The climate of India is difficult to generalize due to the country's large geographic size and varied topography. Many regions have their own microclimates (e.g. in mountain tops), and the mean climatic conditions in Kashmir (extreme north) are very different from those in the extreme south.
India's climate is strongly influenced by The Himalaya and the Thar Desert. The Himalaya ensure, by acting as a barrier to the cold north winds from Central Asia, that northern India is warm or mildly cool during winter and hot during summer. So, although the Tropic of Cancer (the dividing line between the tropical and sub-tropical regions) passes almost through the middle of India, India as a whole is considered to be a tropical country.
India has three distinct seasons:
Summer - from March to June
Rainy - from June to October
Winter - from November to March
Summer in northwestern India lasts from April to June, and in the rest of the country from March to June. The temperatures in the north rise as the vertical rays of the Sun reach the Tropic of Cancer. The hottest month for the western and southern regions of the country is April, while for the northern regions it is May. By May, most of interior India experiences mean temperatures over 32°C and maximum temperatures exceeding 40°C. Temperatures of 49°C and higher have been recorded in parts of India during this season. Near the coast the temperature hovers around 36°C, and the proximity of the sea increases the level of humidity. In southern India, the temperatures are higher on the east coast by a few degrees compared to the west coast.
Altitude affects the temperature to a large extent, with the higher parts of the Deccan plateau and hills being relatively cooler. The Himalayan and Nilgiri hill stations offer some respite from the heat with a temperate high of 25°C. Northeastern India also has a much milder climate with temperatures rarely exceeding 32°C.
The monsoons come as a relief from the heat and parched landscape. The rains bring down the temperature, and make the surroundings lush and green. It is the best season to go hiking and trekking. The monsoons are intricately linked to the economy as a good monsoon results in a booming economy. The rains fill the ground water tables and reinvigorate rivers and lakes.
The southwest monsoons supply over 80% of India's annual rainfall. There are two branches to the monsoon, the Bay of Bengal branch, and the Arabian Sea branch, extending to the low pressure area over the Thar desert in Rajasthan. The Arabian Sea branch is roughly three times stronger than the Bay of Bengal branch.
The monsoon makes its presence felt by the end of May. It starts around the 29 May, hitting the Andaman and Nicobar Islands in the Bay of Bengal. It strikes the mainland in Kerala by 1 June. By 9 June, it reaches Mumbai, and Delhi by 29 June. The Bay of Bengal monsoon moves in a northwest direction whereas the Arabian Sea monsoon moves north-northeast. By the first week of July, the entire country experiences rain. But usually southern India receives more rainfall than northern India.
During this season, cyclones occur, causing widespread devastation to coastal regions. Cherrapunji, Meghalaya, one of the world's wettest places, receives 2.65 meters of rainfall on average. The monsoons start withdrawing by the last week of August. By mid-September, they have withdrawn from Mumbai and by October, the southwest monsoons have completely withdrawn from India.
After the withdrawal of the monsoons, the northeast monsoons begin by November. Supplying 20% of India's rainfall, they don't cover the entire country but only the states of Tamil Nadu, West Bengal, Arunachal Pradesh, Karnataka and Meghalaya. Cold mountain air travelling along the Brahmaputra river brings rain to the northeast region of India.
The temperature gradually falls in the country after September. As the vertical rays of the sun move south of the equator, the country experiences cool weather, with temperatures decreasing by about 0.5°C for every 1° latitude moved north. December and January are typically the coldest months with mean temperatures of 10 to 15°C in the north-west and the Himalayan region. The mean temperatures increase as one moves east and south, where it can be between 20 to 25°C.
In northwestern India, October and November are cloudless and the least dusty months in the year, with feeble winds. This leads to a high diurnal range of temperatures during these months. It ranges between 16 to 20°C in north-western India, while it is nearly 5°C lower in central India and 10°C lower on the coastal strip. Northern India doesn't receive snow, except for the mountains and the temperature in the plains rarely falls below freezing. Highs in Delhi range between 12° to 18°C. Night time temperatures fall to between 2 to 6°C. Further north in the Punjabregion the low does fall below freezing in the plains: to around -6°C in Amritsar. Frost sometimes occurs, but the hallmark of the season is the notorious fog which disrupts daily life.
Northern India does receive some rainfall. The source is from the western disturbances originating in the Mediterranean Sea. As these disturbances travel eastwards, unable to "climb" the Himalaya they drop their rain and snow over northern India.
Eastern India has a much milder climate. It has mild days and cool nights. Highs range from 17- 21°C. Nights average 9°C. The northeast rainfall brings rain to this region. The cold winds over the Brahmaputra River lower the temperatures.
Tamil Nadu - Lake view of KodaikanalIn southern India, the weather is cooler only in the central part of the Indian plateau, the Karnataka plateau and hilly areas. This only lasts for a short period of time. These interior areas can fall to about 16°C. Coastal areas and low-level interior tracts are warm with highs of 30°C and lows of 21°C. The Nilgiri range is the exception, where the lows can fall below freezing.
Withdrawal of Monsoons
This is not a true season as such. Many text books however, refer to this as a separate season. This season lasts between September and December depending on its location. The weather turns more dry and the grass starts to dry up. This season marks the transition from wet to dry climate in most parts of India. Highs range between 34°C and 28°C.
Autumn and Spring
Autumn and spring seasons only occur in the Himalayan states of Himachal Pradesh, Kashmir and Sikkim. These regions have a temperate season and experience 5 seasons annually.
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