CSULA - Geology: Severe Weather, Hurricanes and Flooding in Developing Nations

Severe Weather, Hurricanes and Flooding in Developing Nations

Introduction
- Solar Heating and Latitude
  - Equator
    - Sunlight hits the Earth directly
    - Sunlight is concentrated over a small area
    - Less light is reflected
    - Region is much warmer
  - Mid-latitudes
    - Sunlight hits the Earth at a slight angle
    - Amount of sunlight varies with the season
    - Amount of light reflected also varies with season
    - As does the temperature
  - Polar regions
    - Sunlight hits the Earth at a low angle
    - Sunlight is spread out over a greater area
    - More light is reflected
    - Region is much colder
- Solar Heating and the Seasons
  - - Earth’s axis is tilted ~23 ½º
    - Seasons occur due to variations in the amount of incoming solar energy as the Earth rotates

Relationship of sun angle and solar radiation received on Earth
Solar Heating and Atmospheric Circulation
- Air at high elevations:
  - Cooler
  - Expands
  - Water vapor tends to condense
- Air at sea level:
  - Warmer
  - More compressed
  - Can hold more water vapor
Air Circulation & Convection Currents
- Solar Energy Input
  - At the equator - Amount of solar energy received is greater than the amount that is reflected back into space
  - At the poles - Amount of solar energy received is less than the amount that is reflected back into space
  - Need global air and water circulation to balance things
- Air Circulation
  - Through the atmosphere
    - Air warms, expands, becomes less dense and rises up into the atmosphere
    - Air cools, condenses, becomes more dense, and falls down to the surface
    - Called a convection current
  - At the Earth’s surface
    - Warm air at the tropics rises into the atmosphere and moves to the poles
    - Once at the poles, air cools, condenses, sinks to the Earth’s surface, and moves towards the tropics
    - Does not take the Earth’s rotation into account
  - Rotation of the Earth deflects moving air or water away from initial course
  - Called the Coriolis Effect after Gaspard Gustave de Coriolis
Atmospheric Circulation & Convection Cells
- Earth spins at a steady rate, but the actual velocity of any point varies with latitude.
- Effect on Atmospheric Circulation Cells
  - Convection cells still occur but are deflected
    - To the right in the northern hemisphere
    - To the left in the southern hemisphere
- Six Cell Circulation Model
  - Similar to convection current model
  - Six Cells
    - Hadley cells are tropical cells found on each side of the equator.
    - Ferrel cells are found at the mid-latitudes.
    - Polar cells are found near the poles
Global Wind Patterns
- Fronts
  - Different air masses do not mix
  - Boundaries called “fronts”
  - Cold air over warm = unstable
Rotating Air Bodies
- Low Pressure Zone Formation
  - Warm air rises
  - Creates a low pressure zone
  - At the Earth’s surface, air “feeds” the low pressure zone, moves counterclockwise
- High Pressure Zone Formation
  - Cool air sinks
  - Creates a high pressure zone
  - At the Earth’s surface, winds blow clockwise
Rotating Air Bodies
- Bends in the polar jet create troughs and ridges
- Forms cyclones and anticyclones
- Cyclones
  - Low pressure zone in polar jet trough
  - Winds at surface flow counterclockwise towards the core
  - Air is updrafted and cooled
  - Forms clouds, rain and upper level outflow of air
- Anticyclones
  - High pressure zone at ridge of polar jet
  - Air converges in upper atmosphere
  - Descends towards the ground
  - Flows outward at surface
  - Dry, windy conditions
- Cyclonic and anticyclonic winds in the Northern Hemisphere
- Cold Fronts and Warm Fronts

