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The immediate aftermath of a great urban earthquake is a dramatic and terrible event, comparable to a massive terrorist attack. Yet the shocking impact soon fades from the public mind and receives surprisingly little attention from historians, unlike wars and human atrocities. In 1923, the Great Kanto earthquake and its subsequent fires demolished most of Tokyo and Yokohama and killed around 140,000 Japanese: a level of devastation and fatalities comparable with the atomic bombing of Hiroshima and Nagasaki in 1945. But the second event has infinitely more resonance in public consciousness and historical studies than the first. Indeed, most people would be challenged to name a single earthquake with an indisputable historical impact, including even the most famous of all earthquakes: the San Francisco earthquake and fire of 1906.
In truth, however, great earthquakes, from ancient times—as recorded by Greek and biblical writers—to the present day, have had major cultural, economic, and political consequences—often a combination of all three—some of which were beneficial. Thus, the current prime minister of India owes his election in 2014 to an earthquake that devastated part of his home state of Gujarat in 2001, which led to its striking economic growth. The martial law imposed on Tokyo and Yokohama after the 1923 earthquake gave new authority to the Japanese army, which eventually took over the Japanese government and led Japan to war with China and the world. The destruction of San Francisco in 1906 produced a boom in rebuilding and financial and technological development of the surrounding area on the San Andreas Fault, including what became Silicon Valley. A great earthquake in Venezuela in 1812 was the principal cause of the temporary defeat of its leader Simon Bolivar by the Spanish colonial regime, but his subsequent exile led to his permanent freeing of Bolivia, Colombia, Ecuador, Peru, and Venezuela from Spanish rule. The catastrophic Lisbon earthquake of 1755—as well known in the early 19th century as the 1945 atomic bombings are today—was a pivotal factor in the freeing of Enlightenment science from Catholic religious orthodoxy, as epitomized by Voltaire’s satirical novel Candide, written in response to the earthquake. Even the minor earthquakes in Britain in 1750, the so-called Year of Earthquakes, produced the earliest scientific understanding of earthquakes, published by the Royal Society: the beginning of seismology.
The long-term impact of a great earthquake depends on its epicenter, magnitude, and timing—and also on human factors: the political, social, intellectual, religious, and cultural resources specific to a region’s history. Each earthquake-struck society offers its own particular lesson, and yet, taken together, such earth-shattering events have important shared consequences for the history of the world.
Joanne Stevenson, Ilan Noy, Garry McDonald, Erica Seville, and John Vargo
The economics of disasters is a relatively new and emerging branch of economics. Advances made in analysis, including modeling the spatial economic impacts of disasters, is increasing our ability to project disaster outcomes and explore how to reduce their negative impacts. This work is supported by a growing body of case studies on the organizational and economic impacts of disasters, such as Chang’s in-depth analysis of the Port of Kobe’s decline following the 1995 Great Hanshin earthquake, and the evolving studies of the workforce trends during the ongoing recovery of Christchurch, New Zealand, following a series of earthquakes in 2010 and 2011.
The typical view of post-disaster economies depicts a pattern of destruction, renewal, and improvement. Evidence shows, however, that this pattern does not occur in all cases. The degree of economic disruption and the time it takes for different economies to recover varies significantly depending on characteristics such as literacy rates, institutional competency, per capita income, and government spending.
If the impacts are large relative to the national economy, a disaster can negatively affect the country or sub-national region’s fiscal position. Similarly, disasters may have significant implications for the national trade balance. If, for example, productive capacity is reduced by disaster damage, exports decrease, the trade balance may weaken, and localized inflation may increase.
Studies of individual, household, industry, and business responses to disasters (i.e., microeconomic analyses) cover a broad range of topics relevant to the choices actors make and their interactions with markets. Both household consumption and labor markets face expansion and contraction in areas affected by disasters, with increased consumption and employment often happening in reconstruction related industries.
Additionally, the ability of businesses to absorb, respond, and recover in the face of disasters varies widely. Characteristics such as size, number of locations, and pre-disaster financial health are positively correlated with successful business recovery. Businesses can minimize productivity disruptions and recapture lost productivity by conserving scarce inputs, utilizing inventories, and rescheduling production.
Assessing the progress of economic recovery and predicting future outcomes are important and complex challenges. Researchers use various methodologies to evaluate the effects of natural disasters at different scales of the economy. Surveys, microeconomic models, econometric models, input-output models, and computable general equilibrium models each offer different insights into the effect of disasters on economies.
The study of disaster economics still faces issues with consistency, comprehensiveness, and comparability. Yet, as the science continues to advance there is a growing cross-disciplinary accumulation of knowledge with real implications for policy and the private sector.
