CBSE Class 9 Answered

A brief summary of the main points of this chapter is as follow:

• While weather is a day today state of atmosphere of an area at any given point of time, climate is the sum total of weather conditions of a given place over a longer period of time.
• India experiences monsoon type of climate. Rainfall is uneven and varies from region to region. For example, it rains over 400 cm in Meghalaya, but parts of western Rajasthan experiences only 10 cm of rainfall annually.
•  There are six main factors that affect the climate in India.
• Latitude: Tropic of Cancer, latitude, passes through India at 23°26′N to the north of equator. It passes through eight Indian states running from the Rann of Kutch from Gujarat to Mizoram in the east. The tropic of Cancer divides the country into two halves. The areas in India that lie to the north of the tropic of cancer lies in the sub tropical regions while areas to the south of the tropic lie in the tropical regions. Temperature remains high through out the tropical regions.
• Altitude: As we go above the sea level, the temperature starts declining. Thus temperature decreases with an increase in altitude. There is a decrease of 10C for every 166 m rise in the height. This is the reason that hill stations are cooler than the plain region.
• Air Pressure and Surface Winds: India lies in the region of north easterly winds. However as these winds blow over land, they carry very little moisture and causes no rainfall.
• During winters, high pressure area is created to the north of the Himalayas. Cold winds blow from this region to low pressure areas to south over the oceans.
• Distance from the Sea: While the coastal regions experience moderate type of climate, the region located in the interiors of the continent experience extreme type of climate.
• Ocean Currents and Relief features further affect the climate. For example, high mountains act as a barrier to the moisture laden winds. The latter after striking the former shed its moisture and bring rainfall in the region.
• The Indian climate is affected by the Monsoon winds.
• Jet streams are the narrow belt of high altitude westerly winds in the troposphere. They blow at a fast speed of about 110km/h in summers to about 184km/h in winters.
• The westerly jet streams are responsible for bringing western cyclonic disturbances in north west India resulting in rainfall in winters. The easterly jet stream blowing over north India result in the creation of tropic depressions. The latter play a significant role in the distribution of rainfall in the country.
• It has been seen that apart from other factors, the changes in the pressure conditions over the southern oceans also affect the monsoons. Generally when the tropical eastern south Pacific Ocean experiences high pressure, the tropical eastern Indian Ocean experiences low pressure. However it has been noticed that there has been a reversal in the pressure conditions. While the eastern south Pacific Ocean has low pressure conditions, the eastern Indian Ocean has relatively high pressure conditions. It is this periodic change in pressure conditions is known as the Southern Oscillation or the SO.

The Rainy Season

• Advancing Monsoon:  South West Monsoon winds blow over the warm oceans and thus bear moisture bringing abundant rainfall in India. The monsoon covers the entire country in about a month’s time.
• The arrival of the Monsoon winds brings a change in the weather of the country. Sometimes at the time of arrival, the rainfall increases suddenly which is commonly known as the burst of the Monsoons.
• The western slopes of the Western Ghats receive heavy rainfall from the monsoon winds. Sometimes, there are ‘brakes’ in the monsoon rainfall. Initially at some places, it rains only for few days. While it rains heavily in north eastern parts of the country, Kerala and on the western slopes of the Western Ghats, moderate rainfall is experienced in the south eastern parts of the country and the Indo Gangetic Plains.
• Scanty rainfall is experienced in western parts of Rajasthan, Punjab, Haryana and Gujarat.
• Retreating Monsoon: During October and November, the South West monsoon winds become weaker and start retreating from the by clear skies and the increase in mercury northern plains. The retreat of monsoon is marked level.
• This increase in temperature is termed as ‘October heat’. At this time, the low pressure conditions shift to the Bay of Bengal giving rise to cyclonic depressions.
• These cyclonic depressions often results in the destruction of life and property generally on the eastern coast and the southern coast. Most of the rainfall of the Coromandel Coast is derived from depressions and cyclones.

The Hot Weather Season in India

• India experiences hot weather season beginning from the month of March till the end of May.
• Different regions in India experiences different temperatures according to their latitudinal positions.
• The highest average temperature in March on the Deccan Plateau is about 38⁰C .
• While the states of Gujarat records temperature up to 42⁰C, the north western parts of India experiences temperature up to 45⁰C during the month of May.
• At this time the northern parts of the country experiences decrease in the air pressure due to high temperature.
• One of the striking features of hot weather season in India is the blowing of local hot winds called ‘loo’.
• Loo is a hot dry wind which blows over north and north western parts of India. Direct exposure to this wind may result in fever etc.
•  Dust storms are a common feature in north India. These storms bring some relief to the people from the soaring temperature. Sometimes thunder rain storms also accompany the dust storms resulting in downpour. In Bengal, these rain storms are known as ‘Kaal Baisakhi’.
• In coastal regions temperature remains low as compared to the northern parts of the country. This is because the moderating influence of the sea, which the coastal regions experiences.
• Just towards the end of the summer season, Kerala and Karnataka experiences some light showers which help in the ripening of mangoes. Thus they also referred as ‘mango showers’.

The Cold Weather Season

• The cold weather season in India begins during mid November in Northern India and stays till February. December and January are the coldest months.
•  During the cold season, the days are warm and nights are cold. When temperature decreases, frost is commonly experienced in Northern India.
• The cold season in most parts of the country is the dry season as northeast trade winds blow from land to sea.
• Many cyclonic disturbances occur over northern India during this time.  These results in rainfall during winters and snow fall in the Himalayan regions. This winter rainfall helps in the cultivation of the rabi crops.