences should ideally be brought together collaboratively and smoothly, whilst accounting for the diversity of perspectives and priorities between stakeholders involved.
Intermediaries may be organizations of humans, e.g., a public communications department; or objects, e.g., a computer model, website, or maps. Recognizing the utility of objects as intermediaries is important for understanding the multiplicity of mechanisms used to communicate FRM between experts and nonspecialist publics.
Charting how intermediaries bridge different boundaries, we see the diversity and utility of their work. Inspecting the construction of boundary objects as intermediaries allows the actors involved in their creation and definition to be identified and analyzed. This is important as it may contribute an understanding of how just and representative FRM decision making is.
Since the 1980s, various academic literatures from science and technology studies (STS) to organizational studies have addressed the role of intermediaries and mediators, particularly in relation to business management, computer sciences, and biomedicine. However, in FRM where risk analysis and communication is king, discussing how to manage pertinent and credible transboundary information is also important.
Jonatan A. Lassa
The collaborative disaster risk governance framework promises better collaboration between governments, the private sector, civil society, academia, and communities at risks. In the context of modern disaster risk reduction systems, the key triadic institutions, namely government (state), the private sector (business/market), and NGOs (civil society), have been gradually transforming their ecosystem to utilize more proactive disaster response strategies, equipped with professional staff and technical experts and armed with social and humanitarian imperatives to reduce the risks of disasters. While the roles of governments and public actions have received greater attention in disaster and emergency management studies, recent shifts in attention to promote bolder engagements of both non-governmental organizations and business communities in risk reduction can be seen as a necessary condition for the future resilience of society.
Historically speaking, NGOs have exercised models of moral imperative whereby they build their relevancy and legitimacy to address gaps and problems at global and local levels. NGOs have been part of the global disaster risk reduction (DRR) ecosystem as they continue to shape both humanitarian emergencies action and the DRR agenda at different levels where their presence is needed and valued and their contribution is uniquely recognized. This article exemplifies the roles of NGOs at different levels and arenas ranging from local to international disaster risk reduction during the last 70 years, especially since World War II. It also provides examples of potential roles of NGOs under the Sendai Framework for Disaster Risk Reduction 2030.
Recent extreme hydrological events (e.g., in the United States in 2005 or 2012, Pakistan in 2010, and Thailand in 2011) revealed increasing flood risks due to climate and societal change. Consequently, the roles of multiple stakeholders in flood risk management have transformed significantly. A central aspect here is the question of sharing responsibilities among global, national, regional, and local stakeholders in organizing flood risk management of all kinds. This new policy agenda of sharing responsibilities strives to delegate responsibilities and costs from the central government to local authorities, and from public administration to private citizens. The main reasons for this decentralization are that local authorities can deal more efficiently with public administration tasks concerned with risks and emergency management. Resulting locally based strategies for risk reduction are expected to tighten the feedback loops between complex environmental dynamics and human decision-making processes. However, there are a series of consequences to this rescaling process in flood risk management, regarding the development of new governance structures and institutions, like resilience teams or flood action groups in the United Kingdom. Additionally, downscaling to local-level tasks without additional resources is particularly challenging. This development has tightened further with fiscal and administrative cuts around the world resulting from the global economic crisis of 2007–2008, which tightening eventually causes budget restrictions for flood risk management. Managing local risks easily exceeds the technical and budgetary capacities of municipal institutions, and individual citizens struggle to carry the full responsibility of flood protection. To manage community engagement in flood risk management, emphasis should be given to the development of multi-level governance structures, so that multiple stakeholders share fairly the power, resources, and responsibility in disaster planning. If we fail to do so, some consequences would be: (1), “hollowing out” the government, including the downscaling of the responsibility towards local stakeholders; and (2), inability of the government to deal with the new tasks due to lack of resources transferred to local authorities.
