Climate of India

Introduction

We drink more water during summer and do not drink the same amount of water during winter. Why do we wear cotton or lighter clothes during summer season and heavy woollen clothes during cold weather season in north India? Why do not we wear woollen clothes in south India? This is because of the prevalence of varying weather conditions between north and south India.

Equable climate is also called as the British climate, Which is neither too hot nor too cold.

 

The factors affecting the climate

Climate of India is affected by the factors of latitude, altitude, distance from the seas, monsoon wind, relief features and jet stream.

Latitude

Latitudinally, India lies between 8°4'N and 37°6'N latitudes. The Tropic of cancer divides the country into two equal halves. The area located to the south of Tropic of cancer experiences high temperature and no severe cold season throughout the year whereas, the areas to the north of this parallel enjoys sub-tropical climate. 

Altitude

When the altitude increases, The temperature decreases. Temperature decreases at the rate of 6.50C for every 1000 metres of ascent. It is called normal lapse rate.

Hence, places in the mountains are cooler than the places on the plains. Ooty and several other hill stations of south India and of the Himalayan ranges like Mussourie, Shimla etc., are much cooler than the places located on the Great Plains.

Find out the temperature of Ooty (2240m) when it is 350C in Chennai (6.7m)

Distance from the Sea

A large area of India, especially the peninsular region, is not very far from the sea and this entire area has a clear maritime influence on climate. 

This part of the country does not have a very clearly marked winter and the temperature is equable almost throughout the year. Areas of central and north India experience much seasonal variation in temperature due to the absence of influence of seas. 

Here, summers are hot and winters are cold. The annual temperature at Kochin does not exceed 30°C as its location is on the coast while it is as high as 40°C at Delhi, since it is located in the interior part. Air near the coast has more moisture and greater potential to produce precipitation. 

Due to this fact, the amount of rainfall at Kolkata located near the coast is 119 cm and it decreases to just 24 cm at Bikaner which is located in the interior part.

Monsoon Wind

The most dominant factor which affects the climate of India is the monsoon winds. These are seasonal reversal winds and India remains in the influence of these winds for a considerable part of a year. 

Though, the sun’s rays are vertical over the central part of India during the mid-June, the summer season ends in India by the end of May. It is because the onset of southwest monsoon brings down the temperature of the entire India and causes moderate to heavy rainfall in many parts of the country. 

Similarly, the climate of southeast India is also influenced by northeast monsoon.

Weather refers to the state of atmosphere of a place at a given point of time. Climate is the accumulation of daily and seasonal weather events of a given location over a period of 30-35 years.

Relief

Relief of India has a great bearing on major elements of climate such as temperature, atmospheric pressure, direction of winds and the amount of rainfall. 

The Himalayas acts as a barrier to the freezing cold wind blows from central Asia and keep the Indian subcontinent warm. As such the north India experiences tropical climate even during winter. 

During southwest monsoon, areas on the western slope of the Western Ghats receive heavy rainfall. On the contrary, vast areas of Maharashtra, Karnataka, Telangana, Andhra Pradesh and Tamil nadu lie in rain shadow or leeward side of the Western Ghats receive very little rainfall. 

During this season, Mangalore, located on the coast gets the rainfall of about 280 cm whereas the Bengaluru located on the leeward side receives only about 50 cm rainfall.

Jet Streams 

Jet streams are the fast moving winds blowing in a narrow zone in the upper atmosphere. According to the Jet stream theory, the onset of southwest monsoon is driven by the shift of the sub tropical westerly jet from the plains of India towards the Tibetan plateau. 

The easterly jet streams cause tropical depressions both during southwest monsoon and retreating monsoon.

Monsoon and Four distinct seasons in India

Monsoon

The word ‘monsoon’ has been derived from the Arabic word ‘Mausim’ which means ‘season’. Originally, the word ‘monsoon’ was used by Arab navigators several centuries ago, to describe a system of seasonal reversal of winds along the shores of the Indian Ocean, especially over the Arabian Sea. 

It blows from the south-west to north-east during summer and from the north-east to south-west during winter.

Meteorologists have developed a number of concepts about the origin of monsoons. According to the Dynamic concept, Monsoon wind originates due to the seasonal migration of planetary winds and pressure belts following the position of the sun. 

