Natural Hazards Identification and Hazard Management Systems (2024)

Table 1. Selected Natural Hazard Impacts in the United States

Source: Modified from USGS (2007).

Earthquakes

The development of robust and timely earthquake predictions has proved to be elusive, as understanding earthquake mechanisms is challenging and a very active area of research. Understanding earthquake processes requires data and observations at the depth where earthquakes are generated. Recently, in 2007, a deep borehole was drilled on the San Andreas Fault at Parkfield, California, and heavily instrumented to collect a wide array of information during a long-awaited earthquake. Similar studies, although expensive and long term, are needed.

Landslides

Landslide processes are complex, chaotic, and not fully understood, as most mass movement involves solids moving as a liquid does. Addressing landslide risks requires a predictive understanding of triggering mechanisms and thresholds for triggering. Once improved and more realistic models of landslide processes are developed, they will need to be applied to real-time warning systems. A key input to building these improved models requires modern geologic maps at a high degree of resolution. Unfortunately, geologic maps at the necessary resolution are not available in most parts of the world, including large areas of the United States.

Tsunamis

Tsunamis are almost exclusively generated by specific types of earthquakes, although landslides are responsible for about 15% of tsunamis worldwide (Geological Society of London, 2014). Tsunamis are generated mainly by earthquakes that tend to be greater than magnitude 7.0 and that occur under water on major thrust faults along the edge of subducting tectonic plates. Because of global seismic monitoring and the speed at which data can be analyzed relative to the accurate epicenter location, magnitude, and type of faulting, geoscientists can determine if an event has the potential to generate a tsunami. This information, coupled with the ability to monitor wave height in real time and robust modeling of the speed and direction of the tsunami waves, have allowed for significant early warning of an approaching tsunami. Although more research is needed to improve the performance of models, there currently are functional tsunami warning systems in most of the at-risk parts of the world. The f*ckushima earthquake that struck in Japan in November 2016 resulted in the issuance of an effective tsunami warning that demonstrates the robustness of the warning network.

Assessing the long-term frequency of tsunami threats requires detailed geologic mapping of tsunami deposits. This mapping will provide information to support more accurate hazard assessments of the areal extent, thickness of tsunami deposits, and frequency of occurrence of tsunamis. In recent years, the identification of tsunami deposits in the Caribbean has led to a better understanding of tsunami risks, and in turn to the installation of more seismic monitoring stations and sea-surface-level monitoring buoys, resulting in a real-time tsunami warning system.

Coastal Storms

In 1900, a powerful hurricane (known as the Great Storm of 1900) swept across the Gulf of Mexico, making landfall on Galveston Island in Texas in the United States. Because modern monitoring was not available at the time, this hurricane was essentially unpredicted by the weather service, and no significant warnings were issued. The storm resulted in the deaths of about 8,000 of the 37,000 residents of Galveston. It still ranks as the worst natural disaster in US history because of the large loss of life—indeed, there was more loss of life in this storm than in all 325 of the major coastal storms that struck the United States from then until 2011 (Hudson, 2011). Since 1900, numerous other major storms (predominantly hurricanes, typhoons, and cyclones) have caused major loss of life and economic losses throughout the world. Some notable examples include Hurricane Katrina in 2005 and Superstorm Sandy in 2012 in the United States, and Typhoon Haiyan in 2013 and Cyclone Tracy in 1974 in Asia. What is remarkable about these storms is the impact that these coastal storms had on heavily populated urban areas. Cyclone Tracy caused unprecedented damage to Darwin, Australia, and Typhoon Haiyan, characterized as a superstorm because of its vast size, caused enormous damage to the Philippines and China. Hurricane Katrina resulted in the near-complete flooding of New Orleans, Louisiana, following the failure of levees that proved to be inadequate for this scale of storm. Economic losses in the United States during 2005, largely due to Katrina, totaled in the hundreds of billions of dollars, making it the most expensive hurricane season in US history. Superstorm Sandy made landfall in New Jersey and went on to cause major damage to New York City and Long Island as well. The storm surge resulted in widespread flooding, including parts of the metropolitan New York commuter transit rail systems. Recovery and rebuilding after the event were well underway in 2016, but much remains to be done to ensure that future storms will not be as catastrophic. These storms all affected urban settings, demonstrating that society must recognize the risk of natural hazards on significant infrastructure in areas with high population densities that may not be able to withstand the impacts of such events.