Prediction of floods at locations where no streamflow data exist is a global issue because most of the countries involved don’t have adequate streamflow records. The United States Geological Survey developed the regional flood frequency (RFF) analysis to predict annual peak flow quantiles, for example, the 100-year flood, in ungauged basins. RFF equations are pure statistical characterizations that use historical streamflow records and the concept of “homogeneous regions.” To supplement the accuracy of flood quantile estimates due to limited record lengths, a physical solution is required. It is further reinforced by the need to predict potential impacts of a changing hydro-climate system on flood frequencies. A nonlinear geophysical theory of floods, or a scaling theory for short, focused on river basins and abandoned the “homogeneous regions” concept in order to incorporate flood producing physical processes. Self-similarity in channel networks plays a foundational role in understanding the observed scaling, or power law relations, between peak flows and drainage areas. Scaling theory of floods offers a unified framework to predict floods in rainfall-runoff (RF-RO) events and in annual peak flow quantiles in ungauged basins.
Theoretical research in the course of time clarified several key ideas: (1) to understand scaling in annual peak flow quantiles in terms of physical processes, it was necessary to consider scaling in individual RF-RO events; (2) a unique partitioning of a drainage basin into hillslopes and channel links is necessary; (3) a continuity equation in terms of link storage and discharge was developed for a link-hillslope pair (to complete the mathematical specification, another equation for a channel link involving storage and discharge can be written that gives the continuity equation in terms of discharge); (4) the self-similarity in channel networks plays a pivotal role in solving the continuity equation, which produces scaling in peak flows as drainage area goes to infinity (scaling is an emergent property that was shown to hold for an idealized case study); (5) a theory of hydraulic-geometry in channel networks is summarized; and (6) highlights of a theory of biological diversity in riparian vegetation along a network are given.
The first observational study in the Goodwin Creek Experimental Watershed, Mississippi, discovered that the scaling slopes and intercepts vary from one RF-RO event to the next. Subsequently, diagnostic studies of this variability showed that it is a reflection of variability in the flood-producing mechanisms. It has led to developing a model that links the scaling in RF-RO events with the annual peak flow quantiles featured here.
Rainfall-runoff models in engineering practice use a variety of techniques to calibrate their parameters using observed streamflow hydrographs. In ungagged basins, streamflow data are not available, and in a changing climate, the reliability of historic data becomes questionable, so calibration of parameters is not a viable option. Recent progress on developing a suitable theoretical framework to test RF-RO model parameterizations without calibration is briefly reviewed.
Contributions to generalizing the scaling theory of floods to medium and large river basins spanning different climates are reviewed. Two studies that have focused on understanding floods at the scale of the entire planet Earth are cited.
Finally, two case studies on the innovative applications of the scaling framework to practical hydrologic engineering problems are highlighted. They include real-time flood forecasting and the effect of spatially distributed small dams in a river network on real-time flood forecasting.
Sinkholes or dolines are closed depressions characteristic of terrains underlain by soluble rocks (carbonates and/or evaporites). They may be related to the differential dissolutional lowering of the ground surface (solution sinkholes) or to subsidence induced by subsurface karstification (subsidence sinkholes). Three main subsidence mechanisms may operate individually or in combination: collapse, sagging, and suffosion. Subsidence sinkholes may cause severe damage to human built structures, and the occurrence of catastrophic collapse sinkholes may lead to the loss of human life. Dissolution and subsidence processes involved in the development of subsidence sinkholes are controlled by a wide range of natural and anthropogenic factors. Recent literature reviews reveal that the vast majority of the damaging sinkholes are induced by human activities (e.g., water table decline, water input to the ground). The main steps in sinkhole hazard and risk assessment include: (a) construction of comprehensive sinkhole inventories and detailed sinkhole characterization; (b) development of independently tested sinkhole susceptibility and hazard models, preferably incorporating magnitude and frequency relationships; (c) assessing risk combining hazard and vulnerability data. Sinkhole risk models may be used as the basis to perform cost-benefit analyses that allow the cost-effectiveness of different mitigation strategies to be estimated. Three main concepts may be applied to reduce sinkhole risk: (a) avoiding sinkholes and sinkhole-prone areas (preventive planning); (b) diminishing the activity of dissolution and/or subsidence processes (hazard reduction); (c) incorporating special designs in the structures (vulnerability reduction). Although our capabilities to investigate sinkhole hazards and reduce the associated risks will continue to increase in the near future, the damage related to sinkholes will also increase, largely due to the adverse changes caused by human activities on the karst environments and the ineffective knowledge transfer between scientists, technicians, and decision-makers. This article presents the processes and factors involved in sinkhole development and reviews the main approaches used to assess and manage sinkhole hazards and risks.
