CLIMATE OF INDIA
- In spite of the great diversity and variation in Indian climate and topography, the most important factor that lends unity to India is the fact of the monsoons.
- The word ‘Monsoon’ owes its origin to the Arabic word ‘Manusin’ Meaning ‘season’.
- The term was used by seamen several centuries ago, to describe the system of alternating winds over the Arabian Sea.
- These winds appear to blow from the southwest for six months and from the northeast for another six months.
- The winds which reverse their directions completely between the summer and the winter is known as Monsoon winds. Due to these monsoon winds, India Experiences a Tropical monsoon climate.
The salient features of Tropical Monsoon Climate
- The Monsoon winds are classified into Southwest Monsoon and Northeast Monsoon on the basis of the direction from where they below.
- They are caused due to the differential heating of land and sea.
- The main feature of monsoon winds is an alternation of seasons which determines the climate of India.
Season
- On the basis of the monsoon Variation, the meteorologists recognize the four distinct seasons in India such as
- Winter (December to February)
- Summer (March to May)
- Southwest Monsoon (June to September)
- North-East Monsoon (October to November)
Winter (December to February)
- During winter, the sun is overhead in the Tropic of Capricorn.
- The land Mass becomes cold in North India where the daily mean temperature remains below 21oC No obvious difference is found in the temperature during day and night.
- In the meantime, high pressure develops in the north-western part of India due to the prevalence of low temperature.
- In contrast to this, a low-pressure area forms in South India, that is both in the Arabian Sea and Bay of Bengal.
- Consequently the winds below from the high-pressure area of northwest India towards South India.
- These winds are called the ‘Retreating monsoon winds’ which blow from land to sea and do not cause much rainfall.
- These winds absorb some moisture while crossing the Bay of Bengal and gives winter rainfall to Tamil Nadu and South Andhra Pradesh.
- This is the main characteristics feature of Retreating monsoon.
- During this period, a low-pressure depression originates over the Mediterranean Sea and Travels eastwards across Iran and Pakistan and reaches India.
- This low-pressure depression is called ‘Western disturbance’.
- The jet stream plays a dominant role in bringing this disturbance to India.
- These disturbances cause rainfall in Punjab, Haryana and Himachal Pradesh which is very useful for the cultivation of wheat.
- It also brings snowfall in the hills of Jammu and Kashmir.
Summer (March to May)
- The summer season starts in March and continues up to May. During this season the Sun‘s rays are vertical over the Tropic of Cancer.
- Therefore the temperature is very high in the northern parts of India.
- At some places in northwest India, the day temperature may be as high as 450
- Due to this high temperature, low-pressure conditions prevail over the northern part of India.
- Because of the atmospheric pressure conditions, the winds blow from south-west to northeast direction in Arabian Sea and Bay of Bengal.
- They are a few thundershowers called ‘Mangoshowers’ which helps in quick ripening of mangoes along the coast of Kerala and Karnataka.
- The north-eastern part of India also experiences local storms called ‘Norwesters’. These thunderstorms are called as Kal Baisakhi (calamity of the month of Baisakh) in Punjab.
- Strong hot winds blow during day time over northern and northwest parts of India are called as ‘Loo winds’.
Southwest Monsoon (June to September)
- After the summer season, the rainy season starts with the onset of south-west monsoon.
- The high temperature gives rise to low pressure and by the end of May, a large area of low pressure is formed over the North West part of the country.
- At the same time, the oceans become cool and a high-Pressure area develops over the oceans. We know that wind always blows from high pressure to low pressure.
- Hence the winds blow from oceans towards the land of India. These winds blow from South-East directions.
- When they cross the equator, they get deflected and blow as South West Monsoon. These winds are moisture-laden winds because they originate from the Indian Ocean.
- When they approach the Southern part of Kerala they give rain with violent thunderstorms indicating the onset of the monsoon and lightning. This phenomenon is often termed as the ‘Monsoon burst’.
- The south-west Monsoon is normally divided into two branches because of the peninsular shape of the country.
- They are Arabian Sea branch and Bay of Bengal Branch.
Arabian Sea Branch
- The more powerful Arabian Sea branch of monsoon wind and brings heavier rainfall.
- Blowing from the Arabian Sea, the first part of the wind first strikes against the Western Ghats.
