Climate: In India, the climatic regions are many, right from the alpine and temperate in the Himalayan north where there is sustained winter snowfall in the elevated regions, to the tropical in the south. The Thar Desert and Himalayas influence the climate of India, strongly.
When atmosphere is in a temporary state, it is termed as weather. The condition of weather over a longer time period is termed as climate.
Changes in weather happen quickly, ranging right from a day or week. However changes in climate, imperceptivity are observed even after 50 to 100 years and more.
In India, climatic regional variations are distinct, distinguishable by the level of dryness or wetness, patterns of rainfall, the repeated pattern of seasons, temperature and winter.
Climate is influenced by a number of factors, in India. Some of the major factors include:
Distance from the sea
Distribution of water and land
The Himalayan Mountains
Summer, winter and monsoon are the 3 main seasons in India.
Circulation of wind over the Indian subcontinent encounters a total reversal during summer at both the upper as well as lower levels. The low pressure belt close to the surface of ITCZ – the Inter Tropical Convergence Zone, by mid July moves parallel to the Himalayas, northwards. Inflow of winds from various directions gets attracted to this low pressure zone, the ITCZ. As the sun moves northwards in March towards the Tropic of Cancer, the temperatures increase in northern regions of India, indicating the summer season during the months of April, May and June.
Hot and dry winds blow in the afternoon and many times continue till midnight, in the northwest, in the heart of the ITCZ. Summer ends with pre-monsoon showers also called mango showers, in the coastal regions of Karnataka and Kerala.
A high pressure develops in the north of the Himalayas during winter. This gives rise to air flow at low level towards the south of the mountain range, from the north. The westerly winds influence all of Central and Western Asia along the altitude of 9-13 km from west to east and blow parallel to the highlands of Tibet. The Tibetan highlands however function as a barricade in the path of the westerly winds thus bifurcating and dividing them into two. While one branch is placed to the north of the Plateau of Tibet, the other branch is positioned to the south of the Himalayas.
From the southern hemisphere, the maritime tropical air mass crosses the equator and with force flows in a southwesterly direction (the low pressure area). The southwest monsoon is the moist air current that brings in rainfall in India. In June, over the southern part of the peninsula, an easterly jet stream flows at the same time at a maximum speed of 90 km per hour.
The tropical depressions, which play an important role in determining monsoon rainfall distribution over India, get steered by the easterly jet stream into India. High rainfall is seen in the areas wherever tracks of these depressions occur.
After crossing the Equator, the southwest monsoon deflects towards India. The monsoon burst is caused by the easterly jet stream. By the beginning of June, the Kerala coast gets the first southwest monsoon, after which between the 10th and 13th June, it reaches Mumbai and Kolkata respectively, gradually engulfing the whole subcontinent.
The southwest monsoon branches out, causing rain in the eastern coast and western coast of India. By mid-November, the cold weather season sets in Northern India. However the cold weather season is not well-defined in the Peninsula region of India.
One of the most prominent monsoon systems across the world is the Indian monsoon, effects of which are seen in India and the surrounding water bodies. During the cooler months, the monsoon blows from the northeast and during the warmer months, it changes its direction and blows from the southwest. During the months of June and July, rainfall in huge amounts falls in the region.
Area near the Equator in India is unique. All through the year, frequent or dominant westerly winds flow at the surface. By the month of February, the surface easterlies are able to reach to latitudes close to 20° N only, but with a strong northerly component. After drawing back northwards, tremendous change is seen in the upper-air circulation. This is an indication of transition time from the end of one monsoon to the initiating of the next monsoon.
Towards the end of March, the Equator experiences high sun which then moves towards the north. Rain, the turbulent and rising clouds and atmospheric instability also move northwards. Air flow is still controlled by the westerly subtropical jet stream across northern parts of India. The north-easterlies are the surface winds.
Development Of The Indian Monsoon
Since the northern highlands protect India from any cold air incursion during April while the high-sun season moves northward, India becomes more vulnerable to quick heating. Areas above the Tibet Plateau, above southern Bay of Bengal and across trunks of different relatively dry peninsulas, all get together forming a huge heat source region. Above the southern Bay of Bengal, a relatively warm area is created. Release of condensation heat, probably causes this heat source which does not appear at a lower level. On the other hand a heat sink appears over the southern part of the Indian Ocean, as the emitting long-wavelength radiation cools the air that is relatively free of clouds. At the surface, monsoon winds blow to heat source, from the heat sink, resulting in the southwest monsoon over Sri Lanka, by the month of May.
Heat which is transmitted readily to the immediate air above is absorbed and radiated by Tibet’s dry surface, during May. In the upper troposphere above northern parts of India, a strong easterly flow is created at around 6000 meters. Suddenly, the course is changed by the subtropical jet stream, which moves to the highlands and anticylclonic ridge in the north. Above northern India, the upper tropospheric circulation changes to easterly flow from westerly to coincide with a turnaround of pressure gradients and vertical temperature. Jet force is assumed by the easterly wind aloft, on many occasions. As the sun moves towards the north, the land gets heated due to the inverted triangular shape of India. The monsoon activity gets bigger over the Arabian Sea with the spread of heating in conjunction with the general direction of heat being transported by the winds. In the coastal regions, humidity increases relatively and causes some rain. On heated lands, the air below does not remain stable but the overriding easterly flow holds it down. However thunderstorms do occur in late May as well.
On reaching the Western Ghats in southern India, the southwest monsoon divides into 2 parts, with one moving up the coastal side of the Western Ghats and over the Arabian Sea, northwards. The other part through Assam flows over the Bay of Bengal and hits the Himalayan range in the East.
3.Indian Monsoons and the Tibet Plateau
The Indian monsoons do influence the Tibetan Plateau to quite an extent. Research by the IMD – India Meteorological Department indicates that around 130 years ago that a not so good monsoon was indicated by the snow cover in the Himalayas, during the preceding winter. From 1882, forecasts of the first monsoon were issued by IMD, on this basis. However prediction of the monsoon was not done very easily. Even today, it continues to remain a problem.
After some years later, the view established was that the monsoon was affected by the Himalayas in two ways. One view was that, during summer the Tibetan Plateau heated up due to which the atmospheric circulation established a condition suitable for the monsoon. As per the other view, the huge ranges of mountains acted as a tall blockade, preventing the warm winds filled with moisture from oceans that drive the monsoon and also dry cold air from making an entry into the Indian subcontinent. Other arguments from researchers state that one important factor was the role played by the Himalayas, as barrier for the monsoon.
Studies also indicate that the Himalayas and the adjacent mountain ranges would obstruct the entry of northern air, even in the absence of the Tibetan Plateau, and in the process not affect the monsoon.