Severe Weather
- Thunderstorms
- Snow / Rain storms
- Mid-latitude cyclones
- Blizzards
- Tornadoes
- Tropical cyclones
  - Typhoons in the western Pacific
  - Cyclones in the Indian Ocean
  - Hurricanes in the U.S.
- Hurricanes
  - How a Hurricane Works
    - Tropical disturbance
      - Low pressure zone develops and draws in clusters of thunderstorms and winds
    - Tropical depression
      - Surface winds strengthen, move about the center of the storm
      - Central core funnels warm moist air up towards stratosphere
      - Air cools, vapor condenses, latent heat released
      - Fuels more updrafts, cycle repeats, storm grows
    - Tropical Storm
      - Storm has sustained surface wind speeds of +39 mph
    - Hurricane
      - Surface winds consistently over 74 mph
      - The Eye
        
        As wind speed increases, winds are spiraled upwards prior to reaching the center
        
        A distinctive clear “eye” is formed
        
        Strongest winds are located on the walls of the eye
      - Hurricane Wind Patterns
Cyclones and The Bay of Bengal
- NOTE:
  - The North Indian Ocean is the only area of the world where tropical cyclones are not given names.
  - However, the Joint Typhoon Warning Center in Hawaii gives identifiers to all tropical cyclones and this one was designated as "05B".
- Bangladesh
  - Climate: Tropical
    - mild winter (October to March);
    - hot, humid summer (March to June); humid,
    - warm rainy monsoon (June to October)
  - Terrain:
    - most of the country is situated on deltas of large rivers
    - About 6% of the total land area is permanently under water, and two-thirds is flooded for part of the year.
  - Environment - current issues:
    - severe overpopulation;
    - many people are landless and forced to live on and cultivate flood-prone land;
    - water-borne diseases prevalent in surface water;
    - water pollution, especially of fishing areas, results from the use of commercial pesticides;
    - ground water contaminated by naturally occurring arsenic
  - Has one of the worst records for natural disasters
    - Floods, cyclones, tidal surges, tornadoes, droughts and even cold spells.
    - 1971
      - Over 1,000,000 people dead
      - country's entire infrastructure on the south coast was wiped out.
    - 1991
      - Cyclone killed nearly 140,000 people, most of them women and children.
      - Casualty rate was lower principally because the government had embarked on an extensive program of cyclone
      - shelter construction which continued until the early 1990s.
- The Indian “Super Cyclone” 1999
  - Hit the Indian state of Orissa hardest
    - Indian officials state that “development in the state has been set back an entire generation”
    - Orissa is one of India’s poorest states
      - India's highest infant mortality rate
      - 2/3 of the rural population living in abject poverty
      - lowest number of doctors per capita
      - Lack of electricity and water
      - < 5% of the population has access to subsidies for food and fuel aimed at poverty-alleviation.
  - Life cycle of the cyclone:
    - 24 October: An area of disturbed weather formed in the Gulf of Thailand.
    - 25 October: This disturbance moved northwestwards across the Malay peninsula into the Andaman Sea.
    - 26 October: A tropical storm formed (winds greater than 39 mph) as the cyclone continued to move into the Bay of Bengal.
    - 27 October: The cyclone gained hurricane/typhoon strength & continued to move northwestwards towards India.
    - 29 October: Sustained winds peaked at an estimated 160 mph as the cyclone made landfall over the Indian state of Orissa.
    - 30 October: The cyclone started to weaken, but slowed and began to drift south back out to sea.
    - 01 November: The cyclone weakened to a depression as it continued its drift southwards just off the coast.
  - Most of the damage caused by
    - Storm surge
    - Heavy rainfall
    - Flooding
  - The Human Cost
    - As of 10th November 1999 the death toll was estimated at 7,500, but expected to rise to near 10,000.
    - Over ten million were affected by the cyclone of which at least a million have been made homeless.
Floods
- Recurrence Interval
  - Time between floods of the same magnitude
    - Example: there is 1 in 100 chance that a peak flow of a certain amount (say, 30,000 cf/s) can occur on a river.
    - Thus, that river is said to have a 100-year interval
- Types of floods
  - Flash Flooding In Arroyos/washes
    - Typically caused by:
      - Intense rainfall
      - Short period of time
      - Topography, soil conditions, and ground cover also important
    - Damage:
      - Roll boulders
      - Tear out trees
      - Destroy buildings and bridges
      - Scour out new channels
      - Landslides
    - How can a foot or two of water cost you your life?
  - River (Regional) Flood
    - Can take several days to develop
    - Can last for a week or more
    - Causes:
      - Seasonally when winter or spring rains, coupled with melting snows, fill river basins with too much water, too quickly.
      - Torrential rains from decaying hurricanes or tropical systems can also produce river flooding.
    - Upstream vs. Downstream Floods
      - Upstream floods
        
