Fujiwhara effect, Typhoons Ione and Kirsten, August 24, 1974. Image ID: wea00481, NOAA’s National Weather Service (NWS) Collection.
Storm Progression
| Storm Type | Top Wind Speeds | Duration | Metrological Features |
|---|---|---|---|
| Tropical/Easterly Wave | variable | 24 hours | Low pressure moving westward through the trade wind easterlies. Associated with extensive cloudiness and showers. |
| Tropical Disturbance | variable | >24 hours | Area of organized convection. Often the first developmental stage of any subsequent tropical depression, storm, or cyclone. |
| Tropical Depression | <16 m/s (38 mph) | Having 1 or more closed isobars (line drawn on the weather map of equal barometric pressures). | |
| Tropical Storm | >17 m/s (39 mph) | No classical developed eye. | |
| Rain bands form outward from the center | |||
| Given a name and it is tracked. | |||
| Cyclone | >33 m/s (74 mph) | Classic well-developed eye and eyewall. Clear spiral shape with formation of spiral rain bands emanating from eye wall. |
Tropical cyclones cause loss of life and property damage primarily due to storm surge, strong winds, and floods from the inundating rains. Storm surge is the rising ocean water level driven by wind and the speed of the storm against the coastline along shallow ocean shelves. This results in significant coastal flooding. It is expressed in terms of height above normal tide levels. In 2012, Hurricane Sandy created a catastrophic storm surge due to its tremendous size, causing an estimated 147 direct deaths in the states of New York and New Jersey.6 In addition, secondary disasters often accompany these cyclones by creating or exacerbating new or existing hazards. Such secondary events induced by a hurricane include tornadoes, landslides, mudslides, and flooding due to levee breaches.
Tropical cyclones are graded based on wind speed using the Saffir-Simpson scale (Table 36.3) or the Australian Tropical Cyclone Intensity scale. Both scales use a 1–5 rating, based on the tropical cyclone’s present intensity and peak sustained wind speed. These scales are used to estimate potential property damage and the degree of flooding expected along the coast after the tropical cyclone has made landfall. It is important to remember that although the intensity of the winds is predictive of damage, the speed with which a storm travels through an area also has significant impact. A slow-moving storm can cause more damage by increasing the geographic area exposure time to high winds, rainfall, and flooding.
Saffir-Simpson Hurricane Scale
| Category | km/h (mph) | Storm Surge meters (feet) | Damage caused |
|---|---|---|---|
| Tropical Depression | 0–62 (0–38) | 0 (0) | None |
| Tropical Storm | 63–117 (39–73) | 0–0.9 (0–3) | None |
| 1 Minimal | 119–153 (74–95) | 1.2–1.5 (4–5) | Minimal to buildings and structures; primarily to unanchored mobile homes, shrubbery, and trees; some coastal road flooding and minor pier damage |
| 2 Moderate | 154–177 (96–110) | 1.8–2.4 (6-8) | Some roofing material, door, and window damage; considerable damage to vegetation, mobile homes, and piers; small craft in unprotected anchorages break moorings |
| 3 Extensive | 178–209 (111–130) | 2.7–3.7 (9–12) | Structural damage to small residences and utility buildings with a minor amount of curtain wall failures; mobile homes are destroyed; flooding near the coast destroys smaller structures with larger structures damaged by floating debris |
| 4 Extreme | 210–249 (131–155) | 4–5.5 (13–18) | More extensive curtain wall failures with some complete roof structure failure on small residences; major beach erosions; major damage to lower floors of structures near the shore |
| 5 Catastrophic | >250 (>156) | >5.5 (>18) | Complete roof failure on many residences and industrial buildings; some complete building failures with small utility buildings blown over or away; major damage to lower floors of all structures located less than 3 m (15 ft.) above sea level |
One of the most devastating meteorological manifestations of the tropical cyclone is its storm surge. The height of the surge can be calculated, and in the United States, the SLOSH (Sea, Lake, and Overland Surges from Hurricanes) computer program is frequently used for this purpose. Depending on the slope of the continental shelf, the storm surge can be quite massive and destructive. Its impact is exacerbated by topographical changes in the local landscape due to deforestation, topsoil erosion, and increased coastal construction. With deforestation and reclaiming of marshlands along coastlines, no natural barriers exist to block the water and wind. Therefore, the cyclone’s effects are carried much further inland, increasing the area and population vulnerable to such devastation as landslides and building collapse (Figure 36.2).