In addition, research is needed to better predict the severity of storms and more accurately determine their tracks. Much has been accomplished to date, but more accuracy is needed to effectively mitigate impacts of the storm. Better prediction of rainfall, storm surge, wind velocity, and coastal erosion is needed.

Earthquakes

Historical information on previous hazardous events like earthquakes is critical to assessing what events can be expected in the future. For example, does a particular fault have a history of producing large-magnitude earthquakes, and at what frequency do these large events occur? One example is the North Anatolian fault in Turkey, which has generated large earthquakes in a fairly consistent manner for thousands of years (USGS, 2000). The magnitudes of these events typically are about the same, but the location of the ruptured fault segment moves generally east to west on each subsequent event. The last earthquake along this fault occurred in Izmit, Turkey, in 1999, and because Istanbul lies to the west along the same fault, the hazard from an earthquake in the Istanbul region was elevated. Fortunately, a global seismic hazard map (Fig. 2) was produced by a consortium of international geoscience organizations to define the level of hazard and ground shaking in large regions of the globe (Giardini, Grunthal, Shedlock, & Zhang, 2003).

Although this global view is important, more resolution is required for policymakers to mitigate the seismic hazard through the creation of building codes designed to reduce damage. Policymakers also need to implement programs to educate the public on appropriate responses during such events to reduce injury and death. Figure 3 presents a map of the conterminous United States that illustrates the seismic hazard and peak ground acceleration that can be expected with a 2% probability of exceedance in 50 years (Petersen et al., 2015). It is noteworthy that the seismic risk has been elevated in the north-central Oklahoma and southern Kansas area due to recent increase in seismicity induced by the injection of fluids into the subsurface related to human activities.

Tsunamis

Tsunamis are almost exclusively generated by earthquakes, and because of effective global seismic monitoring, it is possible to determine, in a matter of minutes, if a specific earthquake potentially can generate a tsunami. Robust models exist that can predict the arrival of a tsunami even an ocean away from where it was generated. Of course, from a public safety perspective, evacuation of people requires time, and often the areas near the earthquake lack adequate response time; this was the case in both the Sumatra-Andaman and Tohoku earthquakes of 2004 and 2011, respectively. Both these events caused major economic losses and loss of life because of the size and location of the event relative to people and infrastructure.

Volcanoes

In the case of volcanic eruptions, geoscientists have a distinct advantage because the locations of the world’s volcanoes are generally known. However, the hazards can have a high impact, including lava flows, volcanic gases, pyroclastic flows, ash falls, and lahars (wet debris flows that clog rivers and have the potential to cause major flooding events). Figure 4 shows a world map of volcanoes, earthquakes, impact craters, and plate tectonics (Simkins, Tilling, Vogt, Kirby, Kimberly, & Stewart, 2006). However, to fully understand the risk from a specific volcano requires both monitoring it and taking its detailed eruptive history to determine the frequency, type, and severity of eruptions. Documenting such an eruptive history requires detailed geological mapping, which involves extensive field efforts. The information regarding a volcano’s potential severity or magnitude is described by the Volcanic Explosivity Index (VEI). The VEI was proposed in 1982 and is based on several criteria, including duration of eruption and height of eruption column (Newhall & Self, 1982). The VEI is shown graphically in Figure 5 (American Geosciences Institute, 2016).