Evolution of Strategic Flood Risk Management in Support of Social Justice, Ecosystem Health, and Resilience
Throughout history, flood management practice has evolved in response to flood events. This heuristic approach has yielded some important incremental shifts in both policy and planning (from the need to plan at a catchment scale to the recognition that flooding arises from multiple sources and that defenses, no matter how reliable, fail). Progress, however, has been painfully slow and sporadic, but a new, more strategic, approach is now emerging.
A strategic approach does not, however, simply sustain an acceptable level of flood defence. Strategic Flood Risk Management (SFRM) is an approach that relies upon an adaptable portfolio of measures and policies to deliver outcomes that are socially just (when assessed against egalitarian, utilitarian, and Rawlsian principles), contribute positively to ecosystem services, and promote resilience. In doing so, SFRM offers a practical policy and planning framework to transform our understanding of risk and move toward a flood-resilient society. A strategic approach to flood management involves much more than simply reducing the chance of damage through the provision of “strong” structures and recognizes adaptive management as much more than simply “wait and see.” SFRM is inherently risk based and implemented through a continuous process of review and adaptation that seeks to actively manage future uncertainty, a characteristic that sets it apart from the linear flood defense planning paradigm based upon a more certain view of the future.
In doing so, SFRM accepts there is no silver bullet to flood issues and that people and economies cannot always be protected from flooding. It accepts flooding as an important ecosystem function and that a legitimate ecosystem service is its contribution to flood risk management. Perhaps most importantly, however, SFRM enables the inherent conflicts as well as opportunities that characterize flood management choices to be openly debated, priorities to be set, and difficult investment choices to be made.
Deserai A. Crow
As with countless other policy areas, natural hazard policy can be viewed as a jurisdictional competition between executive and legislative branches. While policymaking supremacy is delegated to the legislative branch in constitutional democracies, the power over implementation, budgeting, and grant-making that executive agencies enjoy means that the executive branch wields considerable influence over outcomes in natural hazards policymaking. The rules that govern federal implementation of complex legislative policies put the implementing agency at the center of influence over how policy priorities play out in local, county, and state processes before, during, and after disasters hit.
Examples abound related to this give-and-take between the legislative and executive functions of government within the hazards and disaster realm, but none more telling than the changes made to US disaster policy after September 11th, which profoundly affected natural hazards policy as well as security policy. The competition and potential for mismatch between legislative and executive priorities has been heightened since the Federal Emergency Management Agency (FEMA) was reorganized under the Department of Homeland Security. While this may appear uniquely American, the primacy of terrorism and other security-related threats not only dwarfs natural hazards issues in the United States, but also globally. Among the most professionalized and powerful natural hazards and disaster agencies prior to 9/11, FEMA has seen its influence diminished and its access to decision-makers reduced.
This picture of legislative and executive actors within the natural hazards policy domain who compete for supremacy goes beyond the role of FEMA and post-9/11 policy. Power dynamics associated with budgets, oversight and accountability, and relative power among executive agencies are ongoing issues important to understanding the competition for policy influence as natural hazards policy competes for attention, funding, and power within the broader domain of all-hazards policy.
Fatalism about natural disasters hinders action to prepare for those disasters, and overcoming this fatalism is one key element to preparing people for these disasters. Research by Bostrom and colleagues shows that failure to act often reflects gaps and misconceptions in citizen’s mental models of disasters. Research by McClure and colleagues shows that fatalistic attitudes reflect people’s attributing damage to uncontrollable natural causes rather than controllable human actions, such as preparation. Research shows which precise features of risk communications lead people to see damage as preventable and to attribute damage to controllable human actions. Messages that enhance the accuracy of mental models of disasters by including human factors recognized by experts lead to increased preparedness. Effective messages also communicate that major damage in disasters is often distinctive and reflects controllable causes. These messages underpin causal judgments that reduce fatalism and enhance preparation. Many of these messages are not only beneficial but also newsworthy. Messages that are logically equivalent but are differently framed have varying effects on risk judgments and preparedness. The causes of harm in disasters are often contested, because they often imply human responsibility for the outcomes and entail significant cost.
Charlotte L. Kirschner, Akheil Singla, and Angie Flick
As more and more of the population moves to areas prone to natural hazards, the costs of disasters are on the rise. Given that these events are an eventuality, governments must aid their communities in promoting disaster resilience, enabling their communities to reduce their susceptibility to natural hazards, and adapting to and recovering from disasters when they occur.
The federal system in the United States divides these responsibilities among national, state, and local governments. Local and state governments are largely responsible for the direct provision of services to their communities, and the Stafford Act of 1988 provides that the federal government will pay at least 75% of all eligible expenses once a presidential major disaster declaration has been made. As a result, state and local governments have become largely reliant on transfers from the federal government to pay for disaster relief and recovery efforts. This system encourages state and local governments to ignore the risks they face and turn to the federal government for aid after a disaster.
