Class 9 Geography Chapter 4 Notes - Climate

We study climate to understand the atmospheric conditions prevailing over a particular area, which helps us anticipate seasonal changes and adapt accordingly. This knowledge allows us to prepare for different weather conditions, such as wearing woolen in cold months or expecting rain during certain periods. 

By studying climate, we can better understand and predict weather patterns, ensuring our comfort and safety throughout the year.

Introduction

Weather: It is the state of atmosphere at any point in time and space, it changes every moment.

Example: Cloudy, dry, windy, wet weather

Climate : It refers to the sum total of weather conditions and variations over a large area for a long period of time. It is the sum total of average weather conditions of 30 years.

Example: Monsoon, equatorial desert, cold climate etc.
Climate and Weather Differences

India has Diverse Climatic Conditions

We can take two important elements, Temperature and Precipitation, and examine how they vary from place to place and season to season.

Temperature variations:

• Rajasthan desert: up to 50°C in summer
• Pahalgam, Jammu and Kashmir: around 20°C in summer
• Drass, Jammu and Kashmir: as low as -45°C in winter
• Thiruvananthapuram: around 20°C in winter
• Thar Desert: 50°C in the day, 15°C at night
• Andaman and Nicobar Islands, Kerala: minimal temperature difference between day and night

Different Climatic Zones in India

Precipitation variations:

• Snowfall in the upper parts of the Himalayas
• Rainfall in the rest of the country
• Annual precipitation: over 400 cm in Meghalaya, less than 10 cm in Ladakh and western Rajasthan
• Rainy season: June to September for most parts, October and November for the Tamil Nadu coast
• Coastal areas: less contrast in temperature and seasonal conditions compared to interiors

Climatic Controls

The climate of a place is influenced by various factors that interact to determine its characteristics. These factors include:

• Latitude: Due to the curvature of the earth the amount of solar energy received varies according to latitude, resulting in temperature variations from the equator to the poles. The closer a location is to the equator, the warmer it tends to be.

Latitudes

• Altitude: Higher altitudes have a less dense atmosphere, leading to lower temperatures. As elevation increases, the air becomes thinner, causing a decrease in temperature.
• Pressure and Wind Systems: The distribution of pressure and wind systems across the Earth influences temperature and rainfall patterns. These systems are influenced by factors such as latitude and altitude.
• Distance from the Sea (Continentality): Locations closer to the sea tend to experience more moderate climates due to the moderating effect of the ocean. Greater distance from the sea can result in more extreme weather conditions, with greater temperature variations.
• Ocean Currents: Ocean currents play a role in shaping coastal climates, particularly when combined with onshore winds. Warm ocean currents can lead to milder temperatures, while cold currents can result in cooler climates.
• Relief Features: The presence of relief features, such as mountains, can impact local climates. High mountains act as barriers to winds, forcing them to rise and cool, which can lead to increased precipitation on the windward side. In contrast, the leeward side, sheltered from prevailing winds, tends to be drier.

These factors work together to shape the climate of a region, with each playing a unique role in determining the temperature, precipitation patterns, and overall weather conditions experienced in a particular area.

Factors Affecting India’s Climate

Latitude

• The Tropic of Cancer runs through the middle of India, dividing it into tropical and subtropical regions.
• India is situated roughly between 8^οN and  37^ο N latitudes. 
• India is divided into almost two equal parts by the tropic of cancer. 
• The southern half lies in the tropical zone, and the western half is in the subtropical zone. 
• Therefore, India’s climate has characteristics of tropical as well as subtropical climates.

Altitude

• India has mountains to the north, with an average height of about 6000 meters.
• The Himalayas prevent the cold winds from Central Asia from entering the subcontinent.
• It is because of these mountains that this subcontinent experiences comparatively milder winters than Central Asia.

Pressure and Winds

• India's climate is influenced by atmospheric conditions such as pressure, surface winds, upper air circulation, and cyclonic disturbances.
• India is situated in the path of north easterly winds originating from the subtropical high-pressure belt in the north.
• In India, monsoon winds originate from a high-pressure area north of the Himalayas during winter.
  These winds move towards low-pressure areas over the oceans to the south.
• During summer, a low-pressure area forms over interior Asia and northwestern India. This leads to a reversal of wind direction, bringing moist air from the southern Indian Ocean.
• The Southwest Monsoon winds carry moisture as they blow over warm oceans.
• These winds bring abundant rainfall to the mainland of India.
• The Coriolis force, influenced by the Earth's rotation, causes winds to deflect to the right in the Northern Hemisphere. This phenomenon is known as 'Ferrel's Law'.

The Season

• Cold weather season  --  December to February
• Hot weather season  --  March to May
• Advancing monsoon season  --  June to September
• Retreating monsoon season  -- October and November

The Cold Weather Season (Winter)

• The cold weather season in northern India runs from mid-November to February.
• December and January are the coldest months in the northern region.
• Temperatures decrease from south to north in India.
• Chennai on the eastern coast maintains an average temperature of 24-25°C, while in the northern plains, it ranges between 10°C and 15°C.
• Days are warm, and nights are cold during this season.

• Frost is common in the north, and higher Himalayan slopes experience snowfall.
• Northeast trade winds dominate India during this period.
• India experiences a mostly dry season due to the land-to-sea wind flow.
• Winter rainfall, known as 'mahawat,' is essential for cultivating 'rabi' crops.
• Distinctive feature: influx of cyclonic disturbances from the west and northwest bringing winter rains and snowfall.
• Peninsular India lacks a well-defined cold season due to the moderating effect of the sea.
• India experiences the Advancing Monsoon phenomenon from south to north.
• The monsoon typically reaches Kerala around June 1st and covers most parts of the country by July 15th.
• The Bay of Bengal and the Arabian Sea influence the monsoon's behavior over India.

Hot weather season (Summer)

• During summer in India, the sun moves northward, causing the global heat belt to shift accordingly.
• From March to May, India experiences hot weather due to this northward shift.
• In March, the Deccan plateau records temperatures around 38°C as the highest.
• April sees temperatures of about 42°C in Gujarat and Madhya Pradesh.
• By May, the northwestern parts of the country witness temperatures reaching 45°C.

Atmospheric Conditions over the Indian Subcontinent in the Month of June

• Peninsular India experiences relatively lower temperatures due to the moderating effect of the oceans.
• During the summer months, the northern part of India experiences rising temperatures and falling air pressure.
• By the end of May, a low-pressure area forms from the Thar Desert to Patna and Chotanagpur plateau, initiating air circulation.
• 'Loo' refers to strong, gusty, hot, dry winds prevalent in northern and northwestern India during the day.
• Dust storms occur frequently in May, offering temporary relief by lowering temperatures and sometimes bringing light rain and cool breezes.
• Localized thunderstorms, known as 'Kaal Baisakhi' in West Bengal, are common during this season, accompanied by violent winds, heavy rain, and hail.
• Pre-monsoon showers commonly occur towards the end of the summer season, particularly in Kerala and Karnataka.
• These showers, known as 'mango showers', aid in the early ripening of mangoes.