Geomagnetic Storms

Geomagnetic storms are another, if less obvious, natural hazard. The Earth’s magnetic field is defined by two processes. The secular field results from the unequal rotation of the core and mantle of the Earth, called the dynamo. Short-term changes in the magnetic field are caused by solar or geomagnetic storms triggered by coronal mass eruptions that pummel the Earth with highly charged ions that rain down on it in 11-year activity cycles. On March 13, 1989, a geomagnetic storm resulting from a solar outburst struck the Earth, triggering instabilities in the electric power grid that serves much of eastern Canada and the United States. The storm led to blackouts for more than 6 million customers and caused tens of millions of dollars in damage and economic losses. In addition, geomagnetic storms may disrupt telecommunications (with the advent of smartphone technology, personal communication has been put at risk as well), damage satellites, endanger the safety of humans in space, cause navigation problems because of the disruption of global positioning satellite (GPS) systems, and damage long north-south trending electrical lines and pipelines that transport fuel and water (because corrosion rates are accelerated). Insurance losses are expected to increase with society’s increasing reliance on electronics. Research is needed to improve the predictability of future geomagnetic storms so that their impacts can be reduced or avoided. Several articles that have been published in Earth magazine provide a good overview on geomagnetic storms (Morton, 2014; Thompson, 2013; Viereck, 2015).

Landslides

Landslides have not been extensively mapped globally, and only a handful of landslide-prone areas are actually monitored. Almost all nations face significant landslide and ground failure hazards. Landslides occur due to slope instability and can occur either very rapidly or so slowly as to be imperceptible in real time. They can be triggered by rainstorms, earthquakes, wildfires, volcanic eruptions, and human activity. Landslide inventories are the basis for susceptibility mapping, and ultimately hazard and risk assessment mapping as well. Generally, because of the lack of understanding of landslide processes, probabilistic modeling is used to create landslide hazard maps. Landslide inventories are determined by identifying and locating old landslide features and understanding the complex interactions among slope, soil, rock type, vegetation, and groundwater-table height. Detailed geologic, soil, and hydrogeologic maps at appropriate scales are needed, along with detailed field reconnaissance.

Although it is very difficult to get accurate estimates because of the obvious mass failures and less obvious creep, both of which cause substantial infrastructure damage. In the United States, an estimated 25 to 50 deaths annually are a result of landslides and ground failure. In addition, annualized economic losses in the United States are estimated at $2 billion to $3.5 billion (USGS, 2007). In general, the economic loss tally is based on large landslides; the costs of restoration related to smaller events that may close a stretch of highway (and are generally repaired quickly by local government or homeowners) are not included in the estimates of economic losses, so the true costs may be significantly larger. Globally, numerous large catastrophic landslides have occurred since 1900 (AGI, 2016), and these are noted on Table 2.

The U.S. Geological Survey (USGS) last published a landslide hazard map for the conterminous United States in 1982 (USGS, 1997). With the advent of new technology, such as light detection and ranging (LIDAR), very accurate and precise measurements of topography can be taken. This technology is being used in specific areas for landslide mapping and for other natural hazard work like fault mapping, volcano studies, and coastal mapping. Expanded global use of this technology and other advanced remote sensing techniques that will be developed in the coming years are critical to meeting the basic need for assessing natural hazard risks globally.

Much progress has been made toward understanding the triggering of precipitation-induced landslides; however, rainfall monitoring at the detailed spatial resolution required is still quite rare. For example, in the United States, the USGS and the National Weather Service partnered to develop a demonstration early warning flash-flood and debris-flow system in 2005 (USGS, 2005a). The project focused on southern California, where there is adequate real-time data on rainfall. These data were derived from a network of advanced radar sites and from a dense network of real-time rain gauges. In addition, significant research has been conducted in this area on the rainfall thresholds required to initiate debris flows. The demonstration worked as planned, and it could be replicated across the globe with adequate investment in infrastructure, monitoring, and research.