Avalanches have long been a natural threat to humans in mountainous areas. At the end of the Middle Ages, the population in Europe experienced significant growth, leading to an intensive exploitation of upper valleys. At almost the same time, Europe’s climate cooled down considerably and severe winters became more common. In the Alps, several villages were partly destroyed by avalanches, forcing inhabitants to develop the first mitigation strategies against the threat. By the late 19th century, the development of central administrations led to the creation of national forestry departments in each alpine country, principally to tackle the dangers posed by avalanches. As a result, forest engineers conceived not only the science of avalanches but also the first large-scale techniques to alleviate avalanche risks (such as reforestation). However, with the steady growth of transport, industry, tourism, and urbanization in high-altitude areas, these earlier measures soon reached their limits. A new impetus was then given to better forecasting avalanche activity and predicting the destructive potential of extreme avalanches. Avalanche zoning, snowfall forecasts, avalanche-dynamics models, and new protection systems for the protection of structures and inhabitants have become increasingly more common since World War II.
With the advent of personal computers and the increasing sophistication of computational resources, it has become easier to predict the behavior of avalanches and protect threatened areas accordingly. The success of this research and the protection policies implemented since World War II are reflected in the drastic reduction in the number of disasters affecting dwellings in the Alps (most deaths by avalanche now occur during recreational activities). Significant progress has been made since the 1980s, leading to a better understanding of avalanche behavior and the mediation of associated risks. Yet we should not assume that this progress is steady or that our capacity to control such hazards is more advanced than it was two decades ago. Efforts to predict avalanches contrast with work in other sciences such as meteorology, for which forecasts have become increasingly more reliable with advancements in computational power. Explaining the difference is simple: in meteorology, the material is air, a substance whose behavior is well known. The main difficulty lies in the computation of enormous volumes of air encountering various flow and temperature conditions. For avalanches, the material is snow, a subtle mixture of water (in different forms) and air, whose behavior is remarkably complex. Modern models of avalanche dynamics are able to predict this behavior with varying degrees of success.
Daniel P. Aldrich, Michelle A. Meyer, and Courtney M. Page-Tan
The impact of disasters continues to grow in the early 21st century, as extreme weather events become more frequent and population density in vulnerable coastal and inland cities increases. Against this backdrop of risk, decision-makers persist in focusing primarily on structural measures to reduce losses centered on physical infrastructure such as berms, seawalls, retrofitted buildings, and levees. Yet a growing body of research emphasizes that strengthening social infrastructure, not just physical infrastructure, serves as a cost-effective way to improve the ability of communities to withstand and rebound from disasters. Three distinct kinds of social connections, including bonding, bridging, and linking social ties, support resilience through increasing the provision of emergency information, mutual aid, and collective action within communities to address natural hazards before, during, and after disaster events. Investing in social capital fosters community resilience that transcends natural hazards and positively affects collective governance and community health.