This system also seems to underemphasize an important mechanism that can bolster disaster resilience: financing the costs of disasters in advance through ex ante budgeting. Four tools for budgeting ex ante—intergovernmental grants, disaster stabilization funds, the municipal bond market, and hazard insurance—are described and examples of their use provided. Despite limited use by state governments, these tools provide governments the opportunity to build community resilience to disasters by budgeting ex ante for them.
Natural disasters cause massive social disruptions and can lead to tremendous economic and human losses. Given their uncertain and destructive nature, disasters invariably induce significant governmental responses and typically pose severe financial challenges for jurisdictions across all levels of government. From a public finance perspective, disasters cause governments to incur additional spending on various emergency management activities, and by disrupting normal business activities they also affect tax base robustness and cause revenue losses. The question is: How significant are these fiscal effects and how do they affect hazards governance more generally? Understanding the fiscal implications of natural disasters is essential to evaluating the size of the economic costs of disasters as well as forecasting governments’ financial exposure to future shocks. Furthermore, how disaster costs are shared among different levels of government is another important question concerning the intergovernmental dynamics of disaster management.
In the U.S. federal system, the direct fiscal costs of natural disasters (i.e., increased government expenditures due to disaster shocks) are largely borne by the federal government. It is estimated that Hurricane Katrina cost the federal government approximately $120 billion while Hurricane Sandy cost $60 billion. Even in the years without large-scale disaster events, federal disaster spending is between $2 billion and $6 billion annually. Under the Stafford Act, the federal government plays a critical role in funding disaster-related programs (e.g., direct relief, mitigation grants, and subsidized insurance programs) and redistributing the actual costs of natural hazards, meaning that a considerable portion of the local disaster burden is shifted to all U.S. taxpayers. This raises a set of issues concerning the equity and efficiency of the U.S. disaster policy framework.
Managing disasters involves multiphased activities to mitigate, prepare for, respond to, and recover from disaster shocks. There is a common belief that the federal government inappropriately spends far more on ex post disaster response, relief, and recovery than what it spends on ex ante mitigation and preparedness, often driven by political motivations (e.g., meeting voters’ preferences for postdisaster aid) and the current budget rules. As pointed out by many others, federal disaster relief and assistance distort the subnational incentive to invest in local disaster prevention and mitigation efforts. Furthermore, given the mounting evidence on the cost-effectiveness of disaster mitigation programs in reducing future disaster damages, the current practice of focusing resources on postdisaster assistance means substantial public welfare losses. In recent years there has been a call for the federal government to shift its disaster policy emphasis toward mitigation and preparedness and also to facilitate local efforts on mitigation. To achieve the goal requires a comprehensive reform in government budgeting for emergency management.
The rapid increase in losses from flooding underlines the importance of risk reduction efforts to prevent or at least mitigate the damaging impacts that floods can bring to communities, businesses, and countries. This article provides an overview of how the science of disaster risk management has improved understanding of pre-event risk reduction [or disaster risk reduction (DRR)]. Implementation, however, is still lagging, particularly when compared to expenditure for recovery and repair after a flood event. In response, flood insurance is increasingly being suggested as a potential lever for risk reduction, despite concerns about moral hazard. The article considers the literature that has emerged on this topic and discusses if the conceptual efforts of linking flood insurance and risk reduction have led to practical action. Overall, there is limited evidence of flood insurance effectively promoting risk reduction. To the extent there is, it suggests that more complex behavioral aspects are also at play. Further evidence is required to support this potential role, particularly around data and risk assessment, and the viability of different risk reduction measures.
David Proverbs and Jessica Lamond
Flood resilient construction has become an essential component of the integrated approach to flood risk management, now widely accepted through the concepts of making space for water and living with floods. Resilient construction has been in place for centuries, but only fairly recently has it been recognized as part of this wider strategy to manage flood risk. Buildings and the wider built environment are known to play a key role in flood risk management, and when buildings are constructed on or near to flood plains there is an obvious need to protect these. Engineered flood defense systems date back centuries, with early examples seen in China and Egypt. Levees were first built in the United States some 150 years ago, and were followed by the development of flood control acts and regulations. In 1945, Gilbert Fowler White, the so-called “father of floodplain management,” published his influential thesis which criticized the reliance on engineered flood defenses and began to change these approaches. In Europe, a shortage of farmable land led to the use of land reclamation schemes and the ensuing Land Drainage acts before massive flood events in the mid-20th century led to a shift in thinking towards the engineered defense schemes such as the Thames Barrier and Dutch dyke systems. The early 21st century witnessed the emergence of the “living with water” philosophy, which has resulted in the renewed understanding of flood resilience at a property level.