During summer solstice, the sun’s rays fall vertically over the Tropic of cancer. Therefore, all the pressure and wind belts of the globe shift northwards. At this time, Inter -Tropical Convergence Zone (ITCZ) also moves northward, and a major part of Indian landmass comes under the influence of southeast trade winds. 

While crossing equator this wind gets deflected and takes the direction of southwest and becomes south-west monsoon. During the winter season, the pressure and wind belts shift southward, thereby establishing the north-east monsoon (trade winds) over this region. Such systematic change in the direction of planetary winds is known as monsoon.

Seasons

The meteorologists recognize the four distinct seasons in India. They are;

1. Winter season (January - February).

2. Summer season (March - May).

3. Southwest monsoon or Rainy season (June - September).

4. Northeast monsoon season (October - December).

1. Winter season

During this period, the vertical rays of the sun falls over tropic of capricorn which is far away from India. Hence, India receives the slanting sun’s rays which results in low temperature. 

The cold weather season is characterized by clear skies, fine weather, light northerly winds, low humidity and large day time variations of temperature. 

During this season a high pressure develops over north India and a north-westerly wind blows down the Indus and Ganges valleys. In south India, the general direction of wind is from east to west.

The rain during this season generally occurs over the Western Himalayas, Tamil nadu and Kerala. Western disturbances and associated trough in westerlies are main rain bearing system in northern part of the country. 

The jet stream plays a dominant role in bringing these disturbances to India. Western disturbances cause rainfall in Punjab, Haryana and Himachal Pradesh, and snowfall in the hills of Jammu and Kashmir. This rainfall is very useful for the cultivation of winter wheat.

2. Summer season

During this season, the vertical rays of the sun falls over the peninsular India. Hence, there is a steady increase in temperature from south to north. 

It is practically hot and dry in the entire country in the initial part of this season. Weather over the land areas of the country is influenced by thunderstorms associated with rain and sometimes with hail mostly in the middle and later part.

During this season, temperature starts increasing all over the country and by April, the interior parts of south India record mean daily temperatures of 30°C–35°C. Central Indian land mass becomes hot with day-time maximum temperature reaching about 40°C at many locations.

Because of the atmospheric pressure conditions, the winds blow from southwest to northeast direction in Arabian Sea and Bay of Bengal. 

They bring pre monsoon showers to the west coast during the month of May. There are few thunder showers called “Mango Showers” which helps in quick ripening of mangoes along the coast of Kerala and Karnataka.

“Norwesters ” or “Kalbaisakhis” are the local storms with thunder that blow from north western part and rain lasting for short durations. 

It occurs over the eastern and north eastern parts over Bihar, West Bengal and Assam during April and May. They approach the stations from the northwesterly direction.

3. Southwest monsoon or Rainy Season

The southwest monsoon is the most significant feature of the Indian climate. The onset of the southwest monsoon takes place normally over the southern tip of the country by the first week of June, advances along the Konkan coast in early June and covers the whole country by 15th July. The monsoon is influenced by global phenomenon like ElNino.

Prior to the onset of the southwest monsoon, the temperature in north India reaches upto 46°C. The sudden approach of monsoon wind over south India with lightning and thunder is termed as the ‘break’ or ‘burst of monsoon’. 

The monsoon wind strikes against the southern tip of Indian land mass and gets divided into two branches. One branch starts from Arabian sea and the other from Bay of Bengal.

The Arabian sea branch of southwest monsoon gives heavy rainfall to the west coast of India as it is located in the windward side of the Western Ghats. 

The other part which advances towards north is obstructed by Himalayan Mountains and results in heavy rainfall in north. As Aravalli Mountain is located parallel to the wind direction, Rajasthan and western part do not get much rainfall from this branch.

The Bay of Bengal branch moves towards northeast India and Myanmar. This wind is trapped by a chain of mountains namely Garo, Khasi and Jaintia are mainly responsible for the heaviest rainfall caused at Mawsynram located in Meghalaya. 

Later on, this wind travel towards west which results in decrease in rainfall from east to west. Over all about 75% of Indian rainfall is received from this monsoon.