Another study indicates that during the early and late parts of the monsoon season, there is correlation between the monsoon rainfall and heating of the Tibetan Plateau. During the summer months, the huge Tibetan plateau warmed up, heating the air above, to create a low pressure area above. In the process, the low pressure belt absorbed moisture from the oceans, thus causing the monsoon.
When the monsoon was setting in, correlation between the Tibetan plateau heating and rainfall from May 20 to June 15 over India was identified. However the correlation faded away but the rainfall appeared between September 1 and October 15 again when the monsoon became lesser.
In a study it was found that that surface waters of the tropical Pacific Ocean, underwent temperature swings near the El Nino-Southern Oscillation (ENSO), the international dateline due to which rainfall over the west coast and central India was influenced during the late and early stages of the monsoon.
Both factors, when taken together that is the ENSO and heating of the Tibetan plateau, acting independently of each other, could have predictive value for rainfall during the late and early phases of the monsoon. It appeared that during the entire season, both phases of the monsoon were responsible for more than one third of the rainfall in total.
4.Jet Stream and Indian Monsoons
One theory accepted by meteorologists from all over the world, with respect to origin of the monsoons, is the Jet Stream Theory. The basic mechanism of weather conditions induced by Jet Stream needs to be learnt to understand how Indian monsoons are affected by Jet Streams.
The Effect On Weather By Jet Streams
· The troughs and ridges or peaks, which Jet Streams have, are distinct.
· When warm air mass pushes against cold air mass, ridges occur.
· When cold air mass falls into warm air, troughs occur.
· Area on earth below ridge is at high pressure and is at low pressure, below the trough.
· The jet stream weakens due to lesser temperature contrasts between the temperate region and sub-tropics, thus causing this condition.
· Cyclonic condition is created by the trough region at the earth’s surface, while an anti-cyclonic condition is created by the ridge regions.
· Upper level divergence is created by troughs associated with low pressure cyclonic conditions. Upper level convergence is created by ridges, associated with high pressure in cyclonic conditions.
· Jet streaks result due to the troughs and ridges which are accountable for anti-cyclonic and cyclonic conditions at the surface of the earth.
· The jet streaks diverge rapidly due to the winds and in the process create a low pressure in the atmosphere’s upper level. The upper winds that flow out are replaced rapidly by the air below. Surface winds in the surrounding areas rush inwards creating a low pressure condition in the surface area. A cyclonic rotation is created by the Coriolis effect which is associated with low pressure cells.
· Due to atmosphere’s high pressure at the upper level, the winds rapidly converge while entering the jet streak. A divergence at the surface results due to the convergence at the upper troposphere.
· A clear, weather associated anti-cyclonic rotation, is created by the Coriolis effect.
A significant role is played by the Sub-Tropical Jet stream (STJ – a narrow band of fast moving air flowing to the east from the west) in a rapid onset of monsoons as well as obstructing the monsoon winds. The monsoon burst depends up on the STJ dominated upper air circulation. In the case of seasonal migration of STJ, in winter it flows along the southern Himalayan slopes and then in a dramatic manner shifts northwards. In late summer it flows along the Tibetan Plateau’s northern edge and in early June it flows along the northern edge of the Himalayas. The Jet Stream’s periodic movement is many times an indication of the coming and subsequent withdrawal of the monsoons. First onset of monsoon over India is indicated when the subtropical jet moves northwards.
In winter the sub tropical jet streams blows over the sub-tropical area, in very high speeds. The Tibetan Plateau and the Himalayan ranges, bifurcates the jet stream and unite again off the east coast of China. While the jet stream’s southern branch blows to the south of the Himalayan range and the northern branch blows along the Tibetan Plateau’s northern edge. The southerly jet develops, with differences in temperature along with other factors.
5.El-Nino and the Indian Monsoon
It is well known fact, all over the world that that surface sea temperatures influenced by the El Nino southern oscillation. It is understood that an irregular warm globe average surface temperature is caused by El Nino conditions. On the basis of temperature anomalies of peak sea surface temperatures, El Nino events of distinct types are possible. For many, one concern is forecast of not so good rainfall during the monsoon.
In every 3 to 7 years cycle, a nation experiences El Nino Southern Oscillation. This kind of a situation is experienced when the atmosphere and the Pacific Ocean’s warm water, interact. Various kinds of weather events, like droughts to floods across the world are caused by this interaction. During the 17th century, the El Nino (meaning the Christ Child or the Little Boy in Spanish) was recognized in South America’s coastal areas, first by fishermen.
Impact of El Nino on Monsoon in India
Various regions in South East Asia and Australia are influenced by the monsoon in India. Economy of not only India but countries in South East Asia gets impacted. While monsoon is forecast over India, it is expected that the relationship between the monsoon rainfall in India and El Nino is useful.
Monsoons in India and El Nino are generally related inversely. During the Southwest Monsoon, the trade winds that come from South America blow in the westward direction towards Asia. These winds become weak with warming of the Pacific Ocean. Hence, content of heat and moisture gets limited, resulting in unequal and reduction in rainfall distribution across India.
Are droughts in India caused by El Nino
Since the year 1871, in India there have been 6 prominent droughts triggered by El Nino. However it must be noted that not every El Nino year causes droughts in India. The El Nino was strong in the year 1997-98 but it didn’t cause drought in the nation. In fact rainfall was in abundance during that period. In the year 2002 there was a moderate El Nino, on the other hand caused one of the worst droughts in India.
Rainfall caused by around 90% of the El Nino years has been below normal as per data from the year 1880 to 2014, ranging for 135 years and around 65% of the advancing El Nino years have caused droughts. In terms of monsoon rain, this is an indication that weather in India is affected adversely by the El Nino years, with just a very few exceptions. Rainfall is below normal average generally during an El Nino year which affects production of crops, negatively.
6.Burst of Monsoon
The Burst of Monsoon is associated with the advent of the south-westerly humid winds, which override the dry and hot pre-monsoon routine which marks changes in conditions of weather in both south-east Asia and Indian sub-continent. There is correlation between the establishment of the inception of the high level easterly jet stream and changes in wind pattern.
Since more than 110 years, India has experienced annual average precipitation of 899 millimeters. The Indian subcontinent however experiences variation in the monsoons with a range of ±20%. Major floods result when the rainfall goes beyond 10 percent. Drought is significant, when there is rain shortfall is 10 percent.
