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Chapter – 4 Climate class 9 Notes Geography PDF Download

Introduction

  • The climate of a place is defined as the average weather conditions over a thirty-year period. 
  • The state of the atmosphere over a certain area at any given time is referred to as weather. 
  • The elements of weather and climate are temperature, air pressure, wind, humidity, and precipitation. 
  • The basis for dividing the year into seasons — summer, winter, or rainy — is determined by generalised monthly atmospheric conditions. 
  • The climate of India is monsoon-like. 
  • Monsoon is a seasonal wind reversal that occurs throughout the year. 
  • The temperature varies dramatically from one place to the next. 
  • The type of precipitation, as well as its amount and distribution, varies from one section of India to the next. 
  • Temperature differences are less noticeable at the coast. It's the case.

Climatic Controls

  • The interplay of latitude, altitude, distance from the sea, pressure and wind system, ocean currents and relief features determine climatic conditions of a place.

Factors Affecting India’s Climate

  • Indian climate is influenced by latitude, altitude, pressure, and winds. From the Rann of Kuchchh to Mizoram, the Tropic of Cancer runs through the heart of the country. 
  • From the equator to the poles, the air temperature normally drops. As one ascends from the earth's surface to greater altitudes, temperature and air pressure drop. 
  • The Himalayas block central Asian cold winds from accessing the subcontinent. 
  • Various atmospheric factors, such as pressure and surface winds, upper air circulation, western cyclonic disturbances, and tropical cyclones, influence India's climate and weather.
  • The sea has a cooling effect on the climate. Extreme weather conditions are experienced by people who live far from the shore. This is referred to as 'continentality.' 
  • The climate of coastal locations is also affected by ocean currents. 
  • The Coriolis Force is an apparent force created by the earth's rotation. 
  • The direction of the wind changes with the seasons. In the winter, they are damp from north to south, while in the summer, they are exactly opposite, bringing moisture. 
  • In the troposphere, jet streams are thin belts of high-altitude (over 12,000 m) westerly winds. 
  • The westerly flow from the Mediterranean region brings in the western cyclonic disturbances, which are weather phenomena that occur during the winter months.

The Indian Monsoon

  • The climate of India is strongly influenced by monsoon winds.
  • The Arab traders who noticed these winds named it as monsoon.

Following facts are important to understand mechanism monsoons:

  • The differential heating and cooling of land and water.
  • The Inter Tropical Convergence Zone (ITCZ) is a broad trough of low pressure in equatorial latitudes where the northeast and the southeast trade winds converge.
  • The presence of the high pressure area, east of Madagascar.
  • The intense heating of Tibetan plateau during summer.
  • The movement of the westerly jet stream to the north of the Himalayas and the presence of of the tropical easterly jet stream over the Indian peninsula during summer.
    • Apart from his changes in the pressure conditions over the southern oceans also affect monsoon.
    • The periodic change in pressure conditions known as ‘Southern Oscillation’ or SO affects monsoon too.
    • El Nino is a warm ocean current that flows past the Peruvian coast in place of the cold Peruvian current, every 2 to 5 years.

The Onset of the Monsoon and Withdrawal

  • The monsoon are pulsating winds affected by different atmospheric conditions encountered by it, on its way over the warm tropical seas.
  • Monsoon arrives at the southern tip of the Indian peninsula generally by first week of June.
  • Sudden increase and continuation of the monsoon for several days is called as ‘burst’.
  • The Arabian Sea and the Bay of Bengal branches of the monsoon merge over the north western part of the Ganga plains.
  • The withdrawal or the retreat of the monsoon is a more gradual process which begins in the northwestern states of India by early September.
  • The retreating monsoon or the transition season sees the change from hot rainy season to dry winter conditions.
  • The low pressure conditions over northwestern India get transferred to the Bay of Bengal by early November causing cyclonic depressions originating over the Andaman Sea.

Distribution of Rainfall

  • Owing to the nature of monsoons, the annual rainfall is highly variable from year to year.
  • Areas of high rainfall are liable to be affected by floods while areas of low rainfall are drought prone.

The Seasons

  • The cold weather season, the hot weather season, the advancing monsoon, and the retreating monsoon are the four main seasons of India, with minor regional variations. 
  • Northeast trade winds prevail over India throughout the winter season. The days are hot and the nights are chilly. 
  • Frost is widespread in the north, while snowfall is common on the Himalayan higher elevations. 
  • The northern areas of the country face rising temperatures and declining air pressure throughout the summer months. 
  • The strong, gusty, hot, dry winds known as loo that blow during the day over north and northwestern India are a notable element of the hot weather season.
  • The north-western area of the country receives the most rainfall as the monsoon approaches, i.e. during the rainy season. 
  • Dust storms are widespread in northern India. 
  • Localized thunderstorms with strong gusts and torrential downpours, which are frequently accompanied by hail. They are known as 'Kaal Baisakhi' in West Bengal. 
  • The monsoon, which begins in June and lasts for a month, covers the majority of the Indian Peninsula and the central part of the country. 
  • The monsoon has 'breaks' in its rainfall, resulting in wet and dry periods. 
  • The intensity, frequency, and duration of the dry and wet episodes alternate, creating major floods in some areas and droughts in others. 
  • The monsoon had left the Northern Plains by the beginning of October. Due to the high temperature and humidity, the weather becomes unpleasant at this time.

Monsoon as a Unifying Bond

  • The dependence of farmers on rain, a change in seasonal cycle, variance in temperature, the needs of humans, plants and animals, festival dates etc., all depend on monsoon in India. In this way monsoon is a unifying bond for Indians.
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FAQs on Chapter – 4 Climate class 9 Notes Geography

1. What is climate?
Ans. Climate refers to the average weather conditions that prevail in a region over a long period of time. It is determined by factors such as temperature, precipitation, humidity, wind, and atmospheric pressure.
2. What is the difference between weather and climate?
Ans. Weather refers to the short-term atmospheric conditions of a specific place at a particular time, while climate is the long-term average of weather patterns in a particular region or area.
3. What are the main factors that influence climate?
Ans. The main factors that influence climate include latitude, altitude, distance from the sea, ocean currents, prevailing winds, and topography.
4. What are the five main climate types?
Ans. The five main climate types are tropical, dry, temperate, continental, and polar. Each climate type is characterized by different temperature and precipitation patterns.
5. How does climate change affect the environment and human life?
Ans. Climate change can have adverse effects on the environment and human life, such as rising sea levels, extreme weather events, loss of biodiversity, and impacts on agriculture and food security. It can also lead to health problems, displacement of people, and social and economic disruptions.
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