Cyclone Evan left devastation over Fiji in 2012.
As storm surge is the movement of ocean water above high tide, inundation is the height of water on dry land caused by the surge. The severe effects of storm surge are augmented by the phase of the moon, local tide, and the storm’s extremely low barometric pressures. Each millibar reduction of air pressure will cause the water surface to rise 1 cm. Therefore, the more intense the storm (lower barometric pressure), the greater the storm surge.7 In 1899, Tropical Cyclone Mahina produced a surge of 14.6 meters (approximately 48 feet) with fish and dolphins reportedly found on top of 15-meter cliffs.8 The Galveston, Texas hurricane in the United States that killed 8,000 people in 1900 produced a 5-meter storm surge that flooded the island, which has a maximum height of only 3 meters. In 2005, during Hurricane Katrina, a recorded surge wave averaging 2 meters traveled as far inland as 19 km.
Current State of the Art
Health Consequences and Public Health
Recent large destructive cyclonic storms such as Hurricanes Katrina and Sandy in the United States, as well as Typhoon Nari in Taiwan reaffirm the complex challenge of providing effective public health planning for such events, especially for those with functional or access needs (special populations). Burkle and Rupp stated that disasters, “keep governments and planners honest by defining public health and exposing its vulnerabilities.”9 Noji noted that a variety of public health emergencies share a common theme by negatively impacting the public health environment and its protective infrastructure. Specific vulnerabilities include the provision of water, sanitation, shelter, food, and basic health. It is well-known that poverty and social inequality, environmental degradation from inappropriate land use, and a rapid population growth all contribute to the negative public health effects of a tropical cyclone’s landfall.10
After experiencing a cyclone, levels of resilience to acute and chronic stress and any subsequent catastrophic shock are typically lowered for individuals and groups. An increased risk of susceptibility exists to diseases, both physical and mental. Acutely, the large number of deaths, illnesses, and injuries caused by the cyclone overwhelm the local health services. The destruction of hospitals and clinics by the storm further compromise the immediate medical response and also the provision of long-term care. Depending on the storm’s magnitude, the greatest potential for loss of life does not necessarily come from the actual event, but instead from the subsequent everyday health risks such as reduced access to potable water, failure of sanitation systems, lack of care for medical and psychiatric conditions, and exposure to insect vectors.
The public is generally aware that tropical cyclones are capable of causing devastating damage that can severely cripple, if not destroy, a society and its infrastructure. Yet, it is expected by the effected community, both in the United States and internationally, that established public health and healthcare systems will continue to provide services not only in the days leading up to the storm, but during and after the event as well.11 As a result of these demands, it is imperative that the medical and public healthcare communities are prepared to not only manage injuries caused by the storm, but also to provide continued care for patients with chronic medical conditions and functional or access needs (see Chapter 10). Typically, these include victims with hypertension, diabetes, renal failure requiring dialysis, mental illness, physical disabilities, and cancer receiving chemotherapy. This is in addition to ensuring safe public drinking water, appropriate sewage disposal, control of disease vectors such as mosquitoes and rats, food distribution, and protection of food supplies from contamination (Table 36.4).