The scientific study of construction methods and building technologies that are robust to flooding is a fairly recent phenomenon. There are a number of underlying reasons for this, but the change in flood risk philosophy coupled with the experience of flood events and the long process of recovery is helping to drive research and investment in this area. This has led to a more sophisticated understanding of the approaches to avoiding damage at an individual property level, categorized under three strategies, namely avoidance technology, water exclusion technology, and water entry technology. As interest and policy has shifted to water entry approaches, alongside this has been the development of research into flood resilient materials and repair and reinstatement processes, the latter gaining much attention in the recognition that experience will prompt resilient responses and that the point of reinstatement provides a good opportunity to install resilient measures.
State-of-the-art practices now center on avoidance strategies incorporating planning legislation in many regions to prohibit or restrict new development in flood plains. Where development pressures mean that new buildings are permitted, there is now a body of knowledge around the impact of flooding on buildings and flood resilient construction and techniques. However, due to the variety and complexity of architecture and construction styles and varying flood risk exposure, there remain many gaps in our understanding, leading to the use of trial and error and other pragmatic approaches. Some examples of avoidance strategies include the use of earthworks, floating houses, and raised construction.
The concept of property level flood resilience is an emerging concept in the United Kingdom and recognizes that in some cases a hybrid approach might be favored in which the amount of water entering a property is limited, together with the likely damage that is caused. The technology and understanding is moving forward with a greater appreciation of the benefits from combining strategies and property level measures, incorporating water resistant and resilient materials. The process of resilient repair and considerate reinstatement is another emerging feature, recognizing that there will be a need to dry, clean, and repair flood-affected buildings. The importance of effective and timely drying of properties, including the need to use materials that dry rapidly and are easy to decontaminate, has become more apparent and is gaining attention.
Future developments are likely to concentrate on promoting the uptake of flood resilient materials and technologies both in the construction of new and in the retrofit and adaptation of existing properties. Further development of flood resilience technology that enhances the aesthetic appeal of adapted property would support the uptake of measures. Developments that reduce cost or that offer other aesthetic or functional advantages may also reduce the barriers to uptake. A greater understanding of performance standards for resilient materials will help provide confidence in such measures and support uptake, while further research around the breathability of materials and concerns around mold and the need to avoid creating moisture issues inside properties represent some of the key areas.
Floods affect more people worldwide than any other natural hazard. Flood risk results from the interplay of a range of processes. For river floods, these are the flood-triggering processes in the atmosphere, runoff generation in the catchment, flood waves traveling through the river network, possibly flood defense failure, and finally, inundation and damage processes in the flooded areas. In addition, ripple effects, such as regional or even global supply chain disruptions, may occur.
Effective and efficient flood risk management requires understanding and quantifying the flood risk and its possible future developments. Hence, risk analysis is a key element of flood risk management. Risk assessments can be structured according to three questions: What can go wrong? How likely is it that it will happen? If it goes wrong, what are the consequences? Before answering these questions, the system boundaries, the processes to be included, and the detail of the analysis need to be carefully selected.
One of the greatest challenges in flood risk analyses is the identification of the set of failure or damage scenarios. Often, extreme events beyond the experience of the analyst are missing, which may bias the risk estimate. Another challenge is the estimation of probabilities. There are at most a few observed events where data on the flood situation, such as inundation extent, depth, and loss are available. That means that even in the most optimistic situation there are only a few data points to validate the risk estimates. The situation is even more delicate when the risk has to be quantified for important infrastructure objects, such as breaching of a large dam or flooding of a nuclear power plant. Such events are practically unrepeatable. Hence, estimating of probabilities needs to be based on all available evidence, using observations whenever possible, but also including theoretical knowledge, modeling, specific investigations, experience, or expert judgment. As a result, flood risk assessments are often associated with large uncertainties. Examples abound where authorities, people at risk, and disaster management have been taken by surprise due to unexpected failure scenarios. This is not only a consequence of the complexity of flood risk systems, but may also be attributed to cognitive biases, such as being overconfident in the risk assessment. Hence, it is essential to ask: How wrong can the risk analysis be and still guarantee that the outcome is acceptable?
Dennis John Parker
Humankind is becoming increasingly dependent on timely flood warnings. Dependence is being driven by an increasing frequency and intensity of heavy rainfall events, a growing number of disruptive and damaging floods, and rising sea levels associated with climate change. At the same time, the population living in flood-risk areas and the value of urban and rural assets exposed to floods are growing rapidly. Flood warnings are an important means of adapting to growing flood risk and learning to live with it by avoiding damage, loss of life, and injury. Such warnings are increasingly being employed in combination with other flood-risk management measures, including large-scale mobile flood barriers and property-level protection measures.