Among the different global monsoons distributed geographically, South Asia’s monsoon is one significant monsoon. In India the monsoons are one of the most anticipated and oldest phenomena of weather. From June, right up to September it is a pattern that is economically important. However the Indian monsoon has not been understood fully and predicting it is extremely tough. To explain the strength, general vagaries, origin, distribution, process and variability of the monsoon, a number of theories have been presented. However extent of predictability of the monsoon and understanding them still continues.
Behavior of the monsoon is influenced greatly by unique geophysical, oceanic and atmospheric factors apart from the geographical features of the Indian subcontinent. The Indian monsoon is the most studied, monitored and anticipated weather phenomena in Asia, because of the effect it has on climates of countries like Sri Lanka, India, Pakistan, Nepal, Pakistan, Bhutan and Bangladesh as well as on flora and fauna and agriculture besides other environmental, social and economic effects. The burst of monsoon in India is also known as the ‘real finance minister of India’. Effect of the monsoon on overall well being of the people of the nation, is indeed significant.
When the monsoonal rainfall arrives in a sudden start, it is termed as the ‘Burst of monsoons’. In India when the monsoons arrive, there is sudden increase in the regular rainfall which continues to fall in a constant manner, for days together. In other words, the mean daily rainfall rises abruptly. An unanticipated increase in rains is the main characteristic of ‘Burst of monsoons’. It is during the first week of June that this monsoon burst can be experienced. During this southwest monsoon, the dry and hot weather, typically changes to humid and wet weather.
7.Breaks in the Monsoon
A break in the monsoonal rainfall is termed as break of monsoons. It is typically in the month of August, that the break of monsoons happens. Rainfall decreases sharply in most parts of India as the monsoon trough shifts to the north closer to the foothills of the Himalayas, during this period.
In the southwest monsoon period, after it rains for a few days, it may not rain for a period of 7 days or more, which is called a break in the monsoon. A common feature during the rainy season is such dry spells.
There are intervals, during the monsoon season, when the Monsoon channel moves towards the Himalayan foothills. Due to this, the rainfall decreases sharply over many parts of India.
However rain is abundant in Northeast India, the Himalayan foothills and in Tamil Nadu and Rayalseema (Southern Peninsula). This kind of situation is called the ‘break’ Monsoon period.
The ‘break’ Monsoon period has some striking features
In normal conditions the monsoon channel runs to Kolkata, from Sri Ganganagar in Rajasthan. However, in the ‘break’ monsoon the channel moves closer to the Himalayan foothills and at times it is not even visible.
The month most prone to ‘break’ monsoon is middle of August. The breaks are very long. Good showers are received by various parts in the south and northeast parts of India while remaining parts of the nation remains dry mainly.
Most regions of India do not get rainfall. Near and over foothills of the Himalayas, the monsoon showers are very heavy. Simultaneously it does not shower over the entire length of the nation.
Monsoon showers are heavy in the Himalayan range to the east of 85%E. Accordingly rainfall is heavier in regions like the Sub Himalayan West Bengal, Arunachal Pradesh, Assam and Sikkim. During this period, West Bengal, Bihar and Jharkhand receive more rainfall than normal. Thundershowers are good in Rayalseema, Peninsular India and Tamil Nadu.
Low level humidity is seen in the northern plains, there is considerable reduction in rainfall and surface winds begin blowing from the northwest. Due to temperature drop, the monsoon trough slopes normally towards the south with height. The trough does not indicate any southward slope, since monsoon in India takes a break.
Over Peninsula India, the pressure gradient weakens at surface levels. However over the Gangetic Plains, the pressure gradient becomes more. During the 4 month long monsoon season, normally, the opposite happens.
8.Seasons in India
The Indian continent, in South Asia, is surrounded on the east by the Bay of Bengal, the Indian Ocean on the south and the Arabian Sea on the west. Precipitation amount is huge in India. The amount of precipitation is huge allowing lush green vegetation in most parts of the country, especially the East.
As per the Indian calendar, spring, a period of lush flowering, begins around 20th March. The weather is hot and dry in wider regions of India. Temperatures vary from 27-30 degrees daily during this time. The festival of colors, a kind of spring festival called Holi, is celebrated in the month of March. Bhang, a drink made from the juice of hemp leaves and milk is consumed and people throw colors on each other and celebrate this festival.
March, April and May are the summer months in India after which begin the monsoon season. Heat is over 35 degrees during summer. The summer season is high in humidity levels and creates comfortable conditions for insect reproduction. The maximum and minimum average heat is around +39 degrees Celsius and +28 degrees Celsius.
The rainy season is from June to September in India. Generally it starts from the second week of June and lasts up to the 2nd week of October. Humid monsoon makes an entry in the south west direction from the Bay of Bengal from the second week of June, into different parts of India. The state experiences heavy rainfall in this season. As compared to the states in southern India, the northern states get less rain.
The season of storms is the autumn season or post monsoon season in India lasting from October to November. The rainy season is over, but as the cyclone comes in from the Bay of Bengal, rainfall and violent storms are generally observed. In the north east monsoon season, Tamil Nadu gets most of its annual precipitation.
Weather during this season is generally cloudless, comfortable, skies are clear, and weather is warm but not very hot. In these warm and pleasant days of the year, a range of festivals like the Ganesh Chaturthi (celebration of the birth of the diety, Ganesha), Onam (the harvest festival), Diwali (the festival of lights signifying victory over darkness) are celebrated in India.
December to February is the winter season in India. Ski resorts are opened for winter sports lovers in the Himalayas, at this time of the year. Rays of the sun fall obliquely on various parts of India as the sun is just over the Tropic of Capricorn, due to which there is decrease in temperature. During the months of January and February, the temperature is at its lowest. The dry North-East monsoon clouds pass over different regions of India. Temperature is very low ranging between 5 degrees and 10 degrees Celsius in the Himalayan area. However at times the cyclone arriving from the West can cause rainfall and storms, called as the Western disturbance.
A tropical cyclone is a rapid round and round movement or an area with intense low pressure, over the sub-tropical or tropical waters. The movement is more like a thunderstorm activity, in an organized convection, with a low level wind movement either clock-wise (in the southern hemisphere) or anti-clockwise (in the northern hemisphere. Strength of winds and intensity of cyclones depends upon pressure drop rate in the centre and the rate at which it increases outwards. Low pressure systems in the Arabian Sea and the Bay of Bengal are classified by India Meteorological Department, into 7 classes, as per criteria adopted by the W.M.O. (World Meteorological Organization). Tropical depressions are areas with low pressure and with maximum sustained surface winds having a speed ranging from 31 and 61 kp.h.
A tropical cyclone is caused when winds around the low pressure area reach, at a minimum of at-least 62 kp.h. The cyclone is termed as SCS (Severe Cyclonic Storm) when the wind speed is between 89 and 118 kp.h.