        generally local in extent & short lag times.
        
        result from intense storms of short duration.
      - Downstream floods
        
        regional in extent & longer lag times
        
        higher peak discharges.
        
        Result from regional storms of long duration or extended periods of above-normal precipitation.
  - Coastal Flood
    - Often caused by storm surges.
    - Can also be produced by sea waves called tsunamis
  - Urban Flood
    - Roads and parking lots prevent infiltration of water
    - Urbanization increases runoff 2 to 6 times over what would occur on natural terrain.
    - Streets can become swift moving rivers, can flood homes and businesses
  - Ice Jam
    - Floating ice can accumulate at a natural or man-made obstruction and stop the flow of water.
  - Dam Failure
    - Catastrophic failure of a dam can release millions of gallons of water
- General statistics
  - There were 2,200 water-related disasters from 1990 to 2001.
    - Floods: 50%
    - Water-borne and vector disease outbreaks: 28%
    - Droughts: 11%
    - Landslide and avalanche events: 9%
    - Famine: 2%
  - Floods account for 15% of all deaths related to natural disasters, famines for 42%.
  - Approximately 66 million people suffered flood damage from 1973 to 1997.
  - Between 1987 and 1997, 44% of all flood disasters affected Asia, claiming 228,000 lives (roughly 93% of all flood-related deaths worldwide).
  - Economic losses for the region totaled US$136 billion.
  - More than 2,200 major and minor water-related disasters occurred in the world between 1990 and 2001. Asia and Africa were the most affected continents, with floods accounting for half of these disasters. (source: http://www.unesco.org/water/wwap/facts_figures/managing_risks.shtml)
Mozambique
- Climate:
  - tropical to subtropical
- Terrain:
  - mostly coastal lowlands
  - uplands in center
  - high plateaus in northwest
  - mountains in west
- Natural hazards:
  - Severe droughts
  - Devastating cyclones and floods occur in central and southern provinces
- Environment - current issues:
  - A long civil war and recurrent drought in the hinterlands = increased migration of the population to urban and coastal areas
- Pre 2000
  - Drought conditions
  - Was one of Africa's emerging success stories.
    - 10% growth in recent years
    - 1999 was the first since its ruinous civil war that it had not needed to ask for food aid.
- Cyclones and flooding in 2000-2001
  - February 9 – heavy rains & flooding
  - February 22 – tropical Cyclone Eline
  - March 2 –
    - Floodwaters have risen to 8 m (26 feet) in five days
    - 100,000 people need to be evacuated and around 7,000 are trapped in trees
  - Effects in the "cimento" (rich) areas
    - Landslides block streets
    - Streets covered with potholes and sinkholes
    - Telephones/communications disrupted
    - Water service disrupted & water quality impaired
    - Most problems fixed in about a month
  - Effects in the "bairros" (poor) areas
    - Streets destroyed or full of large potholes
    - Hundreds of reed and mud homes underwater
    - Thousands of people left homeless
    - Water quality not restored.
    - Most problems still evident a month later
  - The United Nations estimates 650 people died, more than 500,000 were left homeless, and 2 million people suffered severe economic hardship.
- 2003
  - Cyclone Delfina killed 47 people and displaced 200,000
  - Cyclone Jephat killed at least 11 people a month later

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