Theclimate of India includes a wide range of weather conditions, influenced by its vast geographic scale and varied topography. Based on theKöppen system,India encompasses a diverse array of climatic subtypes. These range from arid and semi-arid regions in the west to highland, sub-arctic, tundra, and ice cap climates in the northernHimalayan regions, varying with elevation.
TheIndo-Gangetic Plains in thenorth experience ahumid subtropical climate which become moretemperate at higher altitudes, like theSivalik Hills, orcontinental in some areas likeGulmarg. In contrast, much of the south and the east exhibittropical climate conditions, which support lush rainforests in parts of these territories. Many regions have starkly differentmicroclimates, making it one of the most climatically diverse countries in the world. The country's meteorological department follows four seasons with some local adjustments: winter (December to February), summer (March to May), monsoon or south-west monsoon (June to September) and post-monsoon or north-east monsoon (October to November). Some parts of the country with subtropical, temperate or continental climates also experience spring and autumn.
India'sgeography andgeology are climatically pivotal: theThar Desert in the northwest and theHimalayas in the north work in tandem to create aculturally andeconomically important monsoonal regime. As Earth's highest and most massive mountain range, the Himalayas bar the influx of frigidkatabatic winds from the icyTibetan Plateau and northerly Central Asia. Most ofNorth India is thus kept warm or is only mildly chilly or cold during winter; the same thermal dam keeps most regions in India hot in summer. The climate inSouth India is generally warmer, and more humid due to its coastlines. However some hill stations in South India such asOoty are well known for their cold climate.
Though theTropic of Cancer—the boundary that is between the tropics and subtropics—passes through the middle of India, the bulk of the country can be regarded as climatically tropical. As in much of the tropics, monsoonal and other weather patterns in India can be strongly variable: epochal droughts, heat waves, floods, cyclones, and other natural disasters are sporadic, but have displaced or ended millions of human lives. Such climatic events are likely tochange in frequency and severity as a consequence of human-inducedclimate change. Ongoing and future vegetative changes,sea level rise and inundation of India's low-lying coastal areas are also attributed to global warming.[2]
During theTriassic period of 251–199.6Ma, the Indian subcontinent was the part of a vastsupercontinent known asPangaea. Despite its position within a high-latitude belt at 55–75° S—latitudes now occupied by parts of theAntarctic Peninsula, as opposed to India's current position between 8 and 37° N—India likely experienced a humid temperate climate with warm and frost-free weather, though with well-defined seasons.[3] India later merged into the southern supercontinentGondwana, a process beginning some 550–500 Ma. During the LatePaleozoic, Gondwana extended from a point at or near theSouth Pole to near the equator, where theIndian craton (stablecontinental crust) was positioned, resulting in a mild climate favorable to hosting high-biomassecosystems. This is underscored by India's vast coal reserves—much of it from the late Paleozoic sedimentary sequence—the fourth-largest reserves in the world.[4] During theMesozoic, the world, including India, was considerably warmer than today. With the coming of theCarboniferous,global cooling stoked extensiveglaciation, which spread northwards from South Africa towards India; this cool period lasted well into thePermian.[5]
Tectonic movement by theIndian Plate caused it to pass over a geologichotspot—theRéunion hotspot—now occupied by the volcanic island ofRéunion. This resulted in a massiveflood basalt event that laid down theDeccan Traps some 60–68 Ma,[6][7] at the end of theCretaceous period. This may have contributed to the globalCretaceous–Paleogene extinction event, which caused India to experience significantly reducedinsolation. Elevated atmospheric levels of sulphur gases formedaerosols such assulphur dioxide andsulphuric acid, similar to those found in theatmosphere of Venus; these precipitated asacid rain. Elevatedcarbon dioxide emissions also contributed to thegreenhouse effect, causingwarmer weather that lasted long after the atmospheric shroud of dust and aerosols had cleared. Further climatic changes 20 million years ago, long after India had crashed into theLaurasian landmass, were severe enough to cause the extinction of many endemic Indian forms.[8] The formation of the Himalayas resulted in blockage of frigid Central Asian air, preventing it from reaching India; this made its climate significantly warmer and more tropical in character than it would otherwise have been.[9]
More recently, in theHolocene epoch (4,800–6,300 years ago), parts of what is now the Thar Desert were wet enough to support perennial lakes; researchers have proposed that this was due to much higher winter precipitation, which coincided with stronger monsoons.[10] Kashmir's erstwhile subtropical climate dramatically cooled 2.6–3.7 Ma and experienced prolonged cold spells starting 600,000 years ago.[11]
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India has many different climates, from tropical in the south to temperate and alpine in the Himalayan north, where higher areas get snowfall in winter. The nation's climate is strongly influenced by the Himalayas and the Thar Desert.[13] The Himalayas, along with theHindu Kush mountains in Pakistan, prevent cold Central Asian katabatic winds from blowing in, keeping the bulk of the Indian subcontinent warmer than most locations at similarlatitudes.[14] Simultaneously, the Thar Desert plays a role in attracting moisture-laden south-west monsoon winds between June and October, which provide the majority of India's rainfall.[13][15] Four major climatic groupings predominate, into which fall the seven climatic zones, that as designated by experts, are defined on the basis of such traits as temperature and precipitation.[16] Groupings are assigned codes (see chart) according to the Köppen climate classification system.
