Climate of India and Factors Affecting it
India is home to an extraordinary variety of climatic regions, ranging from tropical in the south to temperate and alpine in the Himalayan north, where elevated regions receive sustained winter snowfall. India’s climate is strongly influenced by the Oceans, Himalayas and the Thar Desert. The Himalayas act as a barrier to the frigid katabatic winds flowing down from Central Asia keeping the bulk of the Indian subcontinent warmer than most locations at similar latitudes.
The climate of India may be broadly described as tropical monsoon type. India’s climate is affected by two seasonal winds viz. the north-east monsoon and the south-west monsoon.
- The north-east monsoon commonly known as winter monsoon blows from land to sea whereas south-west monsoon known as summer monsoon blows from sea to landafter crossing the Indian Ocean, the Arabian Sea and the Bay of Bengal.
- The south-west monsoon brings most of the rainfall during the year in the country.
As such, land areas in the north of the country have a continental climate with severe summer conditions that alternates with cold winters when temperatures plunge to freezing point. In contrast are the coastal regions of the country, where the warmth is unvarying and the rains are frequent. India, not only its physiographic divisions are diverse but also far more contrasting in nature. Each one of these factors (Size, Shape, location extent etc.,) has an impact on climatic conditions of India, be it temperatures, atmospheric pressure, wind system or precipitation.
Factors influencing the Indian climate Location and Latitudinal Extent
- The Tropic of Cancer passes through the middle of the country. The southern parts being closer to the Equator, experience high temperatures throughout.
- The northern parts on the other hand lie in the warm temperate Hence they experience low temperatures particularly, in winter.
- For example, Bangalore would be hotter than Faridabad. Broadly speaking parts lying south of the Tropic of Cancer receive more solar heat than those lying north of it.
Distance from the Sea
- Southern or peninsular India is surrounded by the Arabian Sea, the Indian Ocean and the Bay of Bengal, hence the climate of coastal regions of India is equable or maritime.
- Contrary to this, the climates of the regions located in the interior of the country are cut off from the oceanic influence. As a result, they have an extreme or continental type of climate.
- The atmosphere becomes less dense and temperature also decreases with the height. For example, the cities located on the hills are cooler like Shimla whereas the cities lying in the plains will have hot climate like Ludhiana.
- These ranges protect India from the bitterly cold and dry winds of Central Asia during winter. Further, they act as an effective physical barrier for the rain bearing southwest monsoons winds to cross the northern frontiers of India.
- On the other hand, they check rain bearing South-West Monsoon winds and compel them to shed their moisture in India.
- Similarly, Western Ghats force rain bearing winds to cause heavy rain fall on the Western slopes of the Western Ghats.
Direction of Surface Winds
- The wind system also affects the Indian climate. This system consists of monsoon winds, land and sea breeze, and local winds. In winter the winds blow from land to sea so they are cold and dry.
- On the other hand, in summer wind blow from sea to land bringing the moisture along with them from the sea and cause wide spread rain in most part of the country.
Upper air Currents
Besides surface winds, there are strong air currents called Jet streams which also influence the climate of India. These jet streams are a narrow belt of fast blowing winds located generally at 12,000 metre height above the sea level. They bring western cyclonic disturbances along with them. These cyclonic winds originate near the Mediterranean Sea and move eastwards. On their way, they collect moisture from Persian Gulf and shed it in the North western part of India during winter seasons. These Jet streams shift northwards during summer season and blow in Central Asia. Thus helps in the onset of monsoons.
The physical features influence the air temperature, atmospheric pressure, direction of winds and the amount of rainfall in different parts of the country.
El-Nino & La Nina
- Weather conditions in India are also influenced by El-Nino which causes wide spread floods and droughts in tropical regions of the world. This warming of tropical Pacific waters affects the global pattern of pressure and wind systems including the monsoon winds in the Indian Ocean. It is believed that the severest droughts in India have been caused by El-Nino.
- La Nina is thought to be favourable to India as it brings rains.
Monsoon and Seasons in India
The word monsoon is derived from the Arabic word ‘Mausim’ which means season. Monsoon refers to the seasonal reversal in the wind direction during a year. During summer, the interior parts of North Indian Plains covering Rajasthan, Punjab, Haryana, and Western Uttar Pradesh are intensely hot. The daily maximum temperature in some of these parts is as high as 45° to 47° C.