Impact of Cyclones and Storm Surges on the Community Components and Indicators of Effects
| Categories of Impact | Components Involved | Indicators of Impact |
|---|---|---|
| Physical | Inadequate physical protection; poor-quality housing and infrastructure; disruptions of communication, roads, utilities, and public works infrastructure | Trauma-related death tolls; damage/loss of property such as infrastructure, homes, industry, animals, and crops; disruption of normal life; migration to safe places; lack of electricity, potable water, and food; accumulation of waste |
| Economic | Loss of livelihood and income opportunities; loss of assets and savings; need for recurrent aid; lower socioeconomic stratification | Low income, poverty, unemployment, landlessness, unequal land distribution, lack of relief and rehabilitation, and forced movement of lower-income populations |
| Agricultural | Land degradation; intrusion of salt water for irrigation increasing seasonal unplanted fields | Low productivity, frequent crop loss, outbreak of migration among the owners of small farms and farm laborers; lack of money for purchasing seed |
| Social | Disintegration of social organization, increased incidence of female-headed households and resource-poor communities; poor educational services | Social/ethnics crisis; social marginalization, violence, and crime; apathetic attitude; identity crisis; plight of people with decreased options for safety and survival |
| Environmental | Land and environmental degradation; deforestation, loss of biodiversity and marine resources, increase in salinity, intrusion of salt water, lowering of water table, increase risk to dams | Deforestation; loss of soil fertility; limited biodiversity; increase in refugees, migrants, and the homeless; rising disaster-related deaths |
| Public Health | Disruptions of healthcare and utility services, inadequate sanitation, lack of qualified physician and clinical services, lack of care for vulnerable groups | Increased mortality and morbidity; poor health and malnutrition; disease epidemics; exacerbation of chronic diseases; increase in PTSD |
Evacuations
Ideally, no one would be physically present to suffer death or injury during the landfall of a devastating tropical cyclone. In fact, due to their well-defined paths of travel and the use of modern meteorological tracking systems, the movement for 70% of hurricanes will be forecasted 24 hours in advance of their approach to land based on their speed and direction during the previous 24–36 hours.12 Based on these predictions, people in vulnerable areas are often asked to evacuate voluntarily while local officials assist by changing traffic flow patterns. Often, the contra flow technique is employed, in which both lanes of a roadway are used for outgoing traffic. Researchers have observed that, depending on local and personal experiences, citizens will engage in two opposing types of behavior prior to an evacuation order. They will either spontaneously self-evacuate or, despite storm warnings and subsequent evacuation orders, refuse to comply and remain in their homes, sheltered in the same way they have done in previous years during storms.13 During Hurricane Sandy, despite strong warnings from emergency management, which included 33,000 telephone calls, use of electronic media and emails, knocking on individual doors, and requesting support from local traditional media sources, thousands of New Yorkers did not evacuate. Data from an official survey conducted by New York City showed that 22% felt that the storm would not be strong enough to pose a danger, 11% felt that their home was high enough to prevent property flooding, and 8% felt there home was structurally sound enough to withstand the storm.14
Evacuation is a very complex undertaking requiring the coordination of multiple unique endeavors, not the least of which is maintaining basic public health services for evacuees. In addition to logistics, cost is an issue. This includes not only the expenses related to the evacuation itself, but also of lost revenue to displaced individuals and to local industry. Therefore, the decision to evacuate an area has significant ramifications.
Hospitals also face the threat of hurricane-induced evacuations. From the years 1971–1999 in the United States, hurricanes prompted more than thirty-eight hospital evacuations.15 Evidence from hospital evacuations after Hurricane Rita suggest it will take an average of approximately 22 hours (range 6–32 hours) to transfer patients out of a facility.16
Many countries other than the United States do not support mass evacuations in the face of a storm. For example, in Taiwan, a community that is frequently subjected to tropical cyclones, most of the buildings are wind-resistant. Only people who live in flood plains, mudslide prone areas, or who are physically disabled or dependent are considered for evacuation.17
The decision to evacuate is based on available resources and an estimate of the resulting economic impact as well as the potential loss of life. Because storm landfall predictions can lead to expensive evacuation preparations and subsequent disruptive population movements, individuals involved in making such decisions must consider the potential negative impacts of an evacuation on commercial, healthcare, and other public health activities. Making the decision to evacuate is a challenge for administrators and community leaders, and involves deciding who should be evacuated, when the evacuation should start, and the logistics for the evacuation. Such logistic considerations include mass transportation, traffic patterns, and provision of control and security. There are four major event outcomes for which the evacuation decision will either enhance or damage the credibility of the decision-makers. These are dependent on what happens during the event itself:18
Evacuation with direct damage to the area or structure evacuated: no lives lost due to the damage nor credibility lost but large economic costs through loss of revenue and expenses incurred.
