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Natural Hazards
NGSS Performance Expectations
Clarification Statement: Examples of design solutions to weather-related hazards could include barriers to prevent flooding, wind-resistant roofs, and lightning rods.
Ocean Literacy Principles
Table of Contents
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Natural Hazards
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Fig. 1. A tsunami evacuation sign guides people on a safe route to avoid danger in case of a tsunami.
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Image courtesy of Flikr
Natural processes can cause sudden or gradual changes to Earth’s systems, some of which may adversely affect humans. Through observations and knowledge of historical events, we know where some hazards—such as earthquakes, tsunamis, volcanic eruptions, severe weather, floods, and coastal erosion— are likely to occur. Although humans cannot eliminate natural hazards, we can take steps to reduce hazard impacts (Fig. 1). For example, satellite monitoring of weather patterns, along with measurements from land, sea, and air, can help identify and forecast severe weather. In addition, homes and buildings can be designed and built to be resilient to weather related hazards.
Tropical Cyclones
A tropical cyclone is a rapidly rotating storm system characterized by a low-pressure center, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain or squalls over warm waters. There are three types of tropical cyclones, which are characterized by the speed of their sustained wind: tropical depressions, tropical storms, and hurricane (see table below).
| Type of Tropical Cyclone | Description |
|---|---|
| Tropical Depression | A system of clouds and thunderstorms with a defined circulation and maximum sustained winds of less than 39 mph. |
| Tropical Storm | A system of strong thunderstorms with defined circulation and maximum sustained winds of 39-73 mph. |
| Hurricane | A system of strong thunderstorms with well-defined circulation and maximum sustained winds higher than 73 mph. |
Hurricanes
Hurricanes are a type of tropical cyclone that is accompanied by thunderstorms and counterclockwise wind circulation (in the Northern Hemisphere). The winds revolve around an eye (Fig. 2). The processes that cause a tropical cyclone to form and subsequently strengthens into a hurricane depend on at least three conditions:
- A pre-existing disturbance with thunderstorms
- Warm (at least 79 degree F) ocean temperatures to a depth of about 150 feet
- Light upper level winds that do not change much in direction and/or speed throughout the depth of the atmosphere (low wind shear)
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Fig. 2. Hurricane Madeline tracked towards Hawai'i in August 2016, but weakened before making landfall, causing very little damage.
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Image courtesy of NOAA
Hurricane Formation
In the early stages of hurricane formation, the system appears on satellite images as relatively unorganized clusters of thunderstorms. The winds near the ocean's surface then begin to spiral into the thunderstorms' low pressure area, generating heat and energy. The warm ocean water adds moisture and heat to the cooler air, which then rises. As the moisture condenses into drops, more heat is released, contributing additional energy to drive the storm. Bands of thunderstorms then form, and the storm’s clouds rise higher into the atmosphere. If weather and ocean conditions continue to be favorable, the storm system can strengthen and become a tropical depression (winds less than 39 mph or 33 kt). At this point, the storm begins to take on the familiar spiral appearance caused by the flow of the winds and the rotation of the earth. If the storm continues to strengthen to tropical storm status (winds 39-73 mph), the bands of thunderstorms will contribute even more heat and moisture to the storm. The storm becomes a hurricane when winds reach a minimum of 74 mph. At this time, the cloud-free hurricane eye typically forms. The eye is caused by rapidly sinking air at the center, which dries and warms the area.
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Fig. 3. This diagram shows the structure of a hurricane and the dynamics of the rising warm air and falling cool air.
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Image courtesy of Kelvinsong, via Wikimedia
| Naming of Tropical Cyclones |
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Tropical cyclones are called different things depending on where they occur in the world:
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Protecting Against Natural Hazards
Understanding natural hazards can help people prepare for and respond to them. In areas where hurricanes form, for example, people may design and engineer buildings and homes to be resilient to strong winds, flooding, and other storm damage.
In Hawai‘i, there are many different types of natural hazards. Some examples include: floods, fire, landslides, earthquakes, coastal erosion, and sea-level rise. High winds and large waves from tsunamis and hurricanes are the most damaging types of hazards in Hawai‘i. The attachment below gives a detailed guide to protecting your home:
Roof Design
Roofs help to protect and insulate buildings. Roof design is an important element in protecting homes and buildings from natural hazards. Around the world, roofs are built in many shapes and styles. Often, the style depends on culture, exposure to elements (such as rain, snow, wind, and sunlight), cost, and available materials (Fig. 4). The angle of the roof, the number of sides, the shape, and the overhang all affect its performance.
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Fig. 4. Clockwise from top left: A living grass roof in Norway. A stone roof in India. A round roof in Taiwan. Steep, tile roofs in Northern Europe.
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Images courtesy of Nickenge (top left), Biswarup Ganguly (top right), Meiguoren (bottom right), Väsk (bottom left).
Tying the house roof to the foundation helps to strengthen the structure. The ties stop the roof from flying off during high winds. Tie-downs can be added as the home is being built. Tie-downs can also be used to retro-fit older homes to make them more storm-resistant (Fig. 5). Tie downs are often called hurricane clips or hurricane ties.
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Fig. 5. Left to right: Hurricane clips (circled) helped keep the roof on this home during Hurricane Katrina. Hurricane ties are already in place at the top of the wall, even as the roof is being built.
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Images courtesy of William Dryden/FEMA (left) and US. Army: Habitat for Humanity home 2010 (right).
Elevated Homes
Water is responsible for 90% of the deaths caused by hurricanes. Interactive storm surge maps from NOAA help to show areas of flooding vulnerability. Elevated homes have been a useful building design for 1,000s of years to help protect against flooding, water damage, and outdoor pests (Fig. 6). Elevation can also help protect against erosion and unstable ground (Fig. 7).
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Fig. 6. From left to right: Summer homes of indigenous Kamchatka Peninsula people. A modern stilt house in cambodia.
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Images courtesy of S.P. Krasheninnikov (left) and Cam42.
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Fig. 7. Stilt homes on the water in Indonesia. Image copyright and source
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Image courtesy of picasaweb.
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Useful Links
This site has science, teaching, and hurricane forecast links.
This National Marine Educators Assoication (NMEA) resource on BRIDGE uses ocean observing to investigate coastal storms (activity designed for 9-12th grade).