Social capital has a long history in social science research and scholarship, particularly in how it has grown within various disciplines. Broadly, the term describes how social ties generate norms of reciprocity and trust, allow collective action, build solidarity, and foster information and resource flows among people. From education to crime, social capital has been shown to have positive impacts on individual and community outcomes, and research in natural hazards has similarly shown positive outcomes for individual and community resilience. Social capital also can foster negative outcomes, including exclusionary practices, corruption, and increased inequality. Understanding which types of social capital are most useful for increasing resilience is important to move the natural hazards field forward.
Many questions about social capital and natural hazards remain, at best, partially answered. Do different types of social capital matter at different stages of disaster—e.g., mitigation, preparedness, response, and recovery? How do social capital’s effects vary across cultural contexts and stratified groups? What measures of social capital are available to practitioners and scholars? What actions are available to decision-makers seeking to invest in the social infrastructure of communities vulnerable to natural hazards? Which programs and interventions have shown merit through field tests? What outcomes can decision-makers anticipate with these investments? Where can scholars find data sets on resilience and social capital? The current state of knowledge about social capital in disaster resilience provides guidance about supporting communities toward more resilience.
Philip Bubeck, Antje Otto, and Juergen Weichselgartner
Floods remain the most devastating natural hazard globally, despite substantial investments in flood prevention and management in recent decades. Fluvial floods, such as the ones in Pakistan in 2010 and Thailand in 2011, can affect entire countries and cause severe economic and human losses. Also, coastal floods can inflict substantial harm owing to their destructive forces in terms of wave and tidal energy. A flood type that received growing attention in recent years is flooding from pluvial events (heavy rainfall). Even though these are locally confined, their sudden onset and unpredictability pose a danger to areas that are generally not at risk from flooding. In the future, it is projected that flood risk will increase in many regions both because of the effects of global warming on the hydrological cycle and the continuing concentration of people and economic assets in risk-prone areas.
Floods have a large variety of societal impacts that span across space and time. While some of these impacts are obvious and have been well researched, others are more subtle and less is known about their complex processes and long-term effects. The most immediate and apparent impact of floods is direct damage caused by physical contact between floodwaters and economic assets, cultural heritage, or human beings, with the result for humans being injuries and deaths. Direct flood damage can amount to billions of US dollars for single events, such as the floods in the Danube and Elbe catchment in Central Europe in 2002 and 2013. More indirect economic implications are the losses that occur outside of the flood event in space and time, such as losses due to business disruption. The flood in Thailand in 2011, for instance, resulted in a lack of auto parts supplies and consequently the shutdown of car manufacturing within and outside the flood zone.
Floods also have long-term indirect impacts on flood-affected people and communities. Experiencing property damage and losing important personal belongings can have a negative psychological effect on flood victims. Much less is known about this type of flood impact: how long do these impacts last? What makes some people or communities recover faster than others from financial losses and emotional stress? Moreover, flood impacts are not equally distributed across different groups of society. Often, poor, elderly, and marginalized societal groups are particularly vulnerable to the effects of flooding inasmuch as these groups generally have little social, human, and financial coping capacities. In many countries, women regularly bear a disproportionately high burden because of their societal status.
Finally, severe floods often provide so-called windows of opportunities, enabling rapid policy change, resulting in new flood risk management policies. Such newly adopted policy arrangements can lead to societal conflicts over issues of interests, equity, and fairness. For instance, flood events often trigger large-scale investment in flood defense infrastructure, which are associated with high construction costs. Although these costs are usually borne by the taxpayer, often only a small proportion of society shares in their benefits. In addition, societal conflict can arise concerning where to build structural measures; what impacts these measures have on the ground regarding economic development potentials, different kinds of uses, and nature protection; and which effects are expected downstream. In such controversies, issues of participation and decision making are central and often highly contested.
While floods are usually associated with negative societal impacts in industrialized countries, they also have beneficial impacts on nature and society. In many parts of the world, the livelihood of millions of people depends on the recurring occurrence of flooding. For instance, farming communities in or near floodplains rely upon regular floodwaters that carry nutrients and sediments, enriching the soil and making it fertile for cultivation.