The average maximum temperature is above 33°C in the month of May at Delhi, Jodhpur and Jaisalmer. Such high temperature heats up the air of that region. Hot air rises and due to this a low pressure area is created under it. This low pressure is also known as monsoonal trough. It lies between western Rajasthan to Odisha.
On the other hand temperature over Indian Ocean is relatively low. So a relatively high pressure region is created over the sea.
The pressure difference between Indian Ocean and North Central Indian Plains causes the air from high pressure region of the sea move towards the low pressure region of North India. This implies that the general movement of air is in June is from equatorial region of Indian Ocean to the Indian subcontinent in the South-West to North-East direction. This direction is exactly opposite to that of the trade winds (North – East to South-West) prevailing during winter in India. This complete reversal of wind direction from North-East to South West and vice-versa is known as monsoons. The winds contain a lot of moisture. When these moisture laden winds move over the Indian sub- continent they cause wide spread rain throughout India and from June to September. Thus, most of the total rainfall in India is confined to these four months only.
During the winter season, North-East trade winds prevail over India. They blow from land to sea and that is why that for most part of the country, it is a dry season. A part of North-East trade winds blow over Bay of Bengal. They gather moisture which causes rainfall in the Coromandal coast while the rest of the country remains dry. Strictly speaking these winds are planetary winds known as Northeast Trades. In India they are essentially land bearing winds.
Irregularity of Monsoon
Monsoons winds are irregular in nature affected by different atmospheric conditions. They are also not equally distributed. Coastal areas like Kerala West Bengal and Odisha receive heavy rain fall, whereas interior regions like Haryana, Madhya Pradesh, receive less rainfall. When monsoon arrives, it gives heavy rainfall which continues for several days. This is known as ‘burst of monsoon’, which generally occurs at the Kerala coast. The monsoon tends to have ‘breaks’ in its rainfall which causes wet and dry spells. This means that monsoon rains occur only a few days at a time. Rainless dry spells occur in between. This simple story is based upon a mechanism proposed by Halley and is also known as Thermal Concept. However, it fails to answer the following questions:
- Why the low pressure areas on land are not stationary and why they suddenly change their location?
- Why there is no antimonsoon circulation in the upper troposphere, which must be there if the monsoon winds are thermally induced?
- Low Pressure are in northern India is in April and May, but rains start in the end of June or beginning of July.
- Monsoon rains are an amalgamation of convectional, orographic and cyclonic rainfall the thermal concept is unsatisfactory to explain in details.
Another gentleman Fohn tried to link the Monsoon with the ITCZ or Intertropical Convergence Zone, which is called Dynamic Concept.
This concept says that monsoon is the result of seasonal migration of planetary winds and pressure belts around Equator. The Inter-Tropical Convergence Zone (ITCZ) is formed due to the convergence of north-east and south-east trade winds near the equator. In summer when the rays of Sun are directly above the Tropic of Cancer, the Northern Intertropical Zone gets extended up to 30° N latitude, thus covers the South Asia as well as South East Asia, where a low pressure area develops.
When this happens, the trade winds of the Southern Hemisphere need to cross the equator in order to reach the ITCZ. Thus, the trade winds of the Southern Hemisphere cross the equator but are deflected towards right under the Coriolis Effect. In this manner a new belt of “equatorial westerlies” is developed and Indian landmass receives the south west monsoon due to these winds.
This theory further explains that in winter, the ITCZ shifts towards south of Equator and the North East Trade winds have to cross the equator to reach the ITCZ. These winds blowing from the northern hemisphere to southern hemisphere deflected left due to Coriolis Effect and blow as North westerly Monsoon there. Since the winds blowing over the Indian subcontinent at this time are usual trade winds of these latitudes, they blow from North East to South West and so become the North East Monsoon.
Seasons in India
There are four seasons in India viz. Winter (December-February), Hot weather summer (March- May), Rainy south-western monsoon (June-September) and Post-monsoon, also known as north- east monsoon in the southern Peninsula (October-November).
During the winter season, the temperature decreases with increasing latitude in India from 25°C in South to near zero temperature on north. This season is characterised by Fog and Frost in North and North-West India. There is light rainfall in this region due to Western disturbances. There is a sustained snowfall on the higher slopes of the Himalayas.
