NCERT Notes Class 9 Geography: Climate Class 9 Geography Notes are important for CBSE board exams of Class 9 students. You’ll learn about climate and what factors affect it, like how high or low a place is, how close it is to the sea, and even how the wind blows.
These notes are important for Class 9 students studying geography because they cover important topics that they need to know for their exams.
Introduction
Climate is the overall pattern of weather conditions in a particular area over a long period of time, usually more than thirty years.
Weather, on the other hand, is the current state of the atmosphere at a specific point in time.
The elements of weather and climate are the same i.e.
- Atmospheric pressure
- Wind
- Humidity
- Precipitation
Climatic Controls
There are six main factors that control the climate of a place: latitude, altitude, pressure, and wind systems, distance from the sea (continentality), ocean currents, and relief features.
- Latitude: The amount of solar energy received varies with latitude due to the curvature of the Earth. Generally, temperatures decrease from the equator towards the poles.
- Altitude: As one goes higher above the Earth’s surface, the atmosphere becomes less dense and temperature decreases. Therefore, higher altitudes, such as hills, tend to be cooler during summers.
- Pressure and Wind Systems: The pressure and wind systems of an area are influenced by its latitude and altitude, which in turn affect temperature and rainfall patterns.
- Distance from the Sea (Continentality): The sea has a moderating influence on climate. Areas farther from the sea experience more extreme weather conditions, with hotter summers and colder winters, known as continentality.
- Ocean Currents: Ocean currents, along with onshore winds, impact the climate of coastal areas. Warm or cold ocean currents flowing past a coastal area can warm or cool the climate.
- Relief Features: Relief, such as mountains, plays a significant role in determining climate. High mountains act as barriers for cold or hot winds and can cause precipitation if they intercept rain-bearing winds. The leeward side of mountains tends to be relatively dry.
Factors affecting India’s Climate
Here are the factors that affect India’s Climate:
Latitude: India’s location between the Tropic of Cancer and the subtropics influences its climate. The southern part, below the Tropic of Cancer, falls in the tropical zone, while the northern part lies in the subtropical zone. Therefore, India experiences characteristics of both tropical and subtropical climates.
Altitude: The presence of mountains in the north, particularly the Himalayas with heights averaging about 6,000 meters, affects India’s climate. These mountains act as a barrier, preventing cold winds from Central Asia from entering the subcontinent. As a result, India has milder winters compared to central Asia.
Pressure and Winds: India’s climate is influenced by various atmospheric conditions, including pressure and surface winds. The northeast monsoon winds originate from the subtropical high-pressure belt in the northern hemisphere. They blow southwards, carrying little moisture as they pass over land, resulting in minimal rainfall.
However, during winter, a high-pressure area develops north of the Himalayas, causing cold dry winds to blow towards low-pressure areas over the oceans. In summer, a low-pressure area forms over interior Asia and northwestern India, leading to the reversal of wind direction. Warm, moisture-laden southwest monsoon winds blow over the warm oceans, bringing widespread rainfall to mainland India.
The Indian Monsson
The climate of India is heavily influenced by monsoon winds, which are seasonal reversals of the wind system. These monsoons occur in the tropical area roughly between 20° N and 20° S. Here are some key facts to understand how monsoons work:
- Differential heating and cooling of land and water create low pressure over the landmass of India, while the surrounding seas experience comparatively high pressure.
- The shift of the Inter-Tropical Convergence Zone (ITCZ) over the Ganga plain in summer, known as the monsoon trough, is a significant factor during the monsoon season.
- The presence of a high-pressure area east of Madagascar, around 20°S over the Indian Ocean, also influences the Indian Monsoon.
- During summer, the Tibetan plateau becomes intensely heated, leading to strong vertical air currents and the formation of low pressure over the plateau at about 9 km above sea level.
- The movement of the westerly jet stream to the north of the Himalayas and the presence of the tropical easterly jet stream over the Indian peninsula during summer also impact the Indian Monsoon.
- Changes in pressure conditions over the southern oceans, along with irregularly periodic variations in winds and sea surface temperatures over the tropical eastern Pacific Ocean, known as the Southern Oscillation or SO, also affect the monsoons.
The Onset of the Monsoon and Withdrawal
The onset and withdrawal of the monsoon are crucial events that mark the seasonal changes in India’s climate. Here’s a breakdown of these phases:
Onset of the Monsoon:
- The monsoon lasts between 100-120 days, spanning from early June to mid-September.
- Upon its arrival, there is a sudden increase in rainfall over several days, known as the “burst” of the monsoon.
- Arrival of the Monsoon in Different Parts of India:
- The monsoon usually reaches the southern tip of the Indian peninsula by the first week of June.
- It then progresses into two branches: the Arabian Sea branch and the Bay of Bengal branch.
- The Arabian Sea branch reaches Mumbai around the 10th of June, while the Bay of Bengal branch arrives in Assam in the first week of June.
- By mid-June, the Arabian Sea branch covers Saurashtra-Kuchchh and the central part of the country.