Given that lives may well depend on effective flood warnings and appropriate warning responses, it is crucial that the warnings perform satisfactorily, particularly by being accurate, reliable, and timely. A sufficiently long warning lead time to allow precautions to be taken and property and people to be moved out of harm’s way is particularly important. However, flood warnings are heavily dependent on the other components of flood forecasting, warning, and response systems of which they are a central part. These other components—flood detection, flood forecasting, warning communication, and warning response—form a system that is characterized as a chain, each link of which depends on the other links for effective outcomes. Inherent weaknesses exist in chainlike processes and are often the basis of warning underperformance when it occurs.
A number of key issues confront those seeking to create and successfully operate flood warning systems, including (1) translating technical flood forecasts into warnings that are readily understandable by the public; (2) taking legal responsibility for warnings and their dissemination; (3) raising flood-risk awareness; (4) designing effective flood warning messages; (5) knowing how best and when to communicate warnings; and (6) addressing uncertainties surrounding flood warnings.
Flood warning science brings together a large body of research findings from a particularly wide range of disciplines ranging from hydrometeorological science to social psychology. In recent decades, major advances have been made in forecasting fluvial and coastal floods. Accurately forecasting pluvial events that cause surface-water floods is at the research frontier, with significant progress being made. Over the same time period, impressive advances in a variety of rapid, personalized communication means has transformed the process of flood warning dissemination. Much is now known about the factors that constrain and aid appropriate flood warning responses both at the individual and at organized, flood emergency response levels, and a range of innovations are being applied to improve response effectiveness. Although the uniqueness of each flood and the inherent unpredictability involved in flood events means that sometimes flood warnings may not perform as expected, flood warning science is helping to minimize these occurrences.
Scholars agree that the impact of a disaster in a globalized world increasingly extends beyond political and geographical boundaries, creating transboundary disaster events. Though not all disasters fit the description of a transboundary event, many embody transboundary characteristics. For instance, national and transnational financing and other resources directed toward post-disaster humanitarian relief and long-term reconstruction efforts can also create transboundary flows that cross political and geographical lines. Rebuilding after physical damage and economic losses during a disaster, the impacts of which are disproportionately higher in the poorest countries, is a costly endeavor that requires multiple sources of finance. Depending on the scale and visibility of the disaster and local capacities, financial arrangements, resources, and assistance can come from a variety of sources including the government, international institutions, and private-sector, and nongovernmental, and civil society organizations. In particular, transnational financing from bilateral donors and international financial institutions, which constitute multilateral and bilateral streams of financing for post-disaster recovery, comprise a significant percentage of recovery funding globally. Such flows, although inherently transboundary, are not well understood as a phenomenon within the transboundary disasters literature.
Three major types of agencies provide funding for post-disaster reconstruction including multilateral development banks (MDBs), also referred to as international financial institutions (IFIs); bilateral development agencies within donor countries; and United Nations (UN) development agencies. MDBs such as the World Bank are created by a group of countries that utilizes pooled contributions from national governments and additional resources, such as interest collected from loans, to finance development projects. Bilateral development agencies such as the United States Agency for International Development are institutions established by individual countries to provide development funding to nation-states; they work closely with IFIs.
Numerous questions about transnational financing for post-disaster recovery as an important component of the transboundary disaster literature remain unanswered and need further insights. What are the links among transnational stakeholders (i.e., MDBs, bilateral donors, UN agencies, and international nongovernmental organizations) and transboundary financial arrangements for post-disaster recovery? What are the aggregate impacts of transboundary financing on post-disaster reconstruction? How do transboundary financing flows occur among bilateral donors, MDBs, and local and international nongovernmental organizations? Where can scholars find data sets on post-disaster transnational financing? How does transboundary financing impact post-disaster recovery governance in recipient countries? The current state of knowledge on transboundary financing of post-disaster recovery provides some guidance on best practices and the challenges with coordinating and monitoring.
Glacier retreat is considered to be one of the most obvious manifestations of recent and ongoing climate change in the majority of glacierized alpine and high-latitude regions throughout the world. Glacier retreat itself is both directly and indirectly connected to the various interrelated geomorphological/hydrological processes and changes in hydrological regimes. Various types of slope movements and the formation and evolution of lakes are observed in recently deglaciated areas. These are most commonly glacial lakes (ice-dammed, bedrock-dammed, or moraine-dammed lakes).