Tsunamis

On November 21, 2016, a magnitude 6.9 earthquake was reported by the Japan Meteorological Office and the USGS off the coast of f*ckushima Prefecture in Japan. This earthquake produced a small tsunami in the area but did not cause significant damage. This is in stark contrast to the March 11, 2011, magnitude-9 event in approximately the same area, which claimed 18,000 lives and caused significant damage to infrastructure, including the f*ckushima Daiichi nuclear power generating facility, which caused significant widespread environmental contamination. These examples highlight the challenge of large earthquakes causing tsunamis near populated areas with sensitive infrastructure. Without the advantage of distance, there is a limited warning time during which tsunami hazard zones can be evacuated. These factors must be incorporated into hazard and risk assessments and any proposed actions to mitigate the hazard.

Earthquakes

Some nations have invested heavily in the development of extensive seismic monitoring networks, including Japan and Taiwan, which have among the world’s densest arrays of seismic stations. Figure 6 shows a map of Japan and a map of California that identify the location of seismic sensors as part of the Advanced National Seismic System in the United States and the national government in Japan. The high density of seismic sensors in Japan is needed to ensure adequate early warning of earthquakes (http://earthquake.usgs.gov/research/earlywarning/nextsteps.php). Where the probability of seismic events in areas with dense population and infrastructure is high, the investment in such seismic systems is economically defensible. On the other hand, global monitoring can help as well. The United States maintains a global seismographic network of approximately 100 state-of-the-art seismometers that are capable of monitoring moderate- to large-magnitude events anywhere on Earth. The stations are strategically located around the world. Interestingly, there is a station at the South Pole in Antarctica that has what is generally considered the quietest seismometer on Earth because of its remote location and the lack of background noise associated with human activities. A map showing the location of seismic stations and all earthquakes larger than 6.0 for the period from 2000–2010 is presented in Figure 7 (Gee & Leith, 2011).

In the case of seismic monitoring, having near-real-time information and advanced instrumentation vastly improves the quality of information for researchers, national security agencies, emergency management workers, and the general public. Initially, seismometers were analog devices designed to be accurate for a certain range of frequencies of vibration and amplitude of motion. These band-limited instruments were technology limiting for the seismologist, generally requiring networks of weak motion seismometers to monitor small, local earthquakes and large, distant earthquakes. In addition, networks were established to monitor the strong motion required to understand the intense ground shaking that affects structures. It is also noteworthy that since this instrumentation was analog, most analysis required intense human involvement, which took significant time and did not allow the quick real-time response that society needed to reduce the risk to life and property substantially.

With the advent of digital technology, modern instrumentation has replaced the analog instruments of the past. These seismic monitors have both broad frequency-band capability and large dynamic ranges to measure ground shaking accurately. In addition, because the monitors produce digital records, information can be analyzed in near-real time and automatically through the use of high-speed computing. This advancement has created an entirely new audience for earthquake information—namely, emergency responders and the general public.

In 1998, there were approximately 1,700 weak-motion seismic instruments and 1,400 strong-motion seismometers in the United States (NRC, 2006). This network is in need of improvement, and the USGS has advocated a significant increase in the seismic monitoring network for the United States (USGS, 1999). It proposed a significant expansion and modernization of the seismic network (i.e., adding several thousand instruments) for a capital cost of approximately $170 million and an annual operating cost of $47 million in 1999 dollars. One aspect of the proposal was to enhance seismic monitoring in urban areas. The number of stations in each urban area is determined by the earthquake hazard and the size of the population at risk.

Los Angeles and San Francisco were the highest-priority urban areas, each requiring about 1,000 instruments. It is interesting to note that at the same time, significant government investment was being made in the United States to support a major research effort to understand the deep geologic structure of the land. This research effort, entitled EarthScope, used seismic monitors to accomplish their research goals. Portable regional arrays of seismometers were moved across the country to better understand the geologic structure of various regions. As these studies were completed, some of the instrumentation has been left in place to support the proposed expansion and modernization of the seismic network of the United States. This is a good example of the efficient and effective dual use of expensive instrumentation.