When the wind speed is between 119 and 221 kp.h, it is termed as a Very Severe Cyclonic Storm. It is called a Super Cyclone Storm when speed of wind increases to more than 221 kp.h. Low pressure systems have affected the Kerala coast up to the category of severe cyclonic storm.
Formation Of Cyclones
Particular conditions should exist for tropical cyclones to form.
Winds from the surface of the ocean blow from various directions converge and cause air to rise and form storm clouds.
A moist and warm air source from tropical oceans with temperature on sea surface, around 27 degree Celsius or excess.
At times low wind shear (winds that do not vary greatly with height) allow the storm clouds to rise at high levels, in a vertical direction.
Rotation of the earth induces spin (also called the Coriolis force). This mechanism formation differs across the globe. When the storm clouds cluster rotates, a tropical depression is formed which can turn out to become a tropical storm or a super cyclone if the rotation continues.
Storms could last for 7 days or more besides which one cyclone or more can occur at the same time in the same region. Forecasters provide tropical cyclones with names for easier description.
It was World War II that the names were provided to tropical cyclones and all regions adopted the practice subsequently. Names were used for all tropical storms by the mid 1960s excluding those in the North Indian Ocean. Responsibility of naming the tropical storms is taken up by different meteorological organizations. Tropical cyclones occurring in the Indian Seas are alphabetically arranged according to the name of the nation that gave the cyclone its name. Only when a tropical storm reaches a particular strength, it is named.
A thunderstorm is an intense and small weather system that makes strong thunder, lightning, heavy rain and winds. A thunderstorm can occur depending upon two situations, namely when there is no stability in the atmosphere and when air near the surface of the earth is moist and warm with lots of liquid. Each second, the earth is hit by 100 lightning bolts. At any given point of time, the earth can be hit by around 1800 thunderstorms.
In the winter season, thunderstorms are rare due to cold climatic conditions. A Thundersnow is a situation when thunderstorms occur in blizzards in the winter season. Generally, as compared to the early morning time, the clouds are more during the afternoon. The reason for this is that, by afternoon, the ground warms up and the winds blow upwards. Once the air goes up high enough, the water vapor present in it undergoes condensation and forms a cloud, depending upon the humidity and temperature levels and the height, at which this happens. Unless and until a lot of moisture is added (which helps the updraft) the puffy clouds do not change. Heat increases due to the moisture as the cloud warms up in the inside and moves up at a greater speed only to form a tall cumulus cloud. Within the cloud, the winds are so strong that it causes lightning and thunder at a height of 25000 feet. By this time the inside of the cloud is very cold and forms ice crystals. Once the cumulus cloud hits the warm stratosphere, it stops growing. At times, certain thunderstorms could grow twice the height of Mount Everest.
The top of the clouds get smoothened and spread out, due to strong winds in the stratosphere, giving them the appearance of a mushroom top. It gets a fuzzy look due to ice crystals in the cloud. As the thunderstorm starts growing, ice crystals present inside the cloud become bigger in the process of hitting and mixing with each other. The cloud’s bottom area becomes darker, with water drops getting heavier, till they fall from the cloud in the form of hail or rain. The falling water drops mix up with smaller water drops while falling and turn into bigger drops. Inside the cloud, the hail gets larger and by 30-50 minutes there is not much energy left in the thunderstorm. Supercell thunderstorms can continue for hours till the outflow dissipates them.
Out of all thunderstorms, just about ten percent are considered to be severe, causing high winds at a speed of miles per hour, with others being tornadoes and flashfloods.
Thunderstorms are considered dangerous however they can be a great blessing to all living creatures and man. They act like natural air conditioners. Hot air on the surface of the earth rises high up into the atmosphere and is put into its space. During summer, continents get water in abundance and plants get the much needed rain for survival. Pollutants present in the air are washed away by thunderstorms.
In the Indian economy, one element that is most important is rainfall. Many parts of India experience rainfall, with variations from scanty to very heavy in different regions. As far rainfall distribution is concerned, there is tremendous temporal and regional variation. June to September is the 4 month period when the monsoon arrives which provides more than 80 percent of the annual rainfall. Approximately 125 cm. is the average rainfall that falls in India. However, the spatial variations are indeed great.
Regions receiving more than 200 cm of heavy rainfall are the Southern slopes of eastern Himalayas, Assam, West Coast of India and Assam.
Regions receiving moderate rainfall up to 50-100 cm are Tamil Nadu, Upper Ganga valley, Andhra Pradesh, Eastern Rajasthan, Southern Plateau of Karnataka and Punjab.
Regions receiving moderately heavy rainfall upto 100-200 cm. are Madhya Pradesh, the middle Ganga Valley, Western Ghats, Orissa and Eastern Maharashtra.
Regions receiving scanty rainfall that is less than 50 cm. are Western Rajasthan, the Deccan Plateau, Punjab and the Northern part of Kashmir.
Rainfall in India has 2 significant features namely that rainfall decreases westwards in the northern parts of India and decreases eastwards in Peninsular India, excluding Tamil Nadu.
A co-efficient variation formula is used for expressing variability of rainfall. Large variation in the actual amount of rain from year to year is calculated by the Coefficient of Variation as follows:
(C) =Standard Deviation / Mean x 100
Changes from the mean values of rainfall are shown by the values of coefficient of variation. In India 20% to 50% is the coefficient of yearly rainfall. In south western parts of Jammu and Kashmir, north eastern India, Himachal Pradesh, the north eastern peninsula, the western coasts, Uttarakhand, eastern plains of the Ganga and the Western Ghats, the variability exits upto less than 25 percent.
In the northern parts of Rajasthan, interior parts of the Deccan Plateau and the western parts of Rajasthan, the variability of rainfall is more that 50%. The yearly rainfall in these regions is less than 50 cm. Variability of 25% to 50% exists in remaining parts of India. Rainfall variability is lower when the rainfall is higher.
Since many centuries, the rainiest place on earth has been Cherrapunji (the Land of Rain) located around 56 kms from Shillong the capital of Meghalaya. It is situated between Jaintia, Gharo and Khasi hills at a height of 4500 feet above Mean Seal Level (MSL). Topsoil in this region is not very good and has large reserves of limestone and coal beneath. Hence though there is rainfall here all year through and the topsoil is wet, water is not available in wells in this area.
12.Variability of Rainfall
In India, in terms of time and space, the variability of rainfall is very unpredictable at multiple scales. Based on the Köppen classification system the climatic zones in India include:
a.The tropical rainy climate group
b.Dry climate group
c.Sub-tropical humid climate group
India is vast in terms of size due to which there are large climatic variations from one region to the other. It is from 4 major climatic groups that climate is experienced by India which are divided further into 7 climatic types.