“Glacial lake outburst flood” (GLOF) is a phrase used to describe a sudden release of a significant amount of water retained in a glacial lake, irrespective of the cause. GLOFs are characterized by extreme peak discharges, often several times in excess of the maximum discharges of hydrometeorologically induced floods, with an exceptional erosion/transport potential; therefore, they can turn into flow-type movements (e.g., GLOF-induced debris flows). Some of the Late Pleistocene lake outburst floods are ranked among the largest reconstructed floods, with peak discharges of up to 107 m3/s and significant continental-scale geomorphic impacts. They are also considered capable of influencing global climate by releasing extremely high amounts of cold freshwater into the ocean. Lake outburst floods associated with recent (i.e., post-Little Ice Age) glacier retreat have become a widely studied topic from the perspective of the hazards and risks they pose to human society, and the possibility that they are driven by anthropogenic climate change.
Despite apparent regional differences in triggers (causes) and subsequent mechanisms of lake outburst floods, rapid slope movement into lakes, producing displacement waves leading to dam overtopping and eventually dam failure, is documented most frequently, being directly (ice avalanche) and indirectly (slope movement in recently deglaciated areas) related to glacial activity and glacier retreat. Glacier retreat and the occurrence of GLOFs are, therefore, closely tied, because glacier retreat is connected to: (a) the formation of new, and the evolution of existing, lakes; and (b) triggers of lake outburst floods (slope movements).
Tropical cyclones, also known as hurricanes or typhoons, are one of the most violent weather phenomena on the planet, posing significant threats to those living near or along coastlines where tropical cyclone–related impacts are most pronounced. About 80 tropical cyclones form annually, a rate that has been remarkably steady over the period of reliable historical record. Roughly two thirds of these storms form in the Northern Hemisphere from about June to November, while the remaining third form in the Southern Hemisphere typically during the months of November to May. Our understanding of the global and regional spatial patterns, the year-to-year variability, and temporal trends of these storms has improved considerably since the advent of meteorological satellites in the 1960s because of advances in both remote-sensing technology and operational analysis procedures. The well-recognized spatial patterns of tropical cyclone formation and tracks were laid out in a series of seminal papers in the late 1960s and 1970s and remain an accurate sketch even to this day. Concerning the year-to-year variability of tropical cyclone frequency, the El Niño Southern Oscillation (ENSO) has by far the most dominant influence across multiple ocean basins, so much so that it is typically used as the main predictor for statistical forecasts of seasonal tropical cyclone activity. ENSO has a modulating influence on atmospheric circulation patterns, even in regions remote to the tropical Pacific, which, in turn, can act to enhance or inhibit tropical cyclone formation.
While the meteorological and climate community has come a long way in our understanding of the global and regional climatological features of tropical cyclones, as well as some aspects of the broader relationship between tropical cyclones and climate, we are still hindered by temporal inconsistencies within the historical record of storm data, particularly pertaining to tropical cyclone intensity. Despite recent efforts to homogenize the historical record using satellite-derived intensity data back to the early 1980s, the relatively short period makes it difficult to discern secular trends due to anthropogenic climate change from natural trends occurring on decadal to multidecadal time scales.
Terry Gibson and Benjamin Wisner
Non-governmental organizations (NGOs) play important roles in that they: strengthen natural hazard governance through service delivery and humanitarian response; mobilize local actors and work for advocacy, knowledge access, and integration; promote disaster risk reduction (DRR), development, and climate change adaptation (CCA) perspectives; and facilitate calls for transformative approaches. Some roles are best undertaken by large international and national NGOs (INGOs and NNGOs) and some are the province of smaller local NGOs (LNGOs). The sector as a whole plays a vital role by both challenging actors and bridge-building among them, as well as by modeling innovative practice, highlighting changing risk drivers, and engaging in policy advocacy. However, the growth of the sector has brought about challenges. The potential of NGOs is reduced by the constraints attached to much institutional funding, pressure for upward rather than downward accountability, and limited engagement by large INGOs and NNGOs with LNGOs and local people. Initiatives such as the Grand Bargain, emerging from the World Humanitarian Summit, seek to refashion and rebalance the sector. If NGOs, particularly the larger and more established organizations, prove able to address such challenges then the ability of the whole sector to support transformative change will be strengthened.
