Chapter 27 Waiting for the Rains: The Effects of Monsoons in South Asia

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Chapter 27Waiting for the Rains The Effects of
Monsoons in South Asia
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I. Geoterms
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• Atmospheric Pressure the weight of the
  atmosphere pressing down on any point of the
  surface of Earth. Air sinks in high-pressure
  areas, and few clouds form. Air rises in
  low-pressure areas to form clouds that produce
  rain.
• Monsoon a seasonal wind. Summer monsoon winds in
  South Asia usually bring rain to that region.
• Orographic effect the precipitation that occurs
  when moist air rises up the side of a mountain.
  As the air rises, it cools down and releases most
  of its moisture as rain or snow.
• Rain shadow a dry area on the downwind side of a
  mountain.

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II. The Geographic Setting
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• a. Changes in Atmospheric Pressure Create
  Monsoons
• i. Falling cool air creates high pressure areas.
• 1. Due to the downward pressure, very little
  surface air can rise into the upper atmosphere to
  form clouds.
• 2. Typically sunny days and no rain.
• ii. Rising warm air creates low pressure areas.
• 1. If the rising air is moist, clouds form
  bringing rain.

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• iii. Wind created when air from high pressure
  areas naturally flow into low pressure areas.
• 1. Spring and Summer
• a. Air over the peninsula of South Asia warms up
  faster than the air over the Indian Ocean. Moist
  air over the Indian Ocean flows into the low
  pressure area created when the hot air rises over
  South Asia.
• i. Air movement result Summer monsoons
• 2. Fall and Winter
• a. Air over South Asia cools down and sinks,
  forming a high pressure area, keeping the moist
  air from the summer monsoons out to sea.
• 1. Result small amount of rain fall in South
  Asia, dusty fields, and dwindling water sources.

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• b. Mountain Ranges Create Rain Shadow
• i. Mountain slope facing
• 1. upwind (against the direction of the monsoon
  winds) generally receives large amount of rain.
• 2. downward (same direction the wind is
  blowing) receives far less rain.
• a. Rain shadow dry area on the downward side.
• ii. Orographic Effect
• 1. Clouds blow up against mountains ? moist air
  rises up along mountain slopes ? air cools as it
  rises ? clouds release moisture as precipitation
  because cooling air cant hold as much moisture
  as warm air ? clouds cross over mountains with
  little moisture remaining in them.

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Orographic Effect
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III. The Wet Months in Dhaka, Bangladesh
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• a. One of the Worlds Wettest Capitals
• i. Most of Bangladesh lies on a river delta that
  rises dangerously high during monsoon rains.
• 1. Result possible flooding causing difficult
  rice cultivation.
• ii. Dhaka
• 1. Located in the center of Bangladesh.
• 2. One of the wettest climates on Earth.
• 3. Up to 80 inches of rain fall each year.
• 4. Most rain during summer months.
• 5. Weather is dry from November to April.
• iii. Tropical cyclones (aka Hurricane)
• 1. City is lashed by high winds and waves because
  city is situated at sea level.

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• b. Life Depends on the Rains
• i. Bangladeshs economy depends on agriculture.
• 1. 3/5ths of the population farm the rich delta
  soil, relying on hopefully consistent monsoon
  rains to water their fields.
• a. If late many crops suffer.
• b. If too much rain, flooding occurs. In Dhaka,
  flooding is an issue.
• i. Planting and harvesting becomes impossible.
• ii. Traffic halts.
• iii. Schools and businesses shut down.
• iv. Floodwaters pollute citys drinking supply,
  encouraging disease to rapidly spread.
• v. Dhaka life lesson rains that bring life to
  local fields can also end life in the city.

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IV. The Dry Months of Jodhpur, India
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• a. A City on the Edge of a Desert
• i. Known as the Blue City because many of the
  houses are painted blue.
• ii. Jodhpur sits at the eastern edge of the Thar
  Desert in northern India.
• iii. Region is leading producer of cattle,
  spices, and grains.
• iv. Typical semiarid climate, with hot, dry
  weather throughout most of the year.
• v. Average yearly rainfall 14 inches
• vi. Summer monsoons bring rain from June to
  September.
• vii. Average temperature stays above 60 degrees.

