10 Factors which influence the climate of India are 1. Location and Latitudinal Extent, 2. Distance from the Sea, 3. The Northern Mountain Ranges, 4. Physiography, 5. Monsoon Winds, 6. Upper Air Circulation, 7. Tropical Cyclones and Western Disturbances, 8. El-Nino Effect, 9. La Nina, 10. Southern Oscillation !
1. Location and Latitudinal Extent:
The mainland of India extends roughly from 8°N to 37°N and the Tropic of Cancer of passes through the middle of the country.
Areas south of the Tropic of Cancer are closer to the equator and experience high temperature throughout the year.
The northern parts on the other hand lie in the warm temperature zone. Hence they experience comparatively low temperatures. Some places record considerably low temperatures particularly in winter. Water bodies comprising the Arabian Sea and the Bay of Bengal surround the peninsular India and make climatic conditions mild along the coastal areas.
2. Distance from the Sea:
Areas near the coast have equable or mariline climate. On the contrary, interior locations are deprived of the moderating influence of the sea and experience extreme or continental climate. For example the annual range of temperature at Kochi does not exceed 3°C whereas it is as high at 20°C at Delhi. Similarly, the amount of annual rainfall at Kolkata is 119 cm which falls to a low of 24 cm at Bikaner.
3. The Northern Mountain Ranges:
As mentioned earlier, India is separated from the rest of Asia by the impenetrable wall of the Himalayan mountain ranges. These ranges protect India from the bitterly cold and dry winds of Central Asia during winter. Further, these mountain ranges act as an effective physical barrier for rain bearing south-west monsoon winds to cross the northern frontiers of India. Thus, the Himalayan mountain ranges act as a climatic divide between the Indian Sub-continent and Central Asia.
Physiography of India has a great bearing on major elements of climate such as temperature, atmospheric pressure, direction of winds and the amount of rainfall. In fact, physical map of India is very closely related to the climatic conditions of the country. Places located at higher altitude have cool climate even though they are located in the peninsular India, i.e., Ooty.
Several hill stations and the Himalayan ranges are much cooler than the places located in the Great Plain of North India. The greatest control of physiography in the peninsular India is seen in the distribution of rainfall. The south-west monsoon winds from the Arabian sea strike almost perpendicular at the Western Ghats and cause copious rainfall in the Western Coastal plain and the western slopes of the Western Ghats.
On the contrary, vast areas of Maharashtra, Karnataka, Andhra Pradesh and Tamil Nadu lie in rainishadow or leeword side of the Western Ghats and receive scanty rainfall. The physiographic control of the mighty Himalayas over the climate of the country goes without saying.
The monsoon winds from the Bay of Bengal are bifurcated into two branches by the physiographic features. One branch goes to the Brahmaputra valley through the Meghalaya plateau. Here the funnel shaped Cherrapunji valley forces the moisture laden monsoon winds to rise along the steep slope and make this area the wettest place in the world.
The other branch of monsoons from the Bay of Bengal enters the Ganga valley. Its northward-movement is obstructed by the Himalayan ranges and it advances westwards up the Ganga plain. Initially this branch causes heavy rainfall but the amount of rainfall decreases as the monsoons loose much of the moisture content while advancing westwards.
5. Monsoon Winds:
The most dominating factor of the Indian climate is the ‘monsoon winds’ as a result of which it is often called the monsoon climate. The complete reversal of the monsoon winds brings about a sudden change in the seasons—the harsh summer season suddenly giving way to eagerly awaited monsoon or rainy season.
The south-west summer monsoons from the Arabian Sea and the Bay of Bengal bring rainfall to the entire country. The north-eastern winter monsoon travel from land to sea and do not cause much rainfall except along the Caromandel coast after getting moisture from the Bay of Bengal.
6. Upper Air Circulation:
The changes in the upper air circulation over Indian landmass influence the climate of India to a great extent. Jet streams in the upper air system influence the Indian climate in the following ways:
(i) Westerly Jet Stream:
Westerly jet stream blows at a very high speed during winter 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° north latitude.
Meteorologists believe that this branch of jet stream exercises a significant influence on the winter weather conditions in India. This jet stream is responsible for bringing western disturbances from the Mediterranean region in to the Indian subcontinent. Winter rain and heat 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 the whole of northern plains.
(ii) Easterly Jet:
Reversal in upper air circulation takes place in summer due to the apparent shift of the sun’s vertical rays in the northern hemisphere. The westerly jet stream as replaced by the easterly jet stream which owes its origin to the heating of the Tibet plateau. This leads to the development of an easterly cold jet stream centered around 15°N latitude and blowing over peninsular India. This help in the sudden onset of the south-west monsoons.
7. Tropical Cyclones and Western Disturbances:
Tropical cyclones originate in the Bay of Bengal and Arabian Sea and the influence large parts of the peninsular India. Majority of the cyclones originate in the Bay of Bengal and influence the weather conditions during the south-west monsoon season. Some cyclones are born during the retreating monsoon season, i.e., in October and November and influence the weather conditions along the eastern coast of India.
The western disturbances originate over the Mediterranean sea and travel eastward under the influence of westerly jet stream. They influence the winter weather conditions over most of Northern plains and Western Himalayan region.
8. El-Nino Effect:
El-Nino is a narrow warm current which occasionally appears off the coast of Peru in December. It is a temporary replacement of the cold Peru Current which normally flows along the coast. This current is responsible for wide spread floods and droughts in the tropical regions of the world.
Sometimes it becomes more intense and 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. Meteorologists believe that the severe drought of 1987 in India was caused by El-Nino.
9. La Nina:
After an El-Nino, weather conditions return to normal. However, sometimes trade winds become so strong that they cause abnormal accumulation of cold water in the central and eastern Pacific region. This event is called La Nina, which in effect is the complete opposition of El Nino. A La Nina also marks an active hurricane season. But in India, the presence of La Nina portends exceptionally good news. It is the harbinger of heavy monsoon showers in India.
10. Southern Oscillation:
There is a strange linkage of meteorological changes often observed between the Indian and the Pacific Oceans. It has been noticed that whenever the surface level pressure is high over the Indian Ocean, there is low pressure over the Pacific Ocean and vice-versa.
This interrelation of high and low pressure over the Pacific and the Indian Ocean is called Southern Oscillation. When the winter pressure is high over the Pacific Ocean and low over the Indian Ocean, the south-west monsoons in India tend to be stronger. In the reverse case, the monsoons are most likely to be weaker.