4. Northeast monsoon season

The southwest monsoon begins to retreat from north India by the end of September due to the southward shifting pressure belts. The southwest monsoon wind returns from Indian landmass and blows towards Bay of Bengal. 

The coriolis force deflects this wind and makes it to blow from northeast. Hence, it is known as Northeast monsoon or Post- monsoon season. The season is associated with the establishment of the north-easterly wind system over the Indian subcontinent. Andhra Pradesh, Tamil nadu, Kerala and south interior Karnataka receive good amount of rainfall accounting for 35% of their annual total. 

Many parts of Tamil nadu and some parts of Andhra Pradesh and Karnataka receive rainfall during this season due to the storms forming in the Bay of Bengal. Large scale losses to life and property occur due to heavy rainfall, strong winds and storm surge in the coastal regions. The day time temperatures start falling sharply all over the country.

Distribution of rainfall

The average annual rainfall of India is 118 cm. However, spatial distribution of rainfall in the country is highly uneven.

The Western coast, Assam, South Meghalaya, Tripura, Nagaland and Arunachal Pradesh are the heavy rainfall areas which get more than 200 cm rainfall. 

The whole of Rajasthan, Punjab, Haryana, Western and Southwestern parts of Uttar Pradesh, Western Madhya Pradesh, the entire Deccan Trap or Plateau region east of Western Ghats except for a narrow strip along Tamil nadu coast receive a low rainfall of less than 100 cm. 

The rest of the areas receive a rainfall ranging between 100 and 200 cm.

Conclusion:

India experiences a diverse climate due to various factors such as latitude, altitude, distance from the sea, monsoon winds, relief features, and jet streams. These factors together determine the distinct weather patterns in different regions of the country. The interplay of the southwest and northeast monsoons, the geographical features like the Himalayas and the Western Ghats, and the varying altitudes contribute to the different seasons India experiences. The monsoon winds, in particular, play a significant role in shaping the climate, affecting agricultural patterns and rainfall distribution. The country is characterized by four distinct seasons—winter, summer, southwest monsoon, and northeast monsoon—which vary in intensity depending on the region. Understanding these climatic elements is essential to comprehend the natural vegetation, agricultural practices, and overall environmental dynamics of India.

 

Frequently Asked Questions (FAQs):

 

1.     What is the normal lapse rate of temperature in India?

o    The normal lapse rate is 6.5°C for every 1000 meters of ascent.

 

2.     How does altitude affect the climate in India?

o    As altitude increases, temperature decreases at the rate of 6.5°C for every 1000 meters of ascent. Higher altitudes like hill stations in India are cooler than the plains.

 

3.     What is the role of the Himalayas in shaping India's climate?

o    The Himalayas act as a barrier, preventing the cold winds from Central Asia from entering India, thereby keeping northern India warmer during winters.

 

4.     Why does the western coast of India receive heavy rainfall during the southwest monsoon?

o    The southwest monsoon winds from the Arabian Sea bring heavy rainfall to the windward side of the Western Ghats, resulting in high rainfall in the western coast.

 

5.     What is the difference between weather and climate?

o    Weather refers to the atmospheric conditions at a particular place at a given time, while climate refers to the long-term average of weather conditions over a period of 30-35 years.

 

6.     How does the southwest monsoon affect agriculture in India?

o    The southwest monsoon brings moderate to heavy rainfall, which is essential for agriculture, especially for the cultivation of rice, sugarcane, and other crops.

 

7.     Why is there a difference in the rainfall between the eastern and western sides of the Western Ghats?

o    The western side receives heavy rainfall as it is exposed to the southwest monsoon winds, while the eastern side, being in the rain shadow region, receives less rainfall.

 

8.     Which regions of India are most affected by the northeast monsoon?

o    The northeast monsoon affects the southeastern parts of India, especially Tamil Nadu, Andhra Pradesh, Kerala, and south interior Karnataka, bringing significant rainfall.

 

9.     Why does the temperature in India vary from region to region?

o    Temperature variation is influenced by factors such as latitude, altitude, distance from the sea, and the presence of relief features like mountains and plateaus.

 

10.                        What causes the retreat of the southwest monsoon?

o    The retreat of the southwest monsoon is caused by the shift in pressure and wind belts as the sun moves southwards, resulting in the northeast monsoon winds.