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The Blue City
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• b. Water is a Critical Resource
• i. 80 of people around Jodhpur are farmers.
• 1. Farming is difficult in this dry region.
• 2. Farmers depend on monsoons for water.
• 3. If too little water, crops fail and drinking
  water is in short supply.
• 4. When food runs out, some families survive by
  eating samas, a wild grass. Disease spreads
  easier when people are weak from hunger.
• ii. The people of Jodhpur have adapted to their
  climate.
• 1. They raise livestock capable of surviving on
  native plants when crops fail.
• 2. Farmers use drip irrigation (drip water
  directly onto roots) to conserve water.

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V. Waiting for the Rains in Calcutta, India
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• a. Wet Summers and Dry Winters
• i. 15 million residents. 1/3 live in slums.
• ii. Winters dry and pleasant. Moderate winds
  blowing from the North.
• iii. June to September winds shift directions.
  The moist monsoon air blows in from the Indian
  Ocean.
• 1. Monsoons can dump approximately 50 inches on
  Calcutta in four months. 100 degree days
  accompany the rain.

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• b. Monsoon Rains Begin and End Life
• i. Rain floods the city but they are welcomed by
  farmers and people desiring relief from the
  sticky summer heat.
• ii. Previously, a system of canals drained
  floodwater out of Calcutta. System was abandoned
  for modern streets and sewers. When too much
  rain falls, garbage clogs the old canals,
  standing water in the flooded streets breeds
  mosquitoes, and the mosquitoes spread disease
  (ex malaria). Now, efforts are being made to
  repair sewer lines, clear debris from the river,
  and look at options for rebuilding antiquated
  canals.

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VI. Living in the Rain Shadow Pune, India
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• a. A Year-Round Dry Climate
• i. Pune is located in a rain shadow on the
  downwind side of the Western Ghats. The city
  gets 29 inches of rain annually. Most of the
  year, the air is dry and pleasant. The monsoons
  bring welcome rains from June to September.

The Western Ghats
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• b. Limited Water Makes Water Precious
• i. Instead of planting sugar cane (requires lots
  of water), they now grow more drought resistant
  crops (ex sugar beets).
• ii. Theyve tried increasing rainfall with cloud
  seeding scattering chemicals (silver iodide or
  dry ice) into clouds in order to encourage
  condensation. Rain falls when water vapor in
  clouds condenses into droplets, forming around
  tiny specks of ice in the air. When cloud
  seeding, one hopes that water droplets form
  around the seeds.

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VII. Beginning to Think Globally
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• a. South Asia
• i. Monsoons affect the climate of South Asia.
• ii. Differences in atmospheric pressure between
  the land and sea cause the Summer Monsoons
  bringing welcome rain and deadly floods to
  coastal cities.
• iii. The orographic effect shapes the climate of
  South Asia.

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• b. Other regions also have monsoons
• i. November to April northern Australia.
• ii. May to July West African coast.
• iii. Middle of summer Arizona. (from the Gulf of
  Mexico)
• c. Everywhere the climate affects human
  activities.

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VIII. Global Connections
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• a. How might climate affect the type of housing
  people build?
• i. Hot and humid tropical climates build homes
  that allow breezes to flow through.
• ii. Dry desert climates build small windows to
  keep out the sunlight.
• iii. Very hot climates build houses elevated on
  stilts to avoid flood waters.
• iv. Tundra climates build elevated houses
  allowing cold air to flow underneath the
  buildings. Otherwise, the warmth could melt the
  permafrost (permanently frozen ground) and the
  house would sink into the mud.

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• b. How might climate affect the type of clothing
  people wear?
• i. Arid climates loose-fitting, flowing clothes.
  Also, it covers a significant portion of the
  body to avoid skin exposure.
• c. How might climate affect what people do for
  fun?
• i. Alaska dog sledding and ice fishing are
  common cold-climate sports.
• ii. Hawaii surfing.
• iii. North Africa camel racing.
• iv. Namibia sandboarding on the dunes in the
  Namib Desert.

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Climate Zones Around the World