Climate Class 9 Notes helps students understand the weather conditions and climate patterns of India. Climate refers to the average weather conditions of a place over a long period of time, including temperature, rainfall, humidity, and wind.
This chapter explains the factors influencing India’s climate, such as latitude, altitude, distance from the sea, pressure and wind systems, and ocean currents. The Class 9th Geography Chapter 4 Notes also focus on the Indian monsoon. It plays a major role in agriculture and daily life.
What is Climate?
Climate refers to the total sum of weather conditions over a large area for a long time (more than 30 years). Weather describes the atmospheric state at a specific time. Both share elements like temperature, pressure, and precipitation. This chapter is included in CBSE Class 9 syllabus. It explores India's diverse climate, its influencing factors, and the significance of the monsoon. These Class 9 Climate Notes offer concise information for students.
Climate Class 9 Notes
India's climate depends on many factors. Understanding these elements helps explain various weather phenomena. These Class 9 Climate Notes simplify complex topics.
Climate Controls
Several global factors influence the climate of any place.
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Latitude: Solar energy varies with latitude. Temperatures generally decrease from the equator towards the poles due to Earth's curvature.
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Altitude: As altitude increases, the atmosphere becomes less dense. Temperature decreases with height. This is why hills are cooler.
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Pressure and Wind System: This system relies on latitude and altitude. It impacts temperature and rainfall patterns.
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Distance from the Sea: Coastal areas have moderate climates. Inland areas experience 'continentality' – very hot summers and very cold winters.
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Ocean Currents: Warm or cold ocean currents, with onshore winds, warm or cool coastal areas.
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Relief Features: Mountains can block winds, causing precipitation on one side. High mountains also stop cold or hot winds.
Factors Affecting India's Climate
India’s climate is unique due to its specific geographical features.
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Latitude: The Tropic of Cancer divides India. This gives India characteristics of both tropical and subtropical climates.
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Altitude: Northern mountains protect India from cold Central Asian winds. This leads to milder winters compared to Central Asia.
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Pressure and Winds: India's weather is shaped by surface winds, upper air circulation, and western cyclonic disturbances. Southwest Monsoon winds bring moisture and rainfall. Jet streams are fast, narrow air currents that also affect weather.
Indian Monsoon
The climate of India is greatly shaped by monsoon winds. Monsoon means the seasonal reversal of the wind system.
Mechanisms:
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Differential heating and cooling of land and water. Land heats faster, creating low pressure.
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Shift of the Inter-Tropical Convergence Zone (ITCZ) over the Ganga plains in summer. This is called the monsoon trough.
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Presence of a high-pressure area east of Madagascar.
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Intense heating of the Tibetan plateau creates strong air currents and low pressure.
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Movement of the westerly jet stream north of the Himalayas and the tropical easterly jet stream over the peninsula.
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Southern Oscillation (SO) affects monsoons through changes in Pacific Ocean pressure.
Onset and Withdrawal of Monsoon
The monsoon lasts 100-120 days, from early June to mid-September. The sudden increase in rainfall is called the 'burst' of the monsoon.
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Arrival: Arrives at India's southern tip by early June. It splits into Arabian Sea and Bay of Bengal branches. The Arabian Sea branch reaches Mumbai by June 10th. The Bay of Bengal branch reaches Assam by early June. By mid-July, it covers the entire country.
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Withdrawal: Starts in northwestern states by early September. It completely leaves the northern half by mid-October. By early December, it withdraws from the rest of the country.
The Seasons
India experiences four main seasons with some regional differences. These are important for Class 9 Geography Chapter 4 Notes.
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Cold Weather Season (Winter): Mid-November to February in North India. December and January are coldest. Temperatures decrease from south to north. Clear skies, low humidity, and weak winds are common. This season supports 'rabi' crops.
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Hot Weather Season (Summer): March to May. Rising temperatures and falling air pressure in the north. 'Loo' refers to strong, hot, dry winds. 'Mango showers' are pre-monsoon rains aiding mango ripening.
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Advancing Monsoon (Rainy Season): South-east trade winds, after crossing the equator, enter India as southwest monsoons. They bring widespread rain. Mawsynram gets the highest rainfall. 'Breaks' in monsoon rainfall relate to the monsoon trough's movement.
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Retreating/Post Monsoons (Transition Season): October-November. Clear skies and rising temperatures mark monsoon withdrawal. High temperature and humidity create 'October heat'. Temperatures drop rapidly in North India by late October.
Distribution of Rainfall
Rainfall patterns vary significantly across India.
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Western coast and northeast India receive over 400 cm annually.
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Western Rajasthan and parts of Gujarat, Haryana, and Punjab receive less than 60 cm.
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The interior Deccan plateau and east of Sahyadris also get low rainfall.
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Snowfall is only in the Himalayan region.
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Annual rainfall is highly variable each year.
Monsoon as a Unifying Bond
The monsoon profoundly influences India. Its seasonal rhythm affects agriculture and life. Despite uncertainties, people eagerly await its arrival. Monsoon rains provide water, binding the country by supporting farming activities.
Mechanism of Monsoon
The Indian Monsoon is a complex weather system driven by several interconnected factors.
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Differential Heating: The land heats and cools faster than the sea. In summer, the Indian landmass gets very hot, creating a low-pressure area. The surrounding seas remain cooler, maintaining higher pressure. This pressure difference pulls moisture-laden winds from the sea towards the land.
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ITCZ Shift: The Inter-Tropical Convergence Zone (ITCZ), a low-pressure belt, shifts northward over the Ganga plains during summer. This shift creates a 'monsoon trough' which attracts winds.
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Madagascar High: A high-pressure area east of Madagascar at 20°S in the Indian Ocean strengthens the south-easterly trade winds, pushing them towards India after crossing the equator.
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Tibetan Plateau Heating: Intense heating of the Tibetan plateau during summer generates strong vertical air currents. This forms a high-altitude low-pressure zone, further attracting monsoon winds.
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Jet Streams: The movement of the westerly jet stream north of the Himalayas and the presence of the tropical easterly jet stream over the Indian peninsula in summer influence the timing and strength of the monsoon.
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Southern Oscillation (SO): Changes in pressure conditions over the southern oceans, particularly the tropical eastern Pacific, affect the monsoon's intensity. This is an irregularly periodic variation impacting global climate.