North East Monsoon
In India, rains occur in winter due to the North East Monsoon. During the winter season, North-East trade winds prevail over India. They blow from land to sea and that is why that for most part of the country, it is a dry season. A part of North-East trade winds blow over Bay of Bengal. They gather moisture which causes rainfall in the Coromandal coast while the rest of the country remains dry. In the northern part of the country the weather is marked by clear sky, low temperatures and low humidity. The winter rainfall is very important for the cultivation of ‘Rabi’ crops.
Impact of Jet streams in Winter
Jet streams are fast flowing, narrow air currents located near the Tropopause, the transition between the troposphere and the stratosphere. The major jet streams on Earth are westerly winds(flowing west to east). Their paths typically have a meandering shape; jet streams may start, stop, split into two or more parts, combine into one stream, or flow in various directions including the opposite direction of most of the jet.
The strongest jet streams are the polar jets, at around 7–12 km above sea level, and the higher and somewhat weaker subtropical jets at around 10–16 km. The Northern Hemisphere and the Southern Hemisphere each have both a polar jet and a subtropical jet. The northern hemisphere polar jet flows over the middle to northern latitudes of North America, Europe, and Asia and their intervening oceans, while the southern hemisphere polar jet mostly circles Antarctica all year round. The Jet streams are upper level, irregular, concentrated, meandering bands of westerly winds that travel at speeds of 300 to 400 kmph and come to India from the Mediterranean side in winter. This jet stream is bifurcated due to the physical obstruction of the Himalayas and Tibetan Plateau. One branch is located to the south of the Himalayas, while the second branch is positioned to the north of the Tibetan Plateau. The southern branch blows eastwards south of the Himalayan ranges along 25°N latitude (Rajasthan., MP, Chhattisgarh etc.) . These winds tend to descend over the north- western parts of India, resulting into the development of atmospheric stability and dry conditions. It is believed that this branch of jet stream exercises a significant influence on the winter weather conditions in India. This jet stream is responsible for bringing western disturbances from the Mediterranean region into Indian sub-continent. Winter rain and hail storms in north western plains and occasional heavy snowfall in hilly regions are caused by these disturbances. These are generally followed by cold waves in whole of northern plains.
Western Disturbances are basically the temperate cyclones that originate in the Mediterranean Sea and west Asia and happen to reach Afghanistan and Pakistan. In winters, they cross the North West borders of India and reach up to Central India. These disturbances bring small winter rains in India which are locally called Mahavat (Rajasthan, Haryana, Punjab) and are beneficial for the Rabi Crops. They also bring cold waves and snowfall in the higher altitudes of the Jammu and Kashmir and Himachal Pradesh.
By the end of February the temperature starts rising and there is a hot weather season in India from March to May. During these months the central part of peninsular India expiries extreme hot weather and an elongated low pressure belt which is called monsoonal trough created, which extends from Jaisalmer in western Rajasthan to Jharkhand and parts of Odisha to the East. However, over Indian Ocean south of the equator high pressure belt begins to develop in this season. In North-West India, afternoon dust storms are common. During summer, very hot and dry winds blow over North Indian plains. They are locally called ‘Loo’. At the same time, localized thunderstorms, associated with violent winds, torrential downpours, often accompanied by hail occur in many parts of India.
- In West Bengal, these storms are known as the ‘Kaal Baisakhi’ (calamity for the month of Baisakh).
- Towards the close of the summer season, pre-monsoon showers are common, especially in Kerala and Karnataka, which help in the early ripening of mangoes, and are often referred to as ‘mango showers’.
- The thunderstorms which occur during summer to bring some rainfall in Karnataka are also known as Cherry Blossom Showers.
Rainy south-western monsoon (June-September)
June to September are the months of advancing South-West monsoon season. By the end of May, the monsoon trough further intensifies over north India due to high temperature. The General direction of the wind during this season is from South-West to north-east. These winds are strong and blow at an average velocity of 30 km per hour. These moisture laden winds first hit at Andaman and Nicobar Islands in the last week of May and Kerala coast in the first week of June with violent thunder and lightning. This South-West monsoon that flows in to India brings about a major change in its weather. Two branches of south-west monsoon originate from:
- Arabian Sea
- Bay of Bengal.