Earthquakes involve sudden shear sliding motion between large rock masses across internal contact surfaces called faults. The slip on the fault releases strain energy previously stored in the surrounding rock that accumulated due to frictional resistance to sliding. Most earthquakes are directly caused by plate tectonics, and locate in the cool, brittle rock near Earth’s surface. Events with seismic magnitude measured 8.0 or greater are called great earthquakes and involve slip of from several to tens of meters across faults with lengths from 100 to more than 1,000 kilometers. These huge ruptures tend to occur on or near plate boundaries; the largest are on shallow-dipping plate boundary faults (megathrusts) found in compressional regions called subduction zones, where one tectonic plate is thrusting under another. Some great earthquakes occur within bending or detaching plates as they deform seaward of or below a subduction zone. Yet others occur on plate boundary strike-slip faults where two plates are shearing horizontally past one another, or within deforming plate interiors. Elastic wave energy released during the fault sliding is recorded and studied by seismologists to determine the fault location, orientation and sense of sliding motion, amount of radiated elastic wave energy, and distribution of slip on the fault during the event (co-seismic slip). Geodetic methods measure elastic strain accumulation prior to an earthquake, co-seismic slip, and afterslip on the fault that occurs without earthquakes, along with viscous deformation of the mantle as it responds to the fault offset. Great earthquakes commonly locate under the ocean, and the sudden motion of the seafloor generates tsunami—gravitational water waves that can be recorded with ocean floor pressure sensors (these waves are also used to determine co-seismic slip). As seismic, geodetic. and tsunami modeling methods have progressed over the past 50 years, our understanding of great earthquake rupture processes and earthquake interactions has advanced steadily in the context of plate tectonics and improved understanding of rock friction. All faults have heterogeneous frictional properties inferred from non-uniform sliding during each event, with areas of large slip instabilities called asperities having slip-velocity weakening friction and other areas having slip-velocity strengthening friction that results in stable sliding. The seismic wave shaking and tsunami waves can cause great devastation for humanity, so efforts are made to anticipate future earthquake hazards. As plate tectonics steadily move Earth’s plates, elastic strain around plate boundary faults accumulates and releases in a repeated stick-slip sliding process that causes a limited degree of regularity of faulting. Given the history of prior earthquakes on a given fault, we can identify seismic gaps where future slip events are likely to occur. With geodesy we can also now measure locations of accumulating slip deficit relative to plate motions, as well as variation in seismic coupling, which characterizes the fraction of plate motion accounted for by earthquake failure.
Russ S. Schumacher
Heavy precipitation, which in many contexts is welcomed because it provides the water necessary for agriculture and human use, in other situations is responsible for deadly and destructive flash flooding. Over the 30-year period from 1986 to 2015, floods were responsible for more fatalities in the United States than any other convective weather hazard (
A range of environmental and social dimensions of disasters occur in or are affected by the mountain cryosphere (MC). Core areas have glaciers and permafrost, intensive freeze-thaw, and seasonally abundant melt waters. A variety of cryospheric hazards is involved, their dangers magnified by steep, high, and rugged terrain. Some unique threats are snow or ice avalanches and glacial lake outburst floods. These highlight the classic alpine zones, but cryospheric hazards occur in more extensive parts of mountain ecosystems, affecting greater populations and more varied settings. Recently, habitat threats have become identified with global climate warming: receding glaciers, declining snowfall, and degrading permafrost. Particularly dangerous prospects arise with changing hazards in the populous mid-latitude and tropical high mountains. Six modern calamities briefly introduce the kinds of dangers and human contexts engaged. Disaster style and scope differs between events confined to the MC, others in which it is only a part or is a source of dangerous processes that descend into surrounding lowlands. The MC is also affected by non-cryospheric hazards, notably earthquake and volcanism. In human terms, the MC shares many disaster risk issues with other regions. Economy and land use, poverty or gender, for instance, are critical aspects of exposure and protections, or lack of them. This situates disaster risk within human ecological and adaptive relations to the predicaments of cold and steepland terrain. A great diversity of habitats and cultures is recognized. “Verticality” offers a unifying theme; characterizing the MC through ways in which life forms, ecosystems, and human settlement adjust to altitudinal zones, to upslope transitions, and the downslope cascades of moisture and geomorphic processes. These also give special importance to multi-hazard chains and long-runout processes including floods. Traditional mountain cultures exploit proximity and seasonality of different resources in the vertical, and avoidance of steepland dangers. This underscores sustainability and changing risk for the many surviving agro-pastoral and village economies and the special predicaments of indigenous cultures. Certain common stereotypes, such as remoteness or fragility of mountain habitats, require caution. They tend to overemphasize environmental determinism and underestimate social factors. Nor should they lead to neglect of wealthier, modernized areas, which also benefit most from geophysical research, dedicated agencies, and expert systems. However, modern developments now affect nearly all MC regions, bringing expanding dangers as well as benefits. Threats related to road networks are discussed, from mining and other large-scale resource extraction. Disaster losses and responses are also being rapidly transformed by urbanization. More broadly, highland–lowland relations can uniquely affect disaster risk, as do transboundary issues and initiatives in the mountains stemming from metropolitan centers. Anthropogenic climate warming generates dangers for mountain peoples but originates mainly from lowland activities. The extent of armed conflict affecting the MC is exceptional. Conflicts affect all aspects of human security. In the mountains as most other places, disaster risk reduction (DRR) policies have tended to favor emergency response. A human ecological approach emphasizes the need to pursue avoidance strategies, precautionary and capacity-building measures. Fundamental humanitarian concerns are essential in such an approach, and point to the importance of good governance and ethics.