Generally, robust seismic monitoring is designed using a tiered approach including a global component, national component, regional component, and local component. In some instances, buildings themselves are instrumented to determine the response of the structure to intense ground shaking. This information is particularly valuable to structural engineers and building code officials. Also, pilot efforts are under way to use seismic monitoring as a rapid response tool. For earthquakes that are located moderate distances from infrastructure, it is possible to issue a warning after the earthquake occurs, but before the arrival of potentially damaging seismic waves. Although it does not constitute a prediction, it does allow certain actions to be taken that can lessen the impact of the shaking. For example, trains could be stopped so that they don’t derail, electrical grids could be shut down so that they could be brought up more quickly (and with less damage) following the shaking, surgeons in hospitals could be given a moment of advance warning so that they could react accordingly during their procedures, and bridges could be closed so that traffic was not on them during the shaking.

On December 26, 2004, a magnitude-9.0 earthquake off the coast of Sumatra, Indonesia, generated a major tsunami that resulted in the loss of 200,000 lives in 11 countries. The lack of tsunami hazard assessment, as well as inadequate monitoring and lack of public awareness, contributed to the scale of the loss. Following the event, significant effort was spent increasing seismic and other monitoring to mitigate the tsunami hazard in the Indian Ocean. A key lesson learned from that process is the critical need for free and timely sharing of seismic data following major events like the Sumatra earthquake that have a significant, if not global, impact. Unfortunately, the free sharing of information is often not permitted in many nations because of concerns about national security. Multilateral and diplomatic efforts are needed to improve the rapid exchange of data.

Volcanoes

Globally, Japan, Indonesia, and the United States have the largest number of active volcanoes within their borders. These nations have very good monitoring programs, but the systems require consistent upgrades as new advances in monitoring are made. Many volcanoes are monitored through the use of satellite imagery, particularly in remote areas. This technology has been used effectively in several instances. The successful evacuation at Mount Pinatubo in the Philippines in 1991 can be attributed directly to the availability of advanced remote sensing data that provided geoscientists the necessary information to determine that an eruption was imminent.

Although it is less sophisticated, remotely sensed information is critical to monitoring active volcanoes worldwide. For example, there are 41 active volcanoes on the islands that make up the Aleutian chain. Many of these islands are very remote, and some do not have access to either power or telecommunications. However, the risk to air safety and native peoples is significant. There has been a major effort during the past 25 years to install seismic monitoring equipment on many of these islands so that early warning of volcanic unrest can be observed. Also, monitoring is increased during periods of volcanic unrest. More sophisticated remote sensing is deployed if possible, along with the deployment of additional seismic stations whose records can be analyzed to determine the movement of magma in the subsurface. In addition, advanced monitoring of volcanic gases is employed to determine if an eruption is imminent. Precise measurements of changes in elevation are also made on the volcano to detect any deformation of the land surface that is a result of its volcanic activity.

There are also a number of volcanic observatories located around the world. These are located at high-risk volcanoes or at volcanoes that are ideally suited as field laboratories for detailed research studies into volcanic processes. The first of these observatories was founded in the early 1900s at Kilauea volcano on the Big Island of Hawaii. The observatory was founded specifically in response to the catastrophic eruption of Mount Pelee on Martinique in the Caribbean in 1902, which resulted in an almost complete loss of human life (only one survivor was reported) in the island’s capital, St. Pierre.

Flooding and Drought

The United States has an effective network of real-time streamflow monitoring gauges and groundwater observation wells. This national network is critical for determining the severity of flooding that an area may experience under various flow conditions. It is also useful for determining drought conditions. The streamflow and observation well information is freely available to the public through the Internet and is used by a variety of audiences ranging from recreationalists to determine optimum conditions for fishing and boating to emergency managers for flood and drought response. Real-time monitoring of floods is critical to determining the extent of potential flood damage and to avoiding economic losses and loss of human life. Figure 8 shows a series of maps of the United States for November 30, 2016, depicting current streamflow characteristics, flood conditions, previous-day streamflow, and current drought conditions. Other nations have similar networks, but regrettably many parts of the world lack this information.