- This moisture-laden wind is forced to ascend the slopes, condenses and gives heavy rainfall to the western coastal region.
- Mumbai gets heavy rainfall of over 150 cms as it lies on the windward side of Western Ghats while Pune gets less than 50 cms of rainfall as it lies on the leeward side (rain shadow) of the Western Ghats.
- The second part of this wind blows through the Vindhya – Satpura ranges and strikes against the Rajmahal hills and cause heavy rainfall in the Chotanagpur Plateau region.
- The Third part of this wind moves towards Rajasthan where the Aravalli Mountains stand parallel to the direction of this wind.
- Hence it is not able to strike against the mountain and does not give any rain to Rajasthan
- This is the reason why a part of western Rajasthan remains to be a desert.
- This wind then reaches Himachal Pradesh and combines with the Bay of Bengal branch.
- It gets obstructed by the Shiwalik hills and gives a good rainfall to the foothills of this region.
Wind ward side
- The wind striking side of the mountain is called the windward side of a mountain, which receives heavy rainfall.
Rain Shadow region
- Rain Shadow region is an area receiving relatively less rainfall due to the obstruction of mountains.
Bay of Bengal Branch
- This branch of Monsoon, blowing from the Bay of Bengal is ‘Moisture bearing wind’.
- It strikes against the Khasi, Garo, and Jaintia hills.
- This moisture-laden wind takes a sudden rise over the funnel-shaped hills and causes heavy rainfall in Cherrapunji, which receives the highest rainfall in India.
- A part of this branch gets deflected by the Himalayas and moves towards the west giving rain to the Gangetic plains.
- As it moves further westwards, it loses its moisture content and gives scanty rainfall to Punjab and Haryana.
- Finally, this wind meets the Arabian Sea branch of monsoon wind at the foothills of the Himalayas and gives heavy rainfall along the Siwaliks.
- Tamil Nadu remains dry during this period because it lies in the rain shadow area, of the Arabian Sea branch monsoon and it lies parallel to the Bay of Bengal branch.
North-East Monsoon (October to November)
- The South West Monsoon begins to retreat from Northern India by the second week of September because of the apparent movement of the sun towards tropic of Capricorn.
- The landmass of India starts losing heat and there is a fall in the temperature. But the sea is still in warm condition.
- High pressure develops over the land and low pressure over the sea.
- Therefore wind blows from high pressure to low pressure that is from land to sea.
- It is cold dry wind and gives no rainfall to the landmass.
- When it crosses the Bay of Bengal, it absorbs moisture and gives heavy rain to the Coromandal coast.
- So Andhra Pradesh and Tamil Nadu get heavy rainfall during winter. There are frequent cyclones formed in the Bay of Bengal and they cause damage to life and property along the Coromandal coast.
FEATURES OF THE MONSOON
Uneven distribution of Rainfall during the year
- The South West Monsoon causes over 80 per cent of the rainfall over the country from June to September.
- The normal duration of the Monsoon varies from two to four months.
- Normally it – withdraws from the north-west by the beginning of September and from the remaining part of the country by the end of October and in some parts by November.
Influence of Mountains
- The rainfall is very much influenced by orographic features.
- Though the wind passes over Gujarat and Rajasthan, it brings very little rainfall due to the absence of mountains.
- Along the west coast, the winds strike the Western Ghats and bring heavy rainfall on the windward side.
- For example, the Shillong plateau receives heavy rainfall (annual rainfall at cherrapunji 1,270 cm) while the central part of the Assam Valley which is situated in the leeward side receives less rainfall (annual rainfall at Guwahati 163.7cm).
Tropical Cyclone
- The intensity and distribution of rainfall are determined by a series of tropical depressions (low-pressure systems) which have their origin near the northern part of Bay of Bengal and travel across the country in West and northwesterly direction.
- On an average eight, such cyclonic depressions may pass from the Bay of Bengal into the land area between June and September.
Cyclone
- A cyclone is a small but intense low – pressure system in the Arabian Sea or Bay of Bengal which produces violent winds and heavy rainfall.
Erratic nature of the Rainfall
- It is difficult to make any general statement describing the rainfall in any particular state.
- Because the same areas which received heavy rainfall in one season.