The Arabian Sea Branch obstructed by Western Ghats gives heavy rainfall on the Western side of Western Ghats. It reaches Mumbai by 10th June. When this branch crosses the Western Ghats and reaches the Deccan Plateau and parts of Madhya Pradesh, it gives less rainfall as it is a rain shadow region. Further, this branch reaches in Northern Plain by 20th June.
The monsoon winds that move from Bay of Bengal strike Andaman and Nicobar Islands North- Eastern states and coastal areas of West Bengal and cover the whole of India by the 15th of July. They cause heavy rainfall in the region. However, quantity of rainfall decreases as they move towards West over the Northern plains. For examples rainfall at Kolkata is 120 cm, Allahabad 91 cm and Delhi 56cm.
Rains in Bangalore versus Mangalore
Bangalore receives less rainfall in comparison to Mangalore because Bangalore is located in the rain shadow (Leeward Side) of Western Ghats and when the wind blows from the west, it gets obstructed by the hills. Thus the moisture laden wind blows to the windward side of the ghats, causing heavy rainfall in the coastal region and ghat areas and the rainfall in Bangalore is limited. However, you must note here that during weak monsoon condition when there is ample sunshine, the lower levels of the atmosphere are warm which gives rise to convection current. The air goes up leading to the formation of clouds, resulting in rainfall in the city. Similarly, Pune receives less rainfall because it is also located on lewardside of western Ghats. Other examples are Shillong and Hyderabad. Shillong lies on the northern leeward slopes of the Khasi Hills and therefore receives less rain.
Post Monsoon Season
October and November are the months of post (or retreating) monsoon season. The temperatures during September-October start decreasing in north India. Monsoonal trough also becomes weak over North-West India. This is gradually replaced by a high pressure system. The South-West monsoon winds weaken and start withdrawing gradually from North Indian Plains by November. In October the weather remains humid and warm due to continuing high temperature and moist land in month of October. In Northern plains hot and humid weather becomes oppressive at this time. It is commonly called ‘October Heat’. However, towards the end of October, temperature starts decreasing, making nights pleasant.
By the month of November, the low pressure of North India shifts to Bay of Bengal and this is the time of cyclonic storms which develop in the Bay of Bengal. These storms create havoc in coastal areas of Odisha, Andhra Pradesh and Tamil Nadu, especially in the deltas of Mahanadi, Godavari and Krishna rivers.
Distribution of Rainfall in India
Rainfall in India is highly uneven over a period of time in a year. The western coasts and North East India receive rainfall of over 400 cm. It is less than 60 cms in western Rajasthan and adjoining parts of Gujarat, Haryana and Punjab. Similarly, rainfall is low in the interiors of the Deccan Plateau and east of Western Ghats. Then, Leh in Jammu and Kashmir is also an area of low precipitation.
Here are some more observations about distribution of rainfall in India
- As we move from Meghalaya to Haryana or Punjab in Northern plains, we observe that the rainfall decreases.
- In peninsular India, rainfall decreases from coast to interior parts.
- In North-East India, the rainfall increases with altitude.
- Maximum rainfall (above 200 cms) in India occurs in the western coast, sub Himalayan regions of north-east and Garo, Khasi and Jaintia hills of Meghalaya.
- Moderate rainfall (100-200cm) occurs in some parts of the Western Ghats, West Bengal, Odisha and Bihar and many states.
- Low rainfall (60 to 100cm) occurs in parts of Uttar Pradesh, Rajasthan, and interior Deccan plateau.
- Inadequate rainfall (Less than 60cm) occurs in western part of Rajasthan and Gujarat, Ladakh and south central part receives a rainfall of less than 20cm.
Impact of El Niño/La Niña–Southern Oscillation
A recurring characteristic of the climate is called Climatic Pattern. The gap between two recurrences may be from one year to as long as tens of thousands of years. Some of the events are in regular cycle, while some are not. When they recur in the form of regular cycles of fluctuations in climate parameters, they are called climate oscillations. The term oscillation is used because such fluctuations are not perfectly periodic. For example, we say that El Nino returns every four and half years. But actually it may or may not return. Or it may return too early or too late. So, El Nino is quasi periodic.
