The changes in weather conditions of India can be broadly categorised into four distinct patterns. These are the cold weather season, the hot weather season, the advancing monsoon and the retreating monsoon.
India has cold weather in the winter that begins in mid-November and lasts till February. The northern parts of India are the first to experience the cold. December and January are the coldest months in northern India. The southern parts of India do not experience very low temperatures.
Frost is a common phenomenon in the north plains, while the higher slopes of the Himalayas experience snowfall.
During winter, the north-east trade winds blow over the country. In most parts of India, the weather during the winter is dry. In some parts like the coast of Tamil Nadu, the winds blow from the sea to the land. Hence, these places receive some amount of rainfall during the winter.
Other characteristic feature of the winter season experienced over the northern plains is the inflow of cyclonic disturbances from the west and the north-west. The winter rainfall is locally known as “mahawat”.
The sea has a moderating influence over the peninsular region of India. Hence, there are no drastic seasonal variations in temperature pattern, and winters are not as distinct as in the north. The hot weather season in India refers to the summers that begin in March and lasts till mid-June.
In India, summer is caused due to the apparent northward movement of the sun, which shifts the global heat belt northward. ‘Loo’ are strong, gusty, hot, dry winds that blow during the day over north and north-western India.
In northern India, dust storms are also very common during the month of May. This is also the season for localised thunderstorms, associated with violent winds, torrential downpours, often accompanied by hail. Pre-monsoon showers are common, especially in Kerala and Karnataka and are often referred to as ‘mango showers,’ as they help in the early ripening of mangoes.
The advancing monsoon in India refers to the rainy season that lasts for a period of four months from June to September. The trade winds from the southern hemisphere, which originate over the warm subtropical areas of the southern oceans, bring the south-west monsoon winds into India.
Another characteristic feature of the monsoon is the ‘breaks’ in rainfall and refers to the alternating wet and dry spells of rains. The Indian monsoon is very unpredictable. These breaks occur due to the movement of the monsoon trough.
The farming schedule of millions of farmers all over the country, which is dependent on the monsoons, can sometimes get disturbed. The retreating monsoon refers to the transition season that lasts from October to December.
The months of October-November form a period of transition from the hot rainy season to dry winter conditions. The main cause of this transition is the movement of the sun towards the south. By the beginning of October, the monsoon withdraws from the Northern Plains. The retreating monsoon season is marked by clear skies and a rise in the temperatures. The land is still moist and the weather becomes hot and humid. The days can become quite oppressive. This is commonly known as ‘October heat’.
Due to the unpredictable nature of the monsoon, the distribution of rainfall varies drastically from region to region. Major variations can also be seen in the annual precipitation from year to year. The phenomenon of monsoon is an integral part of the Indian landscape, animal and plant life, agricultural calendar, and the life of the people and their festivities.