Objectives, Climatic Variations in India, Factors Influencing the Climate of India Part 1

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In the previous chapter, we have noted the shape and size of our country along with its latitudinal extent. Each one of these factors has an impact on climatic conditions of India, be it temperature, atmospheric pressure, wind system or precipitation. We will now study the regional variations in the climatic conditions of India and identify a series of factors responsible for these climatic variations both over space and time. We would study the basic concept of monsoons and their typical characteristics.

The major objectives of this chapter are:

  • To explain both seasonal and spatial climatic variations in India with suitable examples

  • To name various factors which influence the climate of different parts of India

  • To explain the concept of monsoon and its causes

  • To discuss the typical characteristics of monsoons

  • To state the climatic conditions during different seasons

Climatic Variations in India

The climatic conditions of southern India are a bit different from those of the northern parts with respect to temperature, rainfall, and commencement as well as duration of different seasons.

During the month of June, areas of Rajasthan desert record day temperatures around 55°C, while the temperatures around Gulmarg or Pahalgam in Kashmir are hardly around 20°C. Similarly, in the month of December, in Kargil or Dras in Jammu and Kashmir, the night temperatures drop to -40°C, while the inhabitants of Thiruvananthapuram experience temperatures around 27°C.

The range of temperature increases as one move away from coastal areas to interior parts of the country. As a result, the people living along Konkan and Malabar coasts do not experience extremes of temperatures or marked change in seasons. But people living in north western parts of India, experience sharp seasonal contrasts.

The diversity in rainfall distribution is equally striking. Mawsynram, near Cherrapunji in Meghalaya, receives about 1080 cm of rainfall annually, while Jaisalmer in the desert of Rajasthan receives only 20 cm of annual rainfall. The north-eastern parts and the coastal plains of Orissa and West Bengal experience spells of heavy rain during July and August while the Coromandel coast of Tamil Nadu receive very meagre rain during these months.

The dates of onset and withdrawal of southwest monsoons will help us to understand the difference in the duration of rainy season in different parts of India. The duration of rainy season is the shortest in northwest India and longest in the south and north-eastern parts of the country.

Normal dates of Onset of South - west Monsoons

Normal Dates of Onset of South - West Monsoons

Normal dates of Onset of South - west Monsoons

Factors Influencing the Climate of India

The factors influencing the climate of India are as follows:

Location and Latitudinal Extent: India lies roughly between 6°N to 37°N latitudes. The Tropic of Cancer passes through the middle of the country. The southern parts being closer to the Equator, experience high temperatures throughout the year. The northern parts on the other hand lie in the warm temperate zone that experience low temperatures particularly, in winter. Water bodies surrounding the peninsular India make climatic conditions mild along the coastal areas.

Distance from the Sea: The peninsular India is surrounded by the Arabian Sea, the Indian ocean and the Bay of Bengal, hence the climate of coastal regions of India is equable or maritime. On the other hand, the climate of the regions located in the interior of the country are cut off from the oceanic influence. Hence, they have an extreme or continental type of climate.

The Northern Mountain Ranges: The Himalayan and adjoining mountain ranges which extend from Kashmir in the northwest to Arunachal Pradesh in the northeast, separate India from the rest of Asia. These ranges protect India from the bitterly cold and dry winds of central Asia during winter. They act as an effective physical barrier for the rain bearing southwest monsoons winds to cross the northern frontiers of India.

  1. Physiography: The physical features influence the air temperature, atmospheric pressure, direction of winds and the amount of rainfall in different parts of the country. The western coastal plains receive more rainfall than the interior parts of Karnataka and Tamil Nadu lying east side of the Western Ghats.

  2. Monsoon Winds: The winds which change their direction completely are called monsoon winds. The word monsoon is derived from the Arabic word ‘mausim’ which means season. These winds have such a far-reaching influence on India’s climate that it is termed as monsoon type of climate. The nature of these winds can be described with reference to the surface distribution of pressure in different regions of India during winter and summer seasons.

    1. The Northeast Monsoon and Its Effect: During winter, the weather condition is influenced by high pressure developed over north-western part of the subcontinent. This results in the blowing of cold dry winds from this region towards southern low-pressure areas lying over water bodies surrounding the peninsular India. Since these winds are cold and dry, they do not cause rainfall and weather conditions under their influence remain cold and dry. However, wherever these northeast monsoon winds collect moisture while passing over the Bay of Bengal, they bring rain along Coromandel coast. These winds are planetary winds known as Northeast Trades. In India, they are essentially land bearing winds.

    2. The Southwest Monsoon and Its Effect: During summer, the north-western parts of India become very hot due to very high temperature. This is ascribed to the apparent shift of the sun in northern hemisphere. This results in the reversal of air pressure conditions not only in north-western India but also on water bodies surrounding the peninsular. As a result, northeast trade winds are replaced by southwest monsoon winds. Since these winds are sea bearing and blow over warm water bodies before reaching land, they are moisture laden, causing wide spread rain over the most parts of India. This period of southwest monsoon from June to September is known as the rainy season for most parts of the country.

  3. Upper Air Circulation: Jet streams in the upper air system influence the climate of India in the following ways:

    1. Westerly Jet Stream and Its Impact: During Winter, at about 8 km above sea level, a westerly jet stream blows at a very high speed over the subtropical zone. This jet stream is bifurcated by the Himalayan ranges. The northern branch of this jet stream blows along the northern edge of this barrier. The southern branch blows eastwards south of the Himalayan ranges along 25°N latitude. It is believed by meteorologists that this branch of jet stream exercises a significant influence on the winter weather conditions over India. This jet stream is responsible for bringing western disturbances from the Mediterranean region into Indian subcontinent. Winter rain and hail storms in north-western plains and occasional heavy snowfall in hilly regions are caused by these disturbances. These are generally followed by cold waves in whole of northern plains.

    2. Easterly Jet Stream and Its Influence: During summer, due to the apparent shift of the sun in northern hemisphere, the reversal in upper air circulation takes place. The westerly stream is replaced by easterly jet stream which owes its origin to the heating of the Tibetan plateau. This leads to the development of an easterly cold jet stream centered around 15°N latitude and blowing over peninsular India. This helps in the sudden onset of monsoons.

  4. Western Disturbances and Tropical Cyclones: The inflow of western disturbances moves under the influence of westerly jet streams from the Mediterranean Sea. It influences winter weather conditions over most parts of northern plains and western Himalayan region. It brings little rain in winter months.

    The tropical cyclones also develop in the Bay of Bengal. The frequency and direction of these cyclones influence weather conditions along the eastern coast during the months of October, November and December.

  5. El-Nino Effect: El-Nino is a narrow warm current which sometimes appears off the coast of Peru in South America. It is a temporary replacement of the cold Peru current which normally flows along this coast. Sometimes, becoming more intense, it increases the surface water temperatures of the sea by 10°C. This warming of tropical Pacific waters affects the global pattern of pressure and wind systems including the monsoon winds in the Indian Ocean. It is believed that the severest drought of 1987 over India was caused by EI-Nino.

  6. Southern Oscillation and its Effect: The southern oscillation is a pattern of meteorological changes which are often observed between Indian and Pacific Oceans. It has been noticed that whenever the surface level pressure is high over Indian ocean, it is low over Pacific Ocean and vice-versa. When the pressure is high over the Pacific Ocean and low over Indian Ocean, the southwest monsoons in India tend to be weaker. In the reverse case, the monsoons are most likely to be stronger.

EI - Nino, Walker Circulation and Southern Oscillation

EI - Nino, Walker Circulation and Southern Oscillation

EI - Nino, Walker Circulation and Southern Oscillation