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A tropical rainy climate governs regions experiencing persistent warm or high temperatures, which normally do not fall below 18 degrees Celsius (64 °F). India predominantly hosts two climatic subtypes that fall into this group:tropical monsoon climate andtropical savanna climate.
The most humid is the tropical wet climate—also known as thetropical monsoon climate—that covers a strip of southwestern lowlands abutting theMalabar Coast, theWestern Ghats, and southernAssam. India's two island territories,Lakshadweep and theAndaman and Nicobar Islands, are also subject to this climate. Characterised by moderate to high year-round temperatures, even in the foothills, its rainfall is seasonal but heavy—typically above 2,000 millimetres (79 inches) per year.[17] Most rainfall occurs between May and November; this moisture is enough to sustain lush forests, swampy areas and other vegetation for the rest of the mainly dry year. December to March are the driest months, when days with precipitation are rare. The heavy monsoon rains are responsible for the exceptional biodiversity of tropical wet forests in parts of these regions.
In India atropical savanna climate is more common. Noticeably drier than areas with a tropical monsoon type of climate, it prevails over most of inland peninsular India except for a semi aridrain shadow east of the Western Ghats. Winter and early summer are long and dry periods with temperatures averaging above 18 °C (64 °F). Summer is exceedingly hot; temperatures in low-lying areas may exceed 50 °C (122 °F) during May, leading to heat waves that can each kill hundreds of Indians.[18] The rainy season lasts from June to September; annual rainfall averages between 750 and 1,500 mm (30 and 59 in) across the region. Once the dry northeast monsoon begins in September, most significant precipitation in India falls onTamil Nadu andPuducherry leaving other states comparatively dry.
TheGanges Delta lies mostly in the tropical wet climate zone: it receives between 1,500 and 2,000 mm (59 and 79 in) of rainfall each year in the western part, and 2,000 and 3,000 mm (79 and 118 in) in the eastern part. The coolest month of the year, on average, is January; April and May are the warmest months. Average temperatures in January range from 14 to 25 °C (57 to 77 °F), and average temperatures in April range from 25 to 35 °C (77 to 95 °F). July is on average the coldest and wettest month: over 330 mm (13 in) of rain falls on the delta.[19]
Additionally,Nicobar Islands rain forests experience aTropical rainforest climate.[20]
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Arid andsemi-arid climate dominates regions where the rate of moisture loss throughevapotranspiration exceeds that from precipitation;
A semi-arid steppe climate (hot semi-arid climate) predominates over a long stretch of land south of Tropic of Cancer and east of theWestern Ghats and theCardamom Hills. The region, which includesKarnataka, inlandTamil Nadu, westernAndhra Pradesh, and centralMaharashtra, gets between 400 and 750 millimetres (15.7 and 29.5 in) annually. It is drought-prone, as it tends to have less reliable rainfall due to sporadic lateness or failure of the southwest monsoon.[21] Karnataka is divided into three zones—coastal, north interior and south interior. Of these, the coastal zone receives the most precipitation, averaging 3,638 mm (143.2 in) per annum, far in excess of the state average of 1,139 mm (44.8 in). In contrast to norm,Agumbe in the Shivamogga district receives the second highest annual rainfall in India. North of theKrishna River, the summer monsoon is responsible for most rainfall; to the south, significant post-monsoon rainfall also occurs in October and November. In December, the coldest month, temperatures still average around 20–24 °C (68–75 °F). The months between March and May are hot and dry; mean monthly temperatures hover around 32 °C (90 °F), with 320 millimetres (12.6 in) precipitation. Hence, without artificial irrigation, this region is not suitable for permanent agriculture.[citation needed]
Most of westernRajasthan experiences an arid climatic regime (hot desert climate).Cloudbursts are responsible for virtually all of the region's annual precipitation, which totals less than 300 millimetres (11.8 in). Such bursts happen when monsoon winds sweep into the region during July, August, and September. Such rainfall is highly erratic; regions experiencing rainfall one year may not see precipitation for the next couple of years or so. Atmospheric moisture is largely prevented from precipitating due to continuousdowndrafts and other factors.[22] The summer months of May and June are exceptionally hot; mean monthly temperatures in the region hover around 35 °C (95 °F), with daily maxima occasionally topping 50 °C (122 °F). During winters, temperatures in some areas can drop below freezing due to waves of cold air from Central Asia. There is a large diurnal range of about 14 °C (25 °F) during summer; this widens by several degrees during winter. There is a small desert area in the south nearAdoni in Andhra Pradesh, the only desert inSouth India, experiencing maximum temperatures of 47 °C (117 °F) in summers and 18 °C (64 °F) in winters.[citation needed]