Like any other species, Homo sapiens can potentially go extinct. This risk is an existential risk: a threat to the entire future of the species (and possible descendants). While anthropogenic risks may contribute the most to total extinction risk natural hazard events can plausibly cause extinction.
Historically, end-of-the-world scenarios have been popular topics in most cultures. In the early modern period scientific discoveries of changes in the sky, meteors, past catastrophes, evolution and thermodynamics led to the understanding that Homo sapiens was a species among others and vulnerable to extinction. In the 20th century, anthropogenic risks from nuclear war and environmental degradation made extinction risks more salient and an issue of possible policy. Near the end of the century an interdisciplinary field of existential risk studies emerged.
Human extinction requires a global hazard that either destroys the ecological niche of the species or harms enough individuals to reduce the population below a minimum viable size. Long-run fertility trends are highly uncertain and could potentially lead to overpopulation or demographic collapse, both contributors to extinction risk.
Astronomical extinction risks include damage to the biosphere due to radiation from supernovas or gamma ray bursts, major asteroid or comet impacts, or hypothesized physical phenomena such as stable strange matter or vacuum decay. The most likely extinction pathway would be a disturbance reducing agricultural productivity due to ozone loss, low temperatures, or lack of sunlight over a long period. The return time of extinction-level impacts is reasonably well characterized and on the order of millions of years. Geophysical risks include supervolcanism and climate change that affects global food security. Multiyear periods of low or high temperature can impair agriculture enough to stress or threaten the species. Sufficiently radical environmental changes that lead to direct extinction are unlikely. Pandemics can cause species extinction, although historical human pandemics have merely killed a fraction of the species.
Extinction risks are amplified by systemic effects, where multiple risk factors and events conspire to increase vulnerability and eventual damage. Human activity plays an important role in aggravating and mitigating these effects.
Estimates from natural extinction rates in other species suggest an overall risk to the species from natural events smaller than 0.15% per century, likely orders of magnitude smaller. However, due to the current situation with an unusually numerous and widely dispersed population the actual probability is hard to estimate. The natural extinction risk is also likely dwarfed by the extinction risk from human activities.
Many extinction hazards are at present impossible to prevent or even predict, requiring resilience strategies. Many risks have common pathways that are promising targets for mitigation. Endurance mechanisms against extinction may require creating refuges that can survive the disaster and rebuild. Because of the global public goods and transgenerational nature of extinction risks plus cognitive biases there is a large undersupply of mitigation effort despite strong arguments that it is morally imperative.
Brett F. Sanders
Communities facing urban flood risk have access to powerful flood simulation software for use in disaster-risk-reduction (DRR) initiatives. However, recent research has shown that flood risk continues to escalate globally, despite an increase in the primary outcome of flood simulation: increased knowledge. Thus, a key issue with the utilization of urban flood models is not necessarily development of new knowledge about flooding, but rather the achievement of more socially robust and context-sensitive knowledge production capable of converting knowledge into action. There are early indications that this can be accomplished when an urban flood model is used as a tool to bring together local lay and scientific expertise around local priorities and perceptions, and to advance improved, target-oriented methods of flood risk communication.
The success of urban flood models as a facilitating agent for knowledge coproduction will depend on whether they are trusted by both the scientific and local expert, and to this end, whether the model constitutes an accurate approximation of flood dynamics is a key issue. This is not a sufficient condition for knowledge coproduction, but it is a necessary one. For example, trust can easily be eroded at the local level by disagreements among scientists about what constitutes an accurate approximation.
Motivated by the need for confidence in urban flood models, and the wide variety of models available to users, this article reviews progress in urban flood model development over three eras: (1) the era of theory, when the foundation of urban flood models was established using fluid mechanics principles and considerable attention focused on development of computational methods for solving the one- and two-dimensional equations governing flood flows; (2) the era of data, which took form in the 2000s, and has motivated a reexamination of urban flood model design in response to the transformation from a data-poor to a data-rich modeling environment; and (3) the era of disaster risk reduction, whereby modeling tools are put in the hands of communities facing flood risk and are used to codevelop flood risk knowledge and transform knowledge to action. The article aims to inform decision makers and policy makers regarding the match between model selection and decision points, to orient the engineering community to the varied decision-making and policy needs that arise in the context of DRR activities, to highlight the opportunities and pitfalls associated with alternative urban flood modeling techniques, and to frame areas for future research.