The Tropical Rainy Climate Group
Continuous high temperature is experienced by regions falling in this group. In any given month, the temperatures hardly go below 18 degree Celsius.
Tropical Rainforest Climate
This kind of climate is experienced in the Western Coastal Plains, the Andaman-Nicobar & Lakshadweep islands, the Western Ghats including the state of Goa, Konkan region of Western Maharashtra, West Bengal, the Kanyakumari and Nilgiris districts of Tamil Nadu, South Gujarat, entire Kerala State, Karnataka’s coastal/western Kanara region and all eight states of north east India.
All through the year, these regions and mountains experience high temperatures along with both frequent and heavy rainfall daily, above 300 cm a year. Rains from April to October are enough for vegetation growth all through the year. 60mm is the average precipitation due to which there is no dry season during the year. A typical feature of the region is the tropical wet forests, a result of heavy rain here.
Tropical Wet Climate
Excluding the semi-arid tract to the east of the Western Ghats, a tropical wet climate is enjoyed by most of the plateau of Indian peninsula. Temperature is above 18 degree Celsius in the winter season and early summer. It is hot during summer and during May, temperatures can go above 45 degree Celsius in the interior low level areas. June to September is the rainy season and 75 and 150 cm is the annual rainfall. Central eastern Tamil Nadu falling under this tract gets rains during November to January, the winter months.
Dry Climate Group
Regions falling in this group experience higher water evaporation rate as compared to moisture received through precipitation.
Tropical Semi Arid Climate
To the east of the Western Ghats on its Leeward side and south of Tropic of Cancer is a long stretch of land that experiences a tropical semi arid climate. As the region is located in the rain-shadow area, it receives minimal rainfall. Rainfall is not reliable ranging from 40 and 75 cm annually, so this zone is more prone to famines. The summer monsoon is responsible for most of the rain towards north of the Krishna River. During the months of October and November, rainfall occurs to the south of the river. Even in December which is the coldest month, the temperature varies from 20 to 24 degree Celsius. Temperature is around 32 degree Celsius in the hot and dry months of March to May. Due to rainfall there are a few scattered trees and grasses due to which permanent agriculture is not suitable.
Sub Tropical Arid Climate
The Kutch Region of the Western Ghats, North Gujarat and the entire Thar Desert Region fall under the sub tropical arid climate category. Rain is scanty here. The only rainfall is caused by cloud bursts provided with just less than 30 cm rainfall. In the months of July, August and September, the monsoon winds penetrate this region causing erratic rainfall with some regions not getting rain for some years even. Climate is extreme with very cold winters and very hot summers making it a region in India with sparse population.
Sub Tropical Semi Arid Climate
This climate is experienced by regions Kathiawar regions of Gujarat, Central Gujarat, Delhi, Western Uttar Pradesh to Malwa and Gird regions in Western Madhya Pradesh, Haryana, Southern Punjab and eastern fringes of Rajasthan. During the summer monsoon season, unreliable rain falls between 30 and 65 cm in this region annually. Climate here is less extreme, with minimum temperatures dropping to freezing point and maximum rising to 45 degree Celsius. Except the monsoon season, not much humidity is experienced by regions through the year, falling under this belt.
Sub Tropical Humid With Dry Winters
This type of climate is experienced in the Punjab-Haryana plain, Himalayan foothills, Bihar, Assam, Rajasthan east of the Aravalli range and northern part of West Bengal. It rains in summer up to 65 cm in the west and increase near the Himalayas to 250 cm annually. Summers are hot with temperature rising to 46 degree Celsius in the lowlands and winters are mainly dry. Natural vegetation differs widely due to difference in rainfall in these regions.
For every 100 m rise in altitude, the temperature falls by 0.6 degree C, in the Himalayan Mountains. Depending upon altitude sharp contrast is seen in temperatures here. Rains are scanty in the northern side of western Himalayas leading to sparse vegetation. It rains heavily of the exposed slopes and less rain falls on the Leeward side of the Himalayas. Rainfall is at its heaviest at places located between 1070 and 2290 m altitudes. Above 2290 m there is rapid decrease in rain.
13.Climatic Regions of India
Climate of India can be described broadly as tropical monsoon type. The 4 official seasons designated by the IMD – The Indian Meteorological Department are 1.Winter (December to early April) 2. Summer (April to July in north-western India) 3. Rainy Season (June to September) and 4.Post-monsoon season (October to December. However, traditionally 2 more seasons (in the ancient Hindu calendar) that is spring and late autumn and winter of 2 months each are also included.
There are 2 seasonal winds in the climate of India namely:
The south-west monsoon (summer monsoon) which crosses the Bay of Bengal, the Arabian Sea and the Indian Ocean and blows from sea to land and the north-east monsoon (winter monsoon) which blows from land to sea. India receives most of the monsoon from the south-west monsoon.
What Affects The Climate Of India
The climate of India is affected by a number of factors. Special characteristics of the climate are defined by tropical location that is presence of the Indian Ocean and Himalayas indicating that it is tropical monsoon type in a broader sense. Tropical climate is experienced in areas south of Tropic of Cancer. Warm temperate climate is experienced by regions to the north of the Tropic of Cancer.
Climatic pattern is impacted by the large size of India. Maritime climate is experienced by areas near the sea while continental climate is experienced by areas away from the sea.
With changes in season, the circulation of seasonal wind reverses thus affecting the monsoon.
The Himalayan Range in the north proves to be a physical barrier for the South-West monsoon that bears rain.
Entire India gets rain from the South-West summer monsoon from the Bay of Bengal and the Arabian Sea. Also the North-East winter monsoon travels to sea from land, gets moisture from the Bay of Bengal and provides rain along the Coromandal coast.
The jet streams influence the climate and monsoon in India. High pressure centers get intensified over the North-Western India in the winter season by the south branch of the jet stream. Onset of the South-West monsoon is seen due to easterly jet stream of the summer season.
As compared to the Bay of Bengal, the Arabian monsoon branch is more powerful. It is in the Andaman and Nicobar Island that the onset of monsoon takes place and then in the Kerala Coast.
Rainfall distribution is affected by periodic movement of jet streams, the tropical cyclones that generate in the Bay of Bengal and Arabian Sea, influence of winter weather conditions by Western disturbances and the El Nino which reverses the ocean surface’s thermal condition.
Rainfall in India is classified into 4 broad categories:
Regions with very high rainfall with areas getting rainfall upto 200 cm and above, are the western coast from Thiruvananthapuram to Mumbai as well as North-East India.