To the west, inGujarat, diverse climate conditions prevail. The winters are mild, pleasant, and dry with average daytime temperatures around 29 °C (84 °F) and nights around 12 °C (54 °F) with virtually full sun and clear nights. Summers are hot and dry with daytime temperatures around 41 °C (106 °F) and nights no lower than 29 °C (84 °F). In the weeks before the monsoon temperatures are similar to the above, but high humidity makes the air more uncomfortable. Relief comes with the monsoon. Temperatures are around 35 °C (95 °F) but humidity is very high; nights are around 27 °C (81 °F). Most of the rainfall occurs in this season, and the rain can cause severe floods. The sun is often occluded during the monsoon season.[citation needed]
East of theThar Desert, the SouthwestPunjab–WestHaryana–Kathiawar region experiences a tropical and sub-tropical steppe climate. Haryana's climate resembles other states of the northern plains: extreme summer heat of up to 45 °C (113 °F) and winter cold as low as 0 °C (32 °F). May and June are hottest; December and January are coldest. Rainfall is varied, with theShivalik Hills region being the wettest and theBagar region being the driest. About 80 percent of the rainfall occurs in the monsoon season of July–September, which can cause flooding. The Punjabi climate is also governed by extremes of hot and cold. Areas near theHimalayan foothills receive heavy rainfall whereas those eloigned from them are hot and dry. Punjab's three-season climate sees summer months that span from mid-April to the end of June. Temperatures in Punjab typically range from −2 to 40 °C (28–104 °F), but can reach 47 °C (117 °F) in summer and fall to −4 °C (25 °F) in winter (while most of the nation does not experience temperatures below 10 °C (50 °F) even in winter). The zone, a transitional climatic region separating tropical desert from humid subtropical savanna and forests, experiences temperatures that are less extreme than those of the desert. Although the average annual rainfall is 300–650 millimetres (11.8–25.6 in), it is very unreliable; like in much of the rest of India, the southwest monsoon accounts for most precipitation. Summer daily maxima are around 40 °C (104 °F). All t his results in a natural vegetation typically comprising short, coarse grasses.[citation needed]
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Most ofNortheast India and much of North India are subject to ahumid subtropical climate and asubtropical highland climate. Though they experience warm to hot summers, temperatures during the coldest months generally fall as low as 0 °C (32 °F). Due to ample monsoon rains, India has two subtropical climate subtypes under theKöppen system:Cwa andCwb.[23] In most of this region, there is very little precipitation during the winter, owing to powerful anticyclonic andkatabatic (downward-flowing) winds from Central Asia.
Humid subtropical regions are subject to pronounced dry winters. Winter rainfall and hail—is associated with largeextratropical storms known as "Western disturbances", which are steered bywesterlies towards the Himalayas and thePunjab-Haryana Plains of northwestern India.[24] Most summer rainfall occurs during powerfulmesoscale convective thunderstorms known asnor'westers in the pre-monsoon season (April-June) andmonsoonalthunderstorms brought by theSouth Asian monsoon (July-September); occasionaltropical cyclones also contribute. Annual rainfall ranges from less than 1,000 millimetres (39 in) in the west to over 2,500 millimetres (98 in) in parts of the northeast. As most of this region is far from the ocean, the wide temperature swings more characteristic of acontinental climate predominate; the swings are wider than in those in tropical wet regions, ranging from 24 °C (75 °F) in the north to 27 °C (81 °F) in the east.[citation needed] The primarybiome of this climatic region issubtropical broadleaf forest, which isevergreen in theBrahmaputra Valley, and theLower Gangetic Plains which receive more rainfall, ordeciduous in theUpper Gangetic Plains andPunjab-Haryana Plains which receive comparatively less rainfall. This climate zone is home to many major cities ofNorth andNortheast India such asNew Delhi (bordering on semi-arid),Lucknow,Ambala,Chandigarh,Patiala,Siliguri andGuwahati (bordering on tropical savanna).
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India's northernmost areas are subject to a montane, or alpine, climate. In the Himalayas, the rate at which an air mass's temperature falls per kilometre (3,281 ft) of altitude gained (thedry adiabatic lapse rate) is 9.8 °C/km.[25] In terms ofenvironmental lapse rate, ambient temperatures fall by 6.5 °C (11.7 °F) for every 1,000 metres (3,281 ft) rise in altitude. Thus, climates ranging from nearly tropical in the foothills to tundra above thesnow line can coexist within several hundred metres of each other. Sharp temperature contrasts between sunny and shady slopes, high diurnal temperature variability, temperature inversions, and altitude-dependent variability in rainfall are also common.