- The Arabian Sea and Bay of Bengal branches merge over the northwestern part of the Ganga plains.
- Delhi experiences monsoon showers from the Bay of Bengal branch by the end of June.
- By the first week of July, western Uttar Pradesh, Punjab, Haryana, and eastern Rajasthan receive the monsoon.
- By mid-July, the monsoon extends to Himachal Pradesh and the rest of the country.
Withdrawal of the Monsoon:
- The withdrawal of the monsoon commences in the northwestern states of India by early September.
- By mid-October, the monsoon withdraws completely from the northern half of the peninsula.
- The withdrawal progresses from north to south, occurring from the first week of December to the first week of January.
- By early December, the monsoon retreats from the rest of the country, marking the end of the rainy season.
The Seasons
4 main seasons can be identified in India:
- The cold weather season (Winter)
- The hot weather season (Summer)
- The advancing monsoon (Rainy Season)
- The retreating monsoon with some regional variations (Transition Season)
The Cold Weather Season (Winter)
- Winter starts around mid-November in northern India and lasts till February.
- December and January are the coldest months in the northern region.
- Temperatures decrease from south to north.
- Days are warm, but nights can be cold.
- The weather is characterized by clear skies, low temperatures, and low humidity, with light, variable winds.
- This season is crucial for cultivating “rabi” crops.
The Hot Weather Season (Summer)
- From March to May, India experiences a hot weather season.
- Temperatures rise during the summer months, especially in the northern part of the country.
- The “loo,” strong, gusty, hot, dry winds blow over north and northwestern India during the day.
- Pre-monsoon showers occur towards the end of the season, aiding in the early ripening of mangoes.
Advancing Monsoon (The Rainy Season)
- South-east trade winds originating over warm subtropical areas of the southern oceans cross the equator and enter India as the southwest monsoon.
- The monsoon winds cover the country for about a month, bringing heavy rainfall.
- Mawsynram in the Khasi Hills receives the highest average rainfall globally.
- The monsoon is characterized by breaks in rainfall, related to the movement of the monsoon trough and the frequency and intensity of tropical depressions.
Retreating/Post Monsoons (The Transition Season)
- October to November marks the transition from the rainy season to dry winter conditions.
- The retreat of the monsoon is marked by clear skies and rising temperatures.
- Days are hot, while nights are cool and pleasant.
- High temperatures and humidity during the day can make the weather oppressive, known as the “October heat.”
- Towards the end of October, temperatures start to drop rapidly in northern India.
Distribution of Rainfall
Parts of the western coast and northeastern India receive over about 400 cm of rainfall annually due to their proximity to the sea and the influence of the southwest monsoon winds. However, regions like western Rajasthan, parts of Gujarat, Haryana, Punjab, and the interior of the Deccan plateau receive less than 60 cm of rainfall. Similarly, areas east of the Sahyadris also experience low precipitation.
The low rainfall in these regions can be attributed to several factors:
- Distance from the sea: These regions are far from the coast, limiting the moisture-laden winds’ reach, resulting in reduced rainfall.
- Rain shadow effect: The Western Ghats act as a barrier, causing the moisture-laden winds to release most of their moisture on the windward side, leaving the leeward side (areas east of the Sahyadris) dry.
- Topography: Regions like western Rajasthan and parts of Gujarat are characterized by arid or semi-arid landscapes, where the topography does not support significant rainfall.
Areas around Leh in Jammu and Kashmir also experience low precipitation due to their high altitude and geographical features.
Annual rainfall in these regions is highly variable from year to year due to the nature of monsoons. Variability is particularly high in regions with low rainfall, making them susceptible to droughts. Conversely, areas with high rainfall are prone to floods due to excessive precipitation.
Monsoon as a Unifying Bond
The monsoon plays a unifying role across the Indian subcontinent, bringing a rhythmic cycle of seasons through seasonal changes in wind patterns and weather conditions. Despite the uncertainties and uneven distribution of rainfall, the arrival of the monsoon is eagerly awaited by people across India, from north to south and east to west.
These monsoon winds are important for agricultural activities, providing much-needed water and binding the entire country together in their significance.
Related Links
Chapter 4: Climate- FAQs
What is the significance of studying climate?
Understanding climate helps us comprehend the long-term patterns of weather in a particular region, influencing various aspects of life such as agriculture, economy, and culture.
What factors influence the climate of a place?
Several factors influence climate, including latitude, altitude, distance from the sea, wind systems, ocean currents, and relief features.
How does latitude affect climate?
Latitude determines the amount of solar energy a place receives. Generally, regions closer to the equator receive more sunlight and tend to have warmer climates, while those closer to the poles receive less sunlight and have colder climates.
Explain the impact of altitude on climate.
Altitude refers to the height of a place above sea level. As altitude increases, the temperature decreases. Therefore, higher altitude areas tend to have cooler climates compared to lower altitude areas.
How do wind systems influence climate?
Wind systems play a crucial role in distributing heat and moisture across the Earth’s surface. They can bring different weather conditions, such as rain or dryness, depending on their origin and direction.
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