El Niño was originally recognized by fisherman off the coast of Peru in South America. The ocean off the coast of Peru is one of the world’s richest fisheries regions. In most years trade winds flow from the southeast push warm surface water away from the coast. In its place, the cold water comes up on the surface due to upwelling. This cold water is full of nutrients and provides nourishments to planktons. These planktons serve as food for fishes. Fishes in turn provide food to the sea birds. Due to all this, not only there is a good catch of fishes but also good collection of the Guano, the bird excreta, used as a valuable fertilizer. This is what that made Peru number one fishing nation in the world by the early 1970s.
However, every few years, there is a change in the pattern of air circulation. It changes in such a way that the trade winds reverse direction, blowing from west to east. Due to this reversal, the upwelling of the cold water gets weakened. The surface water is warm. This lowers the nutrients available to fish and thus poses problems to the economics of fisheries. The problems don’t end here. The accumulation of large mass of warm water allows formation of more and more clouds and this would bring destructive rains that occur in normally dry areas of Peru and Chile. The same is also responsible for bring outbreaks of Malaria and Cholera in some parts of South America. Peru , as you may know is a Hispanophone country as many people speak Spanish out there. The above mentioned reversal of the winds occurred during Christmas times (Please note that we have Christmas in winter, but Peruvians have in summer, because they are in southern hemisphere), so they named it El Niño or “Christ Child” or “The Little Boy” in their own language. Before, you read further, please understand the location of Eastern, Central and Western Pacific on the map, otherwise it would be too confusing (earth is round…after all)
Now, here is how it affects the entire tropical region.
- Off the coast of Peru (read in Eastern Pacific and Central Pacific), there is normally cool surface water. But El Niño makes it go warm. When the water becomes warm, the tread winds, which otherwise flow from East to west, either reverse their direction or get lost. The warm water causes lots of clouds getting formed in that area, causing heavy rains in Peruvian desert during El Niño years.
- Due to this warm water, the air gets up and surface air pressure above Eastern Pacific gets down. On the other hand, the waters cool off in western pacific and off Asia. This leads to rise in surface pressure over the Indian Ocean, Indonesia, and Australia
- So, while there is raining (read flooding) in Eastern Pacific; the drought sets in over Asia as high pressure builds over the cooler ocean waters.
- The net result is: Normal or high rainfall in eastern / central pacific. Drought or scant rainfall in western pacific / Asia.
Although El Niño originally referred to local conditions off the coast of Peru and Ecuador, the use of the term has been broadened by many scientists to represent all surface temperature warming in the eastern and central Pacific. The impacts of El Niño , which have been well documented include the following:
- Heavy rains in Ecuador and Peru.
- Heavy rains in southern Brazil but drought in north East Brazil
- Drought in Zimbabwe, Mozambique, South Africa, Ethiopia
- Warm winter in the northern half of the United States and southern Canada
- Drought, Scant rains off Asia including India, Indonesia, and Philippines etc.
- Coral bleaching worldwide
- Drought in eastern Australia
La Niña, which means “The Little Girl” or “El Viejo” or “anti-El Niño” or simply “a cold event” or “a cold episode is the cooling of water in the Eastern Pacific Ocean. Here is what happens in La Niña.
- The water in Eastern Pacific, which is otherwise cool; gets colder than normal. There is no reversal of the trade winds but it causes strong high pressure over the eastern equatorial Pacific.
- On the other hand, low pressure is caused over Western Pacific and Off Asia.
- This has so far caused the following major effects:
- Drought in Ecuador and Peru. Low temperature, High Pressure in Eastern Pacific
- Heavy floods in Australia; High Temperature in Western Pacific, Indian Ocean, Off coast Somalia and good rains in India.
- Drought in East Africa (Somalia Drought of 2011 was linked to it)
Both El Nino and La Nina are part of a larger cycle called ENSO, or El Niño–Southern Oscillation. The El Niño (warm event) and La Nina (Cold event) both have now established themselves as the integral part of the global climate system. It is a recurrent phenomenon with an average return period of 41/2 years, but can recur as little as 2 or as much as 10 years apart. Such events have occurred for millennia, and can be expected to continue to occur in the future.
Impact of El Niño and La Nina on Indian Weather
- El Nino and La Nina are among the most powerful phenomenon on the Earth. These are known to alter climate across more than half the planet and dramatically impact weather patterns.