The northern side of the western Himalayas, also known as the trans-Himalayan belt, has acold desert climate. It is a region of barren, arid, frigid and wind-blown wastelands. Areas south of the Himalayas are largely protected from cold winter winds coming in from the Asian interior. The leeward side (northern face) of the mountains receives less rain.
The southern slopes of the western Himalayas, well-exposed to the monsoon, get heavy rainfall. Areas situated at elevations of 1,070–2,290 metres (3,510–7,510 ft) receive the heaviest rainfall, which decreases rapidly at elevations above 2,290 metres (7,513 ft). Most precipitation occurs as snowfall during the late winter and spring months. The Himalayas experience their heaviest snowfall between December and February and at elevations above 1,500 metres (4,921 ft). Snowfall increases with elevation by up to several dozen millimetres per 100 metre (~2 in; 330 ft) increase. Elevations above 6,000 metres (19,685 ft) never experience rain; all precipitation falls as snow.[26]
TheIndia Meteorological Department (IMD) designates four climatological seasons:[27]
The Himalayan andUpper Gangetic Plains, being more temperate, experience an additional season,spring, which coincides with the first weeks of summer in southern India.[28] Traditionally, North Indians note six seasons orRitu, each about two months long. These are the spring season (Sanskrit:vasanta), summer (grīṣma), monsoon season (varṣā), autumn (śarada), winter (hemanta), and prevernal season[29] (śiśira). These are based on the astronomical division of the twelve months into six parts. The ancientHindu calendar also reflects these seasons in its arrangement of months.
The word Kālam or paruvam is the word for season in tamil standard.These words are generally derived fromproto dravidian and is continuosly used till today to refer seasons which is independent to that of sanskrit. It's not present in other south indian languages but some village dialects ofmalayalam.
Once the monsoons subside, average temperatures gradually fall across India. As the Sun's vertical rays move south of the equator, most of the country experiences moderately cool weather. December and January are the coldest months, with the lowest temperatures occurring in the Indian Himalayas. Temperatures are higher in the east and south.
In northwestern India region, virtually cloudless conditions prevail in October and November, resulting in wide diurnal temperature swings; as in much of the Deccan Plateau, they register at 16–20 °C (61–68 °F). However, from January to February, "western disturbances" bring heavy bursts of rain and snow. These extra-tropicallow-pressure systems originate in the eastern Mediterranean Sea.[30] They are carried towards India by the subtropicalwesterlies, which are the prevailing winds blowing at North India's range of latitude.[24] Once their passage is hindered by the Himalayas, they are unable to proceed further, and they release significant precipitation over the southern Himalayas.
There is a huge variation in the climatic conditions of Himachal Pradesh due to variation in altitude (450–6500 metres). The climate varies from hot and subtropical humid (450–900 metres) in the southern low tracts, warm and temperate (900–1800 metres), cool and temperate (1900–2400 metres) and cold glacial and alpine (2400–4800 metres) in the northern and eastern elevated mountain ranges. By October, nights and mornings are very cold. Snowfall at elevations of nearly 3000 m is about 3 m and lasts from December start to March end. Elevations above 4500 m support perpetual snow. The spring season starts from mid February to mid April. The weather is pleasant and comfortable in the season. The rainy season starts at the end of the month of June. The landscape lushes green and fresh. During the season streams and natural springs are replenished. The heavy rains in July and August cause a lot of damage resulting in erosion, floods and landslides. Out of all the state districts, Dharamshala receives the highest rainfall, nearly about 3,400 mm (134 in). Spiti is the driest area of the state, where annual rainfall is below 50 mm.[31] The five Himalayan states (Ladakh, Jammu and Kashmir in the extreme north, Himachal Pradesh, Uttarakhand, Sikkim and Arunachal Pradesh in far east) and Northern West Bengal experience heavy snowfall, Manipur and Nagaland are not located in the Himalayas but experience occasional snowfall; in Ladakh, Himachal Pradesh and Jammu and Kashmir,blizzards occur regularly, disrupting travel and other activities.