Now coupled with the extensive NEXRAD network, which tracks precipitation rates of active storms, the data from stream gauges are used in flood prediction and stream response models, which leads to accurate and rapid warnings. In addition, the integration of these data has led to advanced modeling techniques so that the streamflow and stage can be estimated for ungauged stream reaches.

Satellite and other remotely sensed data are now being used routinely to monitor hazards. Landsat satellites can be used to compute a greenness index, which can be used as an early warning system for drought. This has been effectively used, specifically in Africa to ensure that relief supplies are strategically located to mitigate the human toll associated with famine. Similarly, the GRACE satellite can determine the volume of groundwater in storage and be used to estimate areas of land subsidence and diminished groundwater availability. Given multiple passes by the satellite, data can be analyzed to determine how the system is changing. These examples show the potential for remotely sensed data in hazard monitoring.

Coastal Storms

The impact of coastal storms is another hazard that can cause severe long-term consequences, in addition to human and property losses. With the advent of advanced remote-sensing information using LIDAR, it is possible to determine the affected areas very accurately for various storm surge scenarios. In some cases, communities have relocated at significant expense to higher and safer ground. Following concerns about increased coastal erosion during storms, two communities in the United States that have recently decided to relocate farther inland to avoid inundation, the loss of infrastructure, and ensure public safety are Isle de Jean Charles, Louisiana, and Shishmaref, Alaska.

Social Media and the Internet

With the advent of social media, more information is being supplied by citizen scientists through a process called crowdsourcing. Several examples of crowdsourcing exist within the earthquake community. Some use apps on smartphones that allow volunteers to report the intensity of the shaking in the area where the phone is located. Other apps use a smartphone’s internal sensor to detect shaking and send data to a central database. Earlier efforts focused on reporting over the Internet (Deatrick, 2016).

The advent of citizen scientists plays a critical role in increasing general public awareness of natural hazards and other phenomena. However, the observations made by various citizen scientists also provide timely and important data to geoscientists. For example, one program called “Did You Feel It?” encourages people worldwide to go online and report their observations during an earthquake. This information is used to construct near-real-time maps of shaking intensity and damage caused. This is extremely valuable to emergency responders and researchers alike. Also, individuals who participate in the program feel satisfied that they have somehow contributed positively to a difficult situation. Similarly, citizen scientists are also contributing to earthquake research and have installed inexpensive seismographs in their homes or offices.

The landslide community in the United States also has implemented a program that allows citizen scientists to report their landslide observations. The goal is to have a much more comprehensive database upon which to base a national landslide hazard assessment (USGS, 2012). Finally, there are numerous citizen scientist programs globally addressing water availability and water quality observations. One such program is the World Water Monitoring Challenge, which engages people to conduct basic monitoring of their local bodies of water.

The use of social media and the Internet has a great deal of potential to assist in natural hazard monitoring, and advances across all hazards can be expected for many years to come.

Volcanoes

To emphasize the importance of public safety, it is important to note that an estimated 500 million people live close enough to active volcanoes to be negatively affected during eruptions (Geological Society of London, 2014). One example that highlights the importance of monitoring information to assist the public dealing with hazardous events is the disruption of civil air travel in 2010 as a result of the eruption of Eyjafjallajökull in Iceland, which caused havoc to the traveling public across northern and western Europe. The air travel disruption caused economic losses, as well as much personal inconvenience. Another example is the near-crash of KLM Flight 867 on December 14, 1989. On a final approach to Anchorage Airport following an uneventful flight over the North Pole from Amsterdam, a 747 jumbo jet with 245 passengers lost power in all engines after flying through a volcanic ash plume from the eruption of Mount Redoubt. Fortunately, the pilots were able to restart the engines during the descent and land safely in Anchorage with no loss of life, but $80 million worth of damage was done to the aircraft.