Regions getting 100-200 cm high rainfall include East coasts, major parts of Northern Plain and Eastern slopes of Western Ghats.
Regions getting 50-100 cm low rainfall include Eastern Rajasthan, major part of Gujarat etc.
Regions getting below 50 cm, very low rainfall include Kutch, the arid and semi arid areas of Western Rajasthan and many parts of Ladakh, Jammu and Kashmir.
Agriculture in India is mainly dependent on the monsoon rainfall. In fact the entire economy of India revolves around the monsoon.
14.Koppen’s Classification of Indian Climate
Many climates across the world are classified by the Köppen Climate Classification System. Classification of climates as per this system is based on the monthly and annual averages of precipitation and temperature. Five types of major climates are recognized by the Köppen system. A capital letter has been used to designate each climate type.
A.Tropical Moist Climate
The average temperature is above 18 degree Celsius during all the months in tropical moist climates and the annual precipitation is more than 1500 mm. This climate extends southward and northward from the equator approximately to about 15 to 25 degree latitude. In this group there are 3 minor types of Köppen climate and depending on their seasonal rainfall distribution, their designation is based. Variations in monthly temperature are less than 3 degree Celsius. Almost each day, cumulonimbus and cumulus clouds are formed due to high humidity and intense heating of the surface. While average temperature is 22 degree Celsius at night time, it is approximately 32 degree Celsius during the day. It rains very less during the dry season. During winter, the dry season extends during the tropical wet and dry or savanna. Precipitation is less than 1000 mm generally during the wet season and only during the hot season.
Precipitation is less than normal all the year round in dry climate regions. One climatic feature of this climate that is most obvious is that the potential transpiration and evaporation is more than the precipitation. This climate types extends North and South of the equator to about 20-35 degrees and often mountains surround the large continental regions of mid-latitudes.
This climate includes minor types of climate namely:
Dry arid climate
Desert or dry arid climate is a true climate of the deserts. Xerophytes vegetation dominates around 12 percent of land surface on the earth. H and K are letters used additionally to distinguish if the dry arid climate is found in the mid-latitudes or subtropics Mediterranean respectively.
Dry semiarid, grassland or the steppe climate
This climate covers around 14 percent of the land surface on Earth. The mid-latitude or the inter-tropical convergence zone cyclones provide it with more precipitation. The letters H and K are used for distinguishing in general whether the dry semiarid climate is prevalent in the mid-latitudes or the subtropics Mediterranean, respectively.
C.Moist Subtropical Mid-Latitude Climates
Winters are mild and summers are humid and warm generally, in a moist subtropical mid-latitude climate which extends mainly on the western and eastern borders of many continents, from 30 to 50 degree latitude. The mid-latitude cyclone is the main weather feature in winter time. Summer months are dominated by convective thunderstorms. The 3 minor types of moist subtropical mid-latitude climates are humid, subtropical, Mediterranean and marine.
D.Moist Continental Mid-latitude Climates
Winters are cold and summers are warm to cool, in moist mid-latitude climate regions. The Pole ward of the C climates is the location of these climates. In the coldest month, the average temperature is less than -3 degree Celsius and greater than 10 degree Celsius in the warmest month. Bitter cold from the Arctic or Continental Polar air masses, the strong winds and snowstorms make winters more severe. There are 3 minor type climates like other climates including wet all seasons, dry summers and dry winters.
All through the year winters and summers are extremely cold in Polar Climate regions. Temperature is less than 10 degree Celsius in the warmest month. Polar climates prevail in Europe, northern coastal regions of North America, landmasses of Antarctica and Greenland and Asia. Polar Tundra and Polar ice cap are the two types of minor climates that exist. The surface is covered permanently with ice and snow in a polar ice cap climate. In a condition called permafrost, the soil is frozen permanently upto hundreds of meters deep in the case of a Polar Tundra climate. Mosses, scattered woody shrubs, dwarf trees and lichens dominate the vegetation.
15.Climatic Divisions by Stamp and Kendrew
India is divided into 2 major climatic divisions by Stamp and Kendrew, on the basis of the 18 degree isotherm (which follows the Tropic of Cancer almost).
Rainfall and temperature are the bases used in the Stamp and Kendrew classification. India is divided into Tropical and Continental regions by the 18 degree Celsius winter isotherm. The sub-divisions made further are made according to the rainfall amount.
Subtropical or Continental India
The 2 major climatic regions are divided further, into 11 regions as given below:
1.Subtropical or Continental India
The Himalayan region (which gets heavy rainfall)
This region extends to the northern and north eastern parts of India. The determinant and decisive factor for the amount and cause of rainfall is altitude. The mean winter temperature ranges from 4°-7°C and mean summer temperature ranges between13-18°C.
Rainfall reduces towards the west ranging from 125 cm in the west, 150 cm in the middle and more than 200 cm in the east. During winter, it snows.
b.The North-Western Plateau (which gets moderate rainfall)
Mean temperature during summer is 34 degree Celsius, to the northwest of Sutlej while the mean winter temperature remains 16 degree Celsius. Average rainfall caused by winter cyclones is just about 40 cm.
c.The North West arid low lands (dry plains)
Rajasthan, Punjab and South West Haryana are the North West arid low lands. In winter the mean temperature is 13-24°C and in summer it is 46°C. The average rainfall is less than 50 cm annually.
d.The region of moderate rainfall
Eastern Rajasthan, Western UP, Delhi, Haryana and Punjab are regions that get moderate rains. In winter the mean temperate is 15°-18°C and in summer it is 35°C. The high annual rainfall is 40-80 cm. In summers it is partially dry, however winter cyclones cause rain in winters.
e) Transitional Zone
Easter Uttar Pradesh and Northern Bihar fall in the Transitional Zone. In winter the mean temperature is 16-18°C and summer it is 35°C. Rainfalls up to 100-150 cm is caused by the South West Monsoons.
a.Regions with very heavy rainfall
Rainfall is very high in the middle lower Ganga Valley. Mean temperature during winter is 18-24°C and in summer it is 29-35°C. Mean rainfall is 100-200 cm less towards southwards and the west.
Regions with heavy rainfall
All the North-Eastern States have humid climate and get heavy rainfall. The rainy season is long. Annual rainfall on an average is over 250 cm.
c.Regions with moderate rainfall
Western Andhra Pradesh, Gujarat, Karnataka and areas between eastern and western Ghats get moderate rainfall. Due to rain shadow effect the annual rainfall at an average is 75 cm. Mean temperature in winter is 18-24°C and 32°C in summer.
d.Tamil Nadu Coast
The annual temperature range is 3°C. Rainfall to the extent of 100-150 cm is caused by the retreating monsoons.