The rest of North India, including theIndo-Gangetic Plain andMadhya Pradesh almost never receives snow. Temperatures in the plains occasionally fall below freezing, though never for more than one or two days. Winter highs in Delhi range from 16 to 21 °C (61 to 70 °F). Nighttime temperatures average 2–8 °C (36–46 °F). In the plains of Punjab, lows can fall below freezing, dropping to around −3 °C (27 °F) inAmritsar.[32] Frost sometimes occurs, but the hallmark of the season is the notorious fog, which frequently disrupts daily life; fog grows thick enough to hinder visibility and disrupt air travel 15–20 days annually. In Bihar in middle of the Ganges plain, hot weather sets in and the summer lasts until the middle of June. The highest temperature is often registered in late May or early June which is the hottest time. Like the rest of the north, Bihar also experiences dust-storms, thunderstorms and dust raising winds during the hot season. Dust storms having a velocity of 48–64 km/h (30–40 mph) are most frequent in May and with second maximum in April and June. The hot winds (loo) ofBihar plains blow during April and May with an average velocity of 8–16 km/h (5–10 mph). These hot winds greatly affect human comfort during this season. Rain follows.[33] The rainy season begins in June. The rainiest months are July and August. The rains are the gifts of the southwest monsoon. There are in Bihar three distinct areas where rainfall exceeds 1,800 mm (71 in). Two of them are in the northern and northwestern portions of the state; the third lies in the area aroundNetarhat. The southwest monsoon normally withdraws from Bihar in the first week of October.[34] Eastern India's climate is milder but gets colder as one moves north west, experiencing moderately warm days to cool days and cool nights to cold nights. Highs ranges from 18 °C to 23 °C (64 °F to 73 °F) inPatna; to 22 °C to 27 °C (72 °F to 80 °F) inKolkata (Calcutta); lows averages from 7 °C to 10 °C (45 °F to 50 °F) in Patna; to 12 °C to 15 °C (54 °F to 59 °F) in Kolkata. In Madhya Pradesh which is towards the south-western side of the Gangetic Plain similar conditions prevail albeit with much less humidity levels. CapitalBhopal averages low of 9 °C (48 °F) and high of 24 °C (75 °F).
Frigid winds from the Himalayas can depress temperatures near theBrahmaputra River.[35] The Himalayas have a profound effect on the climate of the Indian subcontinent and the Tibetan plateau by preventing frigid and dry Arctic winds from blowing south into the subcontinent, which keeps South Asia much warmer than corresponding temperate regions in the other continents. It also forms a barrier for themonsoon winds, keeping them from travelling northwards, and causing heavy rainfall in theTerai region instead. The Himalayas are indeed believed to play an important role in the formation of Central Asian deserts such as theTaklamakan andGobi. The mountain ranges prevent western winter disturbances in Iran from travelling further east, resulting in much snow in Kashmir and rainfall for parts ofPunjab and northern India. Despite the Himalayas being a barrier to the cold northerly winter winds, the Brahmaputra valley receives part of the frigid winds, thus lowering the temperature in Northeast India and Bangladesh. The Himalayas contain the greatest area of glaciers and permafrost outside of the poles, and account for the origin of ten of Asia's largest rivers. The two Himalayan states in the east, Sikkim and Arunachal Pradesh, receive substantial snowfall. The extreme north ofWest Bengal centred onDarjeeling experiences snowfall, but only rarely.
InSouth India, particularly the hinterlands of Maharashtra, parts of Karnataka, and Andhra Pradesh, somewhat cooler weather prevails. Minimum temperatures in eastern Maharashtra andChhattisgarh hover around 10 °C (50 °F); in the southern Deccan Plateau, they reach 16 °C (61 °F). Coastal areas—especially those near theCoromandel Coast and adjacent low-elevation interior tracts—are warm, with daily high temperatures of 30 °C (86 °F) and lows of around 21 °C (70 °F). The Western Ghats, including theNilgiri Range, are exceptional; lows there can fall below freezing.[36] This compares with a range of 12–14 °C (54–57 °F) on the Malabar Coast; there, as is the case for other coastal areas, the Indian Ocean exerts a strong moderating influence on weather.[14] The region averages 800 millimetres (31 in)
Summer in northwestern India starts from mid-April and ends in late-June, and in the rest of the country from March to May but sometimes lasts to mid June. The temperatures in the north rise as the vertical rays of the Sun reach the Tropic of Cancer. The hottest month for the western and southern regions of the country is April; for most of North India, it is May and June. Temperatures of 50 °C (122 °F) and higher have been recorded in parts of India during this season. Another striking feature of summer is theLoo. These are strong, gusty, hot, dry winds that blow during the day in India. Direct exposure to the heat that comes with these winds may be fatal.[18] In many regions of North India, immense pre-monsoonsquall-line thunderstorms, known locally as "Nor'westers", commonly drop large hailstones. In Himachal Pradesh, Summer lasts from mid April till the end of June and most parts become very hot (except inalpine zone which experience mild summer) with the average temperature ranging from 28 °C (82 °F) to 32 °C (90 °F).[37] Near the coast, the temperature hovers around 36 °C (97 °F), and the proximity of the sea increases the level of humidity. In southern India, the temperatures are higher on the east coast by a few degrees compared to the west coast.
