Factors Influencing Climate of India

The factors influencing the climate of India are: (i) Location and Latitudinal Extent, (ii) Distance from the Sea, (iii) Northern Mountain Ranges, (iv) Physiography, (v) Monsoon Winds, (vi) Upper Air Circulation, (vii) Western Disturbances and Tropical Cyclones, (viii) El - Nino Effect, (ix) Southern Oscillation

1. 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. Hence they experience low temperatures particularly, in winter. Water bodies surrounding peninsular India make climatic conditions mild along the coastal areas.

2. Distance from the Sea

Southern or 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. Contrary to this, the climate of the regions located in the interior of the country are cut off from the oceanic influence. As a result, they have an extreme or continental type of climate.

3. 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.

Further more, they act as an effective physical barrier for the rain bearing southwest monsoons winds to cross the northern frontiers of India. Thus, these ranges act as a climatic divide between Indian Sub-Continent and Central Asia.

4. Physiography

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

Bay of Bengal branch of Southwest monsoon is bifurcated into two parts - one moving along the Ganga Valley to the west and the other along the Brahmaputra Valley to the east.

5. Monsoon Winds

The complete reversal in the direction of winds over India brings about a sudden change in seasons - the harsh summer season suddenly giving way to the eagerly awaited monsoon or rainy season. These winds which change their direction completely are called monsoon winds.

The word ‘monsoon’ is derived from the Arabic word ‘Mousim’ 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.

(a) The Northeast Monsoon and its Effect

During winter, the weather conditions is influenced by high pressure developed over Northwestern part of the subcontinent. This results in the blowing of cold dry winds from this regions towards southern low pressure areas lying over water bodies surrounding 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 North-east Trades. In India they are essentially land bearing winds.

(b) 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 northwestern India but also on water bodies surrounding the peninsular.

As a result, North-east 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.

6. Upper Air Circulation

The changes in the upper air circulation over Indian landmass is another cause for sudden outbreak of monsoons in India. Jet streams in the upper air system influence the climate of India in the following ways:

(a) 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 sub-tropical 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 sub-continent. Winter rain and hail storms in northwestern 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.

(b) Easterly Jet 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.

7. 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. This rain is considered to be very good for wheat crops in northern plains.

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 October, November and December.

8. El - Nino Effect

Weather conditions in India are also influenced by EI-Nino which causes wide spread floods and droughts in tropical regions of the world. 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.

9. 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.