- Over Indian subcontinent, El Nino during winter results in development of warm conditions. During summer, it leads to dry conditions and deficient monsoon. It also leads to drought in Australia. On the other hand, La Nina results in better than normal monsoon in India. At the same time, in Australia it has caused floods.
- In the recent past, India experienced deficient rainfall during El Nino years 2002 and 2009 whereas monsoon was normal during El Nino years 1994 and 1997. This so far implies that in about 50 per cent of the years with El Nino during summer, India experienced droughts during monsoon.
- This implies that El Nino is not the only factor that affects monsoon in India. There are other factors that affect India’s rainfall pattern. These include North Atlantic SST, Equatorial SE Indian Ocean SST, East Asia Mean Sea Level Pressure, North Atlantic Mean Sea Level Pressure and North Central Pacific wind at 1.5 km above sea level.
Difference between El Nino and La Nina
|El Nino is a Spanish term which represents “little boy”||La Nina is a Spanish term which represents ‘little girl’.|
|Temperature at Sea Surface
|Temperature at sea surface is warmer than normal sea-surface temperatures. El Nino is a warming of the Paciﬁc Ocean between South America and the Date Line, centred directly on the Equator, and typically extending several degrees of latitude to either side of the equator.
|Temperature at sea surface is cooler than normal sea-surface temperatures. La Nina exists when cooler than usual ocean temperatures occur on the equator between South America and the Date Line.
|Pressure||It accompanies high air surface pressure in the western Paciﬁc
|accompanies low air surface pressure in the eastern Paciﬁc
|El Niño occurs when tropical Paciﬁc Ocean trade winds die out and ocean temperatures become unusually warm
|La Nina, which occurs when the trade winds blow unusually hard and the sea temperature become colder than normal
|Winters are warmer and drier than average in the Northwest of paciﬁc, and wetter in Southwest of paciﬁc and experience reduced snowfalls.
|Winters are wetter and cause above- average precipitation across the Northwest of paciﬁc and drier and below average precipitation in South west of paciﬁc.
|El Nino results in a decrease in the earth’s rotation rate (very minimal) , an increase in the length of day, and therefore a decrease in the strength of the Coriolis force
|La Nino results in increase in the earth’s rotation rate, decrease in the length of day, and therefore a increase in the strength of the Coriolis force.
|Ocean waters in Paciﬁc
|Warm water approaches the coasts of South America which results in reduced upwelling of nutrient-rich deep water impacting impacts on the ﬁsh populations.
|Cold water causes increased upwelling of deep cold ocean waters numbers of drought occurrence, with more nutrient- ﬁlled eastern Paciﬁc waters.
|Cyclones||Comparatively less compared to La Niña as wind speed is low
|La Nina had a greater tendency to trigger intense tropical cyclones as wind direction changes pilling up water between Indonesia and nearby areas as winds from Africa onwards gets blocked.|
Do El Nino and La Nina explain most of the unusual climatic happenings?
It is undeniable that the El Nino has been used to explain unusual climatic changes across the globe. But, modern climatology taken into account various other phenomena also. However, El-Nino has far-reaching and varied effect on climate across the world. The major reason for these unusual climatic happenings is the shifting in tropical rainfall, which in turn affect the wind patterns across the world. When the El-Nino effect causes the rainy areas centered around Indonesia and the Pacific region to move eastward, the subsequent changes result in unseasonable weather in many regions of the world. The El Nino is typically characterized by warm ocean currents and heavy rains, however, it also plays havoc with the normal weather conditions in different areas of the world. Also, the increase in temperatures affects fishing adversely, disrupts local weather and indigenous marine life in the areas concerned, other than having an effect on climatic conditions worldwide. When the linkage between El Nino and climate effects were initially suggested by the British scientist, Gilbert Walker, it was deemed ridiculous that one phenomenon could have an effect on regions as far off as Australia, India etc and Canada. However, the occurrence of El Nino in the past few decades has proved without a doubt, their far-reaching consequences. Some of the effects of El Nino in the past have been causing of droughts and forest fires in South Asia (Indonesia and Philippines) and Australia, floods in the South American countries in the eastern Pacific region, increased rain in certain other areas of the world etc.