By May, most of the Indian interior experiences mean temperatures over 32 °C (90 °F), while maximum temperatures often exceed 40 °C (104 °F). In the hot months of April and May, western disturbances, with their cooling influence, may still arrive, but rapidly diminish in frequency as summer progresses.[38] Notably, a higher frequency of such disturbances in April correlates with a delayed monsoon onset (thus extending summer) in northwest India. In eastern India, monsoon onset dates have been steadily advancing over the past several decades, resulting in shorter summers there.[24]
Altitude affects the temperature to a large extent, with higher parts of theDeccan Plateau and other areas being relatively cooler.Hill stations, such asOotacamund ("Ooty") in the Western Ghats andKalimpong in the eastern Himalayas, with average maximum temperatures of around 25 °C (77 °F), offer some respite from the heat. At lower elevations, in parts of northern and western India, a strong, hot, and dry wind known as the loo blows in from the west during the daytime; with very high temperatures, in some cases up to around 45 °C (113 °F); it can cause fatal cases ofsunstroke.Tornadoes may also occur, concentrated in a corridor stretching from northeastern India towards Pakistan. They are rare, however; onlyseveral dozen have been reported since 1835.
The southwest summer monsoon, a four-month period when massive convective thunderstorms dominate India's weather, is Earth's most productive wet season.[39] A product of southeasttrade winds originating from a high-pressure mass centred over the southern Indian Ocean, the monsoonal torrents supply over 80% of India's annual rainfall.[40] Attracted by a low-pressure region centred over South Asia, the mass spawns surface winds that ferry humid air into India from the southwest.[41] These inflows ultimately result from a northward shift of the local jet stream, which itself results from rising summer temperatures overTibet and the Indian subcontinent. The void left by the jet stream, which switches from a route just south of the Himalayas to one tracking north of Tibet, then attracts warm, humid air.[42]
The main factor behind this shift is the high summer temperature difference between Central Asia and the Indian Ocean.[43] This is accompanied by a seasonal excursion of the normally equatorialintertropical convergence zone (ITCZ), a low-pressure belt of highly unstable weather, northward towards India.[42] This system intensified to its present strength as a result of theTibetan Plateau'suplift, which accompanied theEocene–Oligocene transition event, a major episode of global cooling andaridification which occurred 34–49 Ma.[44]
The southwest monsoon arrives in two branches: theBay of Bengal branch and theArabian Sea branch. The latter extends towards a low-pressure area over the Thar Desert and is roughly three times stronger than the Bay of Bengal branch. The monsoon typically breaks over Indian territory by around 25 May, when it lashes theAndaman and Nicobar Islands in the Bay of Bengal. It strikes the Indian mainland around 1 June near theMalabar Coast of Kerala.[45] By 9 June, it reaches Mumbai; it appears over Delhi by 29 June. The Bay of Bengal branch, which initially tracks the Coromandel Coast northeast fromCape Comorin to Orissa, swerves to the northwest towards theIndo-Gangetic Plain. The Arabian Sea branch moves northeast towards the Himalayas. By the first week of July, the entire country experiences monsoon rain; on average, South India receives more rainfall than North India. However,Northeast India receives the most precipitation. Monsoon clouds begin retreating from North India by the end of August; it withdraws from Mumbai by 5 October. As India further cools during September, the southwest monsoon weakens. By the end of November, it has left the country.[42]
Monsoon rains affect the health of theIndian economy; asIndian agriculture employs 600 million people and constitutes 20% of the national GDP,[4] good monsoons correlate with a booming economy. Weak or failed monsoons (droughts) result in widespread agricultural losses and substantially hinder overall economic growth.[46][47][48] Yet such rains reduce temperatures and can replenish groundwater tables and rivers.
During the post-monsoon or autumn months of October to December, a different monsoon cycle, the northeast (or "retreating") monsoon, brings dry, cool, and dense air masses to large parts of India. Winds spill across the Himalayas and flow to the southwest across the country, resulting in clear, sunny skies.[49] Though theIndia Meteorological Department (IMD) and other sources refers to this period as a fourth ("post-monsoon") season,[50][51][52] other sources designate only three seasons.[53] Depending on location, this period lasts from October to November, after the southwest monsoon has peaked. Less and less precipitation falls, and vegetation begins to dry out. In most parts of India, this period marks the transition from wet to dry seasonal conditions. Average daily maximum temperatures range between 25 and 34 °C (77 and 93 °F) in the Southern parts.
The northeast monsoon, which begins between September and October, lasts through the post-monsoon seasons, and only ends between December and January. It carries winds that have already lost their moisture out to the ocean (opposite from the summer monsoon). They cross India diagonally from northeast to southwest. However, the large indentation made by the Bay of Bengal into India's eastern coast means that the flows are humidified before reachingCape Comorin and rest of Tamil Nadu, meaning that the state, and also some parts of Kerala, experience significant precipitation in the post-monsoon and winter periods.[19] However, parts of West Bengal, Orissa, Andhra Pradesh,Karnataka and Mumbai also receive minor precipitation from the north-east monsoon.
Shown below are temperature and precipitation data for selected Indian cities; these represent the full variety of major Indian climate types. Figures have been grouped by the four-season classification scheme used by the Indian Meteorological Department;[N 1] year-round averages and totals are also displayed.