Rainfall is heavy in the Goa-Kanyakumari. Rain exceeds to more than 500 cm annually. The south west monsoons bring rainfall. Annual temperature range is around 3°C (low).
Right from the Narmada Estuary to Goa the day-night temperature range is 3°C (very less). The average rainfall is caused by the south west monsoon to more than 200 cm.
16.Trewartha’s Classification of Indian Climate
Classifications of climatic regions in India are most satisfactory as per Dr.Trewartha’s scheme. Koppen’s classification in a modified form has been presented by him. The 4 major regions India is divided as per classification by Dr. Trewartha is A, B, C and H types.
The A climate type is the tropical rainy climate in which there is consistency in high temperatures.
The B climate type refers to dry climate where temperatures are high and rainfall is little.
The C climate type refers to a climate where winters are dry and temperature is low ranging between 0 °C and 18°C.
The H climate type refers to mountain climate.
Climates A, B and C are sub-divided further. There are 7 types of climates.
1.Tropical Rain Forest (Am)
In this climate type, temperatures are high and even in winters temperatures do not fall below 18.2°C Such a climate is found in parts of Assam, Sahyadris and West Coastal plains. In the hottest months, April and May, the temperatures increase to 29°C. During May-November, the annual rainfall, which is seasonal in nature, is around 200 cm.
2.Tropical Savanna (Aw)
In this climate type, temperatures go high, up to 46 to 48 degree C. This climate type exists in the peninsular areas regions excluding the semi-arid zone in the windward side of the Western Ghats. In winters the mean temperature comes to above 18.2 degrees C and in summer to about 32 degrees C.
It rains from the month of June to September and it may continue up to the end of December in the South. Variations are seen in the annual rainfall in the east and west. During October to December, much more rainfall and equitable temperature is experienced in Tamil Nadu. This climate type is a class tied under the Tamil Nadu Aw sub-type.
3.Tropical Semi-Arid Steppe Climate (BS) TI
This climate type belt runs from central Maharashtra southwards to the leeside of the Western Ghats that is Tamil Nadu, interior of Tamil Nadu, Karnataka state, the Cardamom Hills and western Andhra Pradesh. Variations are seen in temperature in December from 20 to 23.8 degree Celsius and in May 32.8 degree Celsius which are the coldest and hottest months respectively. Variations in annual rainfall are from 40 to 75 m and hence it is known as the tl1 famine zone of India.
4.Tropical and Sub-Tropical Steppe (BSh)
This climate exists from Punjab, Kutch, through the Thar Desert and over western Rajasthan and northern Gujarat. In January temperature varies from 12 degree C to 35 degree C in June. The coldest and hottest months of the year are January and June. Temperature rises to a maximum of 49 degree C and the erratic rainfall varies from 30.5 to 63.5 annually.
5.Tropical Desert (BWh)
This climate exists in the western parts of Bikaner, Jaisalmer and Barmer districts of Rajasthan and Kutch. During the hottest months in May and June, the month temperature is 34.5 degree C high. Temperature decreases during winters towards the north. Annual rainfall is scanty upto 30.5 cm. Some parts get low and erratic rainfall upto 12.7 cm.
6.Humid sub-tropical climate with dry winters (Caw)
Large area to the east of the sub-tropical and tropical steppe, eastern part of the Aravalli range in Rajasthan, the south of Himalayas and north of the tropical savanna from Punjab to Assam is covered with this climate type. In the western part, summers are very hot, they are mild in the east and winters are mild to severe. The hottest months are May and June. During the south west monsoon season, variation in annual rainfall seen is from 63.5 cm to 254 cm. Towards the north and east, the atmosphere is humid and it rains more. Westerly depressions bring little rain and winters are dry.
7.Mountain Climate (H)
Mountainous regions rising above 6000 m and above including the Himalayas experience this climate. Between temperatures of shady and sunny slopes, a sharp contrast is seen. Rainfall variability and temperature inversion is seen while ascending higher altitudes from more than 1500 m.
Rainfall is scanty, climate is cold and dry and vegetation is stunted and sparse, in the northern side of the western Himalayas (The Trans-Himalayan belt). The annual and daily temperature range is high in this area. The south-west monsoons bring heavy rainfall at a height of 1069 to 2286 m above sea level, on the slopes of the Himalayas which are otherwise protected from the northerly cold winds.
17.Climatic Divisions of India by R.L. Singh (1971)
In 1971, Dr. R. L. Singh, after following Kendrew and Stamp, presented the climatic divisions of India. On the basis of annual rainfall and temperature conditions of the coldest and hottest months, he divided India into ten climatic divisions.
As indicated by the name, the humid North-East covers many parts of the north-eastern states, including Nagaland, Meghalaya, Sikkim, Mizoram, Assam, Tripura and Arunachal Pradesh. Temperature in the month of July ranges from 25 to 33 degree Celsius, which in January falls to 11 to 24 degree C. At many place, the average annual rainfall is 200 cm. However the rainfall record is 1000 cm at some places.
2.Humid West Coast And Sahyadri
The western coast belt including the Western Ghats (Sahyadris) extending from the north from the Narmada Valley to the south in Kanyakumari is included in this climatic division. In January the temperature is 19-29 degree C which in July, rises to 26-32 degree C. It rains about 200 cm at an average annually but on the western slopes of the Western Ghats, rainfall is higher.
This climatic division includes Jharkhand, Orissa, Chhattisgarh and West Bengal. Temperatures are 12-27 degree C and 26-34 degree C in July and January respectively. Annual rainfall at an average is 100-200 cm.
This climatic division cuddles the northern part of Jharkhand and eastern part of Uttar Pradesh. Temperature in the month of January is between 9-24 degree C and in July it rises from 24 to 41 degree C. Annual rainfall is 100 to 200 cm at an average.
This type of climate prevails in coastal Andhra Pradesh and Eastern Tamil Nadu. Temperature rises to 28 to 38 degree C in the hottest month in May. Temperature falls to 20-29 degrees in January. Winters are wet and summers are dry. Annual rainfall received by the whole area is 75-150 cm. In November-December, retreating monsoon, cause this annual rainfall.
This climate prevails in the Ganga Plain, primarily. Temperatures are 7-23 degree C and 26-41 degree C in January and July respectively. Variation in average annual rainfall is 75 to 150 cm.
Semi Arid And Subtropical
This climate type is seen the Satluj-Yamuna water divide including Haryana, Chandigarh, Punjab, Union Territories of Delhi, Haryana and eastern Rajasthan. Western disturbances in winter cause some rains from 25 to 100 cm. Temperatures are 6-23 degree C, in January which in May month increases to 26 to 41 degree C.