This was not the first time that commercial aircraft have encountered volcanic ash plumes. For example, in 1982, a British Airways jumbo jet had lost its engines while flying into an ash cloud from Galunggung in Indonesia. After the Anchorage event, however, it became clear that the traveling public were facing a major volcanic ash hazard. In response, the World Meteorological Organization and the International Civil Aviation Organization developed training programs and a series of global centers, called Volcano Ash Advisory Centers (VAACs), in the mid-1990s to track volcanic ash so that information on dangerous plumes could be provided to civil aviation in an effort to avoid the ash hazard (Guffanti & Miller, 2002). During the 2010 Icelandic eruption, such procedures and information were used to avoid volcanic ash for commercial air traffic.

Earthquakes

The users of hazard information include government leaders, emergency managers, relief managers, the media, decision makers (who determine where public funds should be committed), insurance underwriters, social scientists such as psychologists and social workers, the medical community, the business community, and the general public. Some audiences have response responsibilities immediately following a disaster, while others play a strong role in anticipating a hazardous event and implementing appropriate mitigations either for direct impact of the event through strengthened infrastructure and preparedness or for reducing the loss of life and property following the event. Generally, groups that respond to an event want timely and accurate information so that their response is focused and goes smoothly, resulting in the saving of lives. PAGER is an example of the rapid delivery of damage assessment information globally following any major earthquake. Developed by the USGS, PAGER distributes alarms on numerous social media outlets (USGS, 2005b). The system provides near-real-time information on the location, magnitude, and depth of an earthquake, as well as an estimate of the number of people exposed to varying levels of shaking, a description of the response of the region’s infrastructure to shaking, and a measure of confidence in the information. This information is extremely useful in terms of an efficient and effective emergency response to an event.

Groups that have a strong role prior to an event want information that can be used to identify risk. Risk reflects the potential impact on a community or region. A generalized risk diagram with the risk for various natural hazards identified is shown in Figure 9. As can be seen, natural hazards cover a wide range of frequencies of occurrence and severity of impact. For example, there are numerous earthquakes annually that have magnitudes less than 6, which generally cause little damage or significant human death. However, there are many fewer earthquakes with magnitudes greater than 6, which may cause great damage and significant loss of life.

Risk is defined as “the probability of harmful consequences or expected losses resulting from interactions between natural hazards or human-induced hazards and vulnerable conditions” happening in a given time frame (Executive Office of the President, 2005, p. 17). For example, if there is a high likelihood of a large earthquake in a region, what is the size of the population that will be affected? Is the infrastructure of the region built to withstand potential shaking? Risk can be computed for all hazards, but the accuracy of that assessment requires understanding the likelihood of an event of a given severity and the expected impact on life and property.

Flooding

Floodplain mapping is a good example of minimizing both loss of life and economic loss due to flooding. In the United States, the annualized economic losses due to flooding exceed all other natural hazards. In the 1990s, flood losses totaled $50 billion in the United States (NWS-HIC, 2001). In 2012–2013, insurance losses in the United Kingdom due to flooding were approximately £1 billion ($1.4 billion; Geological Society of London, 2014). A key product that should be used to determine risk-associated flooding is the floodplain map, which delineates the potential extent of flood-associated events that have a low probability of occurrence (often the so-called 100-year or 500-year flood is used as a benchmark).

Policymakers may decide to mitigate risk by reducing building in floodplain areas. But certainly, insurance providers base their premiums on the location of structures relative to the floodplain. Similarly, more stringent building codes may be enacted in earthquake-prone areas to reduce building collapse, thereby saving lives and the cost of repair and rebuilding and ensuring that critical infrastructure such as hospitals and schools are located in the most risk-minimized locations.