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Climate-related natural disasters cause massive losses of Indian life and property. Droughts, flash floods, cyclones, avalanches, landslides brought on by torrential rains, and snowstorms pose the greatest threats. Other dangers include frequent summer dust storms, which usually track from north to south; they cause extensive property damage in North India[59] and deposit large amounts of dust from arid regions. Hail is also common in parts of India, causing severe damage to standing crops such as rice and wheat.
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In the Lower Himalayas, landslides are common. The young age of the region's hills result inlabile rock formations, which are susceptible to slippages. Short duration high intensity rainfall events typically trigger small scale landslides while long duration low intensity rainfall periods tend to trigger large scale catastrophic landslides.[60] Rising population and development pressures, particularly from logging and tourism, cause deforestation. The result, denuded hillsides, exacerbates the severity of landslides, since tree cover impedes the downhill flow of water.[61] Parts of the Western Ghats also suffer from low-intensity landslides. Avalanches occur in Jammu and Kashmir, Himachal Pradesh, Uttarakhand, Sikkim and Arunachal Pradesh.
Floods are the most common natural disaster in India. The heavy southwest monsoon rains cause theBrahmaputra and other rivers to distend their banks, often flooding surrounding areas. Though they provide rice paddy farmers with a largely dependable source of natural irrigation and fertilisation, the floods can kill thousands and displace millions. Excess, erratic, or untimely monsoon rainfall may also wash away or otherwise ruin crops.[62] Almost all of India is flood-prone, and extreme precipitation events, such as flash floods and torrential rains, have become increasingly common in central India over the past several decades, coinciding with rising temperatures. Mean annual precipitation totals have remained steady due to the declining frequency of weather systems that generate moderate amounts of rain.[63]
Tropical cyclones, which are severe storms spun off from theIntertropical Convergence Zone, may affect thousands of Indians living in coastal regions.Tropical cyclogenesis is particularly common in the northern reaches of the Indian Ocean in and around the Bay of Bengal. Cyclones bring with them heavy rains,storm surges, and winds that often cut affected areas off from relief and supplies. In the North Indian Ocean Basin, the cyclone season runs from April to December, with peak activity between May and November.[64] Each year, an average of eight storms with sustained wind speeds greater than 63 km/h (39 mph) form; of these, two strengthen into true tropical cyclones, which sustain gusts greater than 117 km/h (73 mph). On average, a major (Category 3 or higher) cyclone develops every other year.[64][65]
During summer, theBay of Bengal is subject to intense heating, giving rise to humid and unstable air masses that morph into cyclones. The1737 Calcutta cyclone, the1970 Bhola cyclone, and the1991 Bangladesh cyclone rank among themost powerful cyclones to strike India, devastating the coasts of eastern India and neighbouring Bangladesh. Widespread death and property destruction are reported every year in the exposed coastal states of West Bengal, Orissa, Andhra Pradesh, and Tamil Nadu. India's western coast, bordering the more placid Arabian Sea, experiences cyclones only rarely; these mainly strike Gujarat and Maharashtra, less frequently in Kerala.
The1999 Odisha cyclone was the most intense tropical cyclone in this basin and also the most powerful tropical cyclone to make landfall in India. With peak winds of 260 kilometres per hour (162 mph), it was the equivalent of aCategory 5 hurricane.[66] Almost two million people were left homeless;[67]another 20 million people lives were disrupted by the cyclone.[67] Officially, 9,803 people died from the storm;[66] unofficial estimates place the death toll at over 10,000.[67]
Indian agriculture is heavily dependent on the monsoon as a source of water. In some parts of India, the failure of the monsoons results in water shortages, resulting in below-average crop yields. This is particularly true of major drought-prone regions such as southern and eastern Maharashtra, northern Karnataka, Andhra Pradesh, Western Orissa, Gujarat, and Rajasthan. In the past, droughts have periodically led tomajor Indian famines. These include theBengal famine of 1770, in which up to one third of the population in affected areas died; the 1876–1877 famine, in which over five million people died; the 1899 famine, in which over 4.5 million died; and theBengal famine of 1943, in which over five million died from starvation and famine-related illnesses.[68][69]
All such episodes of severe drought correlate withEl Niño-Southern Oscillation (ENSO) events.[70][71] El Niño-related droughts have also been implicated in periodic declines in Indian agricultural output.[72] Nevertheless, ENSO events that have coincided with abnormally high sea surfaces temperatures in the Indian Ocean—in one instance during 1997 and 1998 by up to 3 °C (5 °F)—have resulted in increased oceanic evaporation, resulting in unusually wet weather across India. Such anomalies have occurred during a sustained warm spell that began in the 1990s.[73] A contrasting phenomenon is that, instead of the usual high pressure air mass over the southern Indian Ocean, an ENSO-related oceanic low pressure convergence centre forms; it then continually pulls dry air from Central Asia, desiccating India during what should have been the humid summer monsoon season. This reversed air flow causes India's droughts.[74] The extent that an ENSO event raisessea surface temperatures in the central Pacific Ocean influences the extent of drought.[70]
