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Chapter 27 Waiting for the Rains: The Effects of Monsoons in South Asia. I. Geoterms.
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Chapter 27Waiting for the Rains: The Effects of Monsoons in South Asia
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.
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.
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: smallamount of rain fall in South Asia, dusty fields, and dwindling water sources.
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 can’t hold as much moisture as warm air clouds cross over mountains with little moisture remaining in them.
a. One of the World’s 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 Novemberto April. iii. Tropical cyclones (aka Hurricane) 1. City is lashed by high winds and waves because city is situated at sea level.
b. Life Depends on the Rains i. Bangladesh’s economy depends on agriculture. 1. 3/5th’s 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 city’s 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.
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 TharDesert 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.
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.
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.
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.
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
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. They’ve 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.”
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.
b. Other regions also have monsoons: i. November to April: northern Australia. ii. May to July: West African coast. iii. Middle of summer: Arizona. c. Everywhere: the climate affects human activities.
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.
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.