- Sometimes the beginning of the rain may be delayed.
- There may be breaks in the monsoon rain during July and August; sometimes the rain disappears for a week or more.
- The monsoon may also withdraw earlier than usual or may persist longer than usual.
Monsoon rains have a great effect on the country ‘s economy
- The prosperity of India depends on the success or failure of the Monsoon.
- Slight variations in the directions of rain-bearing winds may convert normally well-watered areas into deserts.
- For example
- Gujarat
- The Deccan plateau is particularly liable to drought.
- The Hydroelectric power plants are affected severely in times of low rainfall.
- The supply of electricity to industries is rationed resulting in great loss in Economy.
Rainfall during summer
- The annual rainfall varies from about 1187 cm to less than 25 cm.
- At Mawsynram, a station 16 km west of cherrapunji in the state of Meghalaya receives 1187 cm rainfall which is the highest in the world.
- Less than 25 cm of rainfall is found in the Thar Desert in Rajasthan.
- The erratic nature of Monsoon creates havoc at times due to unprecedented rainfall.
WINTER RAINFALL
- Winter rainfall which sets in over the Bay of Bengal in October and meets with the damp winds of the retreating summer monsoon.
- This current curves round over the Bay of Bengal and blows directly into the Tamil Nadu coast giving that region the wettest and most disturbed weather of the whole year (mainly during October and November).
- Heavy rains accompanied by stormy winds sweep over the coastal regions causing widespread damage to standing crops and disorganizing means of transport.
- Similarly, Nagapattinam receives an average of 100 cm out of its total rainfall of 140 cm in the cold season.
- The rainfall is higher along the coast than in the interior.
- It decreases rapidly on land so that over the Mysore plateau in Karnataka receives only about 3 or 4 cm.
Distribution of Rainfall
- The distribution of rainfall over the country as we have noted earlier is determined by two main factors.
These are
- The direction of the rain-bearing winds
- The position of the mountain ranges.
- Due to these factors about 30 percent of the area of our country receives from 15 to 80 cm, 40 per cent receives from 80 to 120 cm and about 10 percent receives over 200 cm.
On the basis of the amount of rainfall our country can be divided into four rainfall regions as follows
Region of Very Heavy Rainfall
- The area with over 200 cm of rain are the southern slopes of the Eastern Himalayas, Assam, Bengal and the west coast region comprising the Konkan and the Malabar Coast.
Region of Heavy Rainfall
- Areas with rainfall between 100 to 200 cm are the Middle Ganga Valley, Western Ghats, Eastern Maharashtra, Madhya Pradesh and Orissa.
Regions of Moderate Rainfall
- Areas with 50 to 100 cm of rainfall are the upper Ganga valley, Eastern Rajasthan and Punjab, Southern Deccan comprising the plateau regions of Karnataka, Andhra Pradesh and Tamil Nadu.
Regions of Scanty Rainfall
- The area with less than 50 cm is the northern part of Kashmir, western Rajasthan, southern Punjab and regions of the Deccan in the rain shadow of the Western Ghats
Water Management
- Water management implies making the best use of available water resources for human benefit, while not only controlling its depletion and degradation but also for our future needs.
- Water is an indispensable resource and has multiple uses.
- Therefore, it becomes extremely important to manage our soil and water resources in an integrated manner.
- Water management must be undertaken at all levels.
The basic requirements for water conservation activities are
- The total involvement, co-operation and participation of all local people
- The role of women in managing household water needs.
- The most important aspect of water management is to treat water resources an economic commodity to be used in a profitable and satisfying manner.
- In the distribution of this economic (commodity) good both equity and quality must be ensured.
- We can save the water through “rainwater harvesting” strategy.
Rainwater Harvesting
- India experiences a tropical monsoon type of climate. It gives seasonal rainfall. It is not uniform and is highly erratic.
- Most of the time the rainfall is scanty, hence it is necessary to save available rainwater.
- We must allow this water to penetrate into the deep water table and tap this water when it is needed.
- In order to prevent surface runoff, we must harvest the rainwater for future domestic-related and other activities.
- Hence Rain harvesting is an activity of direct collection and storage of water for our purpose or it can be recharged into the ground for withdrawal later.
- Through rain harvesting, we can understand the real value of rain and make optimum use of it.