A study from 2005 concluded that heat waves significantly increased in frequency, persistence and spatial coverage in the decade 1991–2000, when compared to the period between 1971–80 and 1981–90. A severe heat wave inOrissa in 1998 resulted in nearly 1300 deaths. Based on observations, heat wave related mortality has increased in India prior to 2005.[75] The2015 Indian heat wave killed more than 2,500 people. In April 2024, the India Meteorological Department (IMD) forecasted a heat wave spell lasting approximately ten to twenty days longer than normal length of four to eight days during the three-month period between April and June.[76] InJune 2024, day temperatures reached 44.9 °C (112.8 °F) inNew Delhi, which were at their highest in six years. Five people have been reported as dead due to this heatwave.[77][78]
India's lowest recorded temperature was −45.0 °C (−49 °F) inDras,Ladakh. However, temperatures onSiachen Glacier nearBilafond La (5,450 metres or 17,881 feet) andSia La (5,589 metres or 18,337 feet) have fallen below −55 °C (−67 °F),[79] while blizzards bring wind speeds in excess of 250 km/h (155 mph),[80] orhurricane-force winds ranking at 12—the maximum—on theBeaufort scale. These conditions, not hostile actions, caused more than 97% of the roughly 15,000 casualties suffered among Indian and Pakistani soldiers during theSiachen conflict.[79][80][81]
The highest temperature ever recorded in India occurred on 16 May 2016 inPhalodi, Rajasthan at 51.0 °C (124 °F). A temperature of up to 52.4 °C (126 °F) has been recorded in Jaisalmer District on 2 May 2016 near the border of Pakistan but the standard conditions are yet to be verified.
The average annual precipitation of 11,861 millimetres (467 in) in the village ofMawsynram, in the hilly northeastern state of Meghalaya, is the highest recorded in Asia, and possibly on Earth.[82] The village, which sits at an elevation of 1,401 metres (4,596 ft), benefits from its proximity to both the Himalayas and the Bay of Bengal. However, since the town ofCherrapunji, 5 kilometres (3.1 mi) to the east, is the nearest town to host a meteorological office—none has ever existed in Mawsynram—it is officially credited as being the world's wettest place.[83] In recent years the Cherrapunji-Mawsynram region has averaged between 9,296 and 10,820 millimetres (366 and 426 in)[9] of rain annually, though Cherrapunji has had at least one period of daily rainfall that lasted almost two years.[84] India's highest recorded one-day rainfall total occurred on 26 July 2005, when Mumbai received 944 mm (37 in);[85]the massive flooding that resulted killed over 900 people.[86][87]
Remote regions of Jammu and Kashmir, such as thePir Panjal Range, experience exceptionally heavy snowfall. Kashmir's highest recorded monthly snowfall occurred in February 1967, when 8.4 metres (27.6 ft) fell inGulmarg, though the IMD has recorded snowdrifts up to 12 metres (39.4 ft) in several Kashmiri districts. In February 2005, more than 200 people died when, in four days, a western disturbance brought up to 2 metres (6.6 ft) of snowfall to parts of the state.[88]
India was ranked seventh among the list of countries most affected byclimate change in 2019.[89] India emits about 3 gigatonnes (Gt)CO2eq ofgreenhouse gases each year; about two and a half tons per person, which is less than the world average.[90] The country emits 7% of global emissions, despite having 17% of the world population.[91] Theclimate change performance index of India ranks eighth among 63 countries which account for 92% of all GHG emissions in the year 2021.[92]
Temperature rises on theTibetan Plateau are causingHimalayan glaciers to retreat, threatening the flow rate of theGanges,Brahmaputra,Yamuna and other major rivers. A 2007World Wide Fund for Nature (WWF) report states that theIndus River may run dry for the same reason.[93] Severe landslides and floods are projected to become increasingly common in such states asAssam.[94]Heat waves' frequency and intensity are increasing in India because of climate change.[95] Temperatures in India have risen by 0.7 °C (1.3 °F) between 1901 and 2018.[96]
Thick haze and smoke originating from burning biomass in northwestern India[98] and air pollution from large industrial cities in northern India[99] often concentrate over theGanges Basin. Prevailing westerlies carry aerosols along the southern margins of the sheer-faced Tibetan Plateau towards eastern India and theBay of Bengal. Dust andblack carbon, which are blown towards higher altitudes by winds at the southern margins of the Himalayas, can absorb shortwave radiation and heat the air over the Tibetan Plateau. The net atmospheric heating due to aerosol absorption causes the air to warm andconvect upwards, increasing the concentration of moisture in the mid-troposphere and providing positive feedback that stimulates further heating of aerosols.[99]
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