Semi Arid Tropical
Semi arid tropical climate is seen in Andhra Pradesh, Madhya Pradesh, Gujarat, Karnataka, Maharashtra and Chhattisgarh. In January the temperature varies from 13-29 degree C and in July from 26-42 degree C. Variations in annual rainfall are 50-100 cm at an average.
This extremely dry climate is present in Kutch region of Gujarat, Thar Desert, southwest Haryana and western Rajasthan. It rains annually to about 25 cm at is as little as 10 cm at some places. The temperature in January is 5-22 degree C which in June rises to 20-40 degree C. Very large variations are seen in both diurnal and annual temperature range.
This type of climate region is found in the west Himalayan region, including Uttaranchal, Jammu and Kashmir and Himachal Pradesh. Temperature in July is 5-30 degree C in July which falls down to 0-4 degree C in January. It rains up to 150 cm annually. Western disturbances cause rain in winter and in summer it is the south west monsoons.
Over the eighteenth and nineteenth centuries, the worst droughts in the world have occurred in India, causing deaths in millions, due to famine in the country. Rajasthan, Maharashtra, Gujarat, Karnataka, Orissa, Andhra Pradesh and some parts of Haryana, Punjab, Jharkhand and Bihar are some of the most affected states and in the process the winter season rice crop has been affected by drought.
Rajasthan – Jaisalmer and Bikaner
Jaisalmer and Bikaner, both fall in the drought prone regions of Rajasthan. Other places affected by drought are Nagaur, Barmer and Jodhpur.
Maharashtra – Jalna Beed
Severe scarcity of water is faced by the Marathwada region of Maharashtra. Hingoli, Jalna, Aurangabad, Osmanabad, Nanded, Parbhani, Latur and Beed are 8 districts affected by drought with Jalna being the most affected.
Gujarat – Saurashtra
Kutch is a region in Saurashtra district that is not only one of the hottest places in India, but is also known as dead land due to lack of water.
Karnataka – Chitradurga and Bijapur
Chitradurga district located in northern Karnataka is worst hit by drought. Other areas most affected by drought include Hubli, Bijapur, Bagalkot and Dharwad as well.
Orissa – Mayurbhanj-Balasore
Rainfall shortage made Orissa’s Mayurbhanj-Balasore region a drought prone area. In 1866, it became one of the worst drought hit area in history.
Andhra Pradesh – Mahbubnagar-Khammam
In the year 2002, Mahbubnagar-Khamman district in Andhra Pradesh was declared as drought hit as it was affected by delayed and poor monsoon.
Poor farmers suffer losses of crops and severe shortages of water due to drought at many places India. Weak monsoons affect millions of people in India time and again. After wells dry up, farmers and poor families have to walk long distances in search of water, when summer hits. Drinking water is rationed to people in an effort to tackle the crippling rainfall shortage. Efforts are put in by the government to provide relief to areas hardest hit by the droughts.
When temperature rises earlier than normal and summer reaches its height every year, hundreds of people especially the poor die in India due to drought. Meteorological department of India issues heat-wave warnings with forecast of high temperatures. In Orissa many schools remain closed for a few days because of the heat and water shortage.
Agriculture in India is mainly dependent on a favorable monsoon and on its climate. Shortage of water results in crop yields that are below average as well as shortage of water.
Studies indicate that severe drought has correlation with ENSO - El Niño-Southern Oscillation events. These events cause abnormally high temperatures on sea surfaces in the Indian Ocean, thus causing increased evaporation in the oceans and an unusually wet weather in parts of India. Such instances have occurred in 1997 and 1998. In the 1900s a warm spell began causing these types of anomalies. One phenomenon in contrast is that a low pressure convergence centre is formed by in the ocean that is ENSO related. Dry air from Central Asia (including India) is pulled continually, which otherwise should experience the humid summer monsoon season. Droughts in India are caused by the reversed air flow. The degree of drought is influenced by sea surface temperatures in Central Pacific Ocean, affected by the ENSO event.
When water is carried in enormous volume by creeks, rivers and various other geographical features into regions where adequate water drainage does not exist, then flooding occurs. Many times when rainfall is very heavy, but drainage systems are not sufficient enough or civil development remains unchecked, then the drainage system gets affected. Fatalities in huge numbers result, due to floods. Dams, lakes and rivers overflow due to excessive rain in India, which in turn causes damage to property and life. India has witnessed some of the most catastrophic and largest floods in history which have caused irreparable damage to property, livelihood of people as well as crucial infrastructure.
A number of states in India are affected by floods and landslides. Mizoram State has been affected by heavy rain, in the month of June 2018, causing casualties and landslides. The north eastern state of Assam also has been affected by the onset of monsoon with heavy rains causing floods and casualties in various districts. As per records of NERC – National Emergency Response Centre, the death toll has been high in Kerala, Manipur, West Bengal, Maharashtra and Tripura, due to heavy monsoon. The southern part of Kerala has been greatly affected by heavy spell of monsoons and downpours to an extent that in 8 districts, disaster alert has been declared by the authorities. With low-lying areas being inundated with flood waters, people have to seek refuge at relief camps. Worst affected in Kerala are districts of Ernakulam, Alappuzha and Kottayam. Other districts are also affected by with damage to property and crops and landslides.
People are reported to being hit by walls collapsing or die of drowning. During the monsoon when water level in rivers crosses the danger mark, people living on river banks are shifted on higher ground, to tents. Uttar Pradesh too has been affected in 2018 by lighting and rain related incidents.
South west monsoons over Kerala at times cause landslides and flooding by incessant rains over many days. Kerala is a state with forty four rivers. During heavy rainfall, excess water is released through dams, which in turn causes flooding in many of the districts.
Madhya Pradesh, Uttar Pradesh and Rajasthan also experience heavy rains and flood like situations during the monsoon season. Water overflows the reservoirs and dams, after which alert is issued in lower regions of the dams whose gates are opened.
One of the worst floods was in Madras in October 1943. Heavy rains lasted for 6 days causing floods, overflow of the Adyar and Coovum rivers and damage to property and life.
In Gujarat –Rajkot district, Morbi town was flooded on 11th August 1979 with an estimate of around 2500 people losing their lives.
Bihar saw one of the worst floods in 1987, when the Koshi riveir overflowed, claiming lives in thousands besides loss to animal life and public property.
Mumbai in Maharashtra experiences heavy rains time and again. On 26th July 2005 around 1094 people lost their lives besides an estimated property loss of about 550 crores, with Mumbai receiving 944 mm rains. The airport remained closed for 30 hours while Mumbai came to a standstill with the rains.