Evacuation with no damage to the area: no lives lost due to the storm but a loss of credibility with large economic costs through loss of revenue and expenses incurred.
No evacuation with damage to structures and area: even if no lives lost due to the damage, there is a loss of credibility and a large economic cost due to repair and loss of revenue.
No evacuation with no damage to the area in the absence of a direct impact: no lives lost, no credibility lost, and no economic effects.
Research indicates that, once an evacuation decision is made, a considerable amount of time (up to 2 hours using conventional warning practices) may elapse before people in the affected area hear, absorb, and respond to the instructions.19 The time required to accomplish the evacuation once the physical movement of people is underway depends on the characteristics of the area and on the availability of public transportation and large highways (Table 36.5). It is intuitive to believe that a larger population requires a longer evacuation time, but warning and evacuation times do not necessarily increase with population size and density. This is true, in part, because the infrastructure capacity (for example, street systems and public transportation resources) necessary for moving individuals out of the area is generally more extensive in regions with a greater population.20 In areas where a significant reluctance to evacuate exists, the evacuation routes are limited despite the use of contra flow techniques, or population density is high, repeated warnings may be necessary. Characteristics of a good evacuation plan include:
Identification of available resources, such as community faith-based organizations and voluntary medical and fire assets.
Knowledge of vulnerable populations, which would include those who are elderly, ventilator-dependent, and have language barriers.
Awareness of hazardous sites in the area: flood zones, refineries, and hazardous material sites.
Knowledge about main transportation assets: highways, trains, buses, and airports.
Shelter locations and staging areas for evacuation.
Time considerations for phases of evacuation
| Evacuation Phase | Time Needed |
|---|---|
| Reaching an official decision to evacuate | Days |
| Mobilizing community evacuation resources | Hours |
| Communicating appropriate protective action instructions to the public | Hours |
| Individual mobilization of resources to leave the area at risk | Hours to days |
| Completing the physical evacuation of people occupying the affected area | Days |
Mortality
In violent tropical cyclones, almost 90% of all primary weather-related deaths are attributed to drowning from the accompanying storm surge. Examples include the cyclones that affected Bangladesh in 1970 and 1991, the Indian coastal states of Andhra Pradesh in 1977 and Orissa in 1999, the Indian state of Gujarat along its coast facing the Arabian Sea in 1998, and the U.S. state of Mississippi in 2005 (Hurricane Katrina). The other 10% result from tornadoes, flying debris, and collapsing structures.12,21,22 More recently in 2012, Hurricane Sandy on the east coast of the United States caused the direct deaths of more than 147 people, primarily due to storm surge. Almost half of them were more than 65 years of age.14 In Taiwan and many other Asian/Pacific basin countries, mortality numbers due to storm surge and mudslides remain quite high despite warnings. This has been attributed to deforestation, which allows for mudslides and debris to flow through farming communities during the torrential rainstorms that accompany tropical cyclones. Many countries prone to damage from storm surge have installed early warning systems, which if used in conjunction with timely evacuations and storm-resistant sheltering, can achieve a decrease in mortality rates. Prediction and warning systems have been credited with protecting lives in the Mississippi counties of Mobile and Baldwin. Here, computer models predicted a large storm surge 2 days in advance of the hurricane’s arrival, allowing for evacuation and adequate preparation.
In the countries of Bangladesh and Cuba, storm-related mortality rates are lower despite the lack of sophisticated electronic warning systems. This is due to the use of trained volunteers who implement a well-known and easily recognizable flag and siren signal system. When Hurricane Charley struck Cuba, only four deaths occurred despite damages estimated at more than $1 billion USD.23,24 Conversely, simply having the technology will not guarantee a decrease in mortality. This was seen in Haiti during Tropical Storm Jeanne in 2004. The area had a good electronic warning system, but due to a coup earlier that year, there were no emergency managers available to utilize the system and more than 1,000 people died.25 In general, the disparity between developing and developed countries remains significant. In developing countries, the majority of cyclone-related deaths result from storm surge in the impact phase, while in developed countries, mortality has declined markedly. The majority of deaths in developed countries that do result from cyclones occur in the post-impact phase.
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