Climate of India
The climate of India includes a wide range of weather conditions, influenced by its vast geographic scale and varied topography. Based on the Köppen 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 northern Himalayan regions, varying with elevation.
The Indo-Gangetic Plains in the north experience a humid subtropical climate which become more temperate at higher altitudes, like the Sivalik Hills, or continental in some areas like Gulmarg. In contrast, much of the south and the east exhibit tropical climate conditions, which support lush rainforests in parts of these territories. Many regions have starkly different microclimates, 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, summer, monsoon or south-west monsoon and post-monsoon or north-east monsoon. Some parts of the country with subtropical, temperate or continental climates also experience spring and autumn.
India's geography and geology are climatically pivotal: the Thar Desert in the northwest and the Himalayas in the north work in tandem to create a culturally and economically important monsoonal regime. As Earth's highest and most massive mountain range, the Himalayas bar the influx of frigid katabatic winds from the icy Tibetan Plateau and northerly Central Asia. Most of North 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 in South India is generally warmer, and more humid due to its coastlines. However some hill stations in South India such as Ooty are well known for their cold climate.
Though the Tropic 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 to change in frequency and severity as a consequence of human-induced climate change. Ongoing and future vegetative changes, sea level rise and inundation of India's low-lying coastal areas are also attributed to global warming.
Paleoclimate
History
During the Triassic period of 251–199.6 Ma, the Indian subcontinent was the part of a vast supercontinent known as Pangaea. Despite its position within a high-latitude belt at 55–75° S—latitudes now occupied by parts of the Antarctic 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. India later merged into the southern supercontinent Gondwana, a process beginning some 550–500 Ma. During the Late Paleozoic, Gondwana extended from a point at or near the South Pole to near the equator, where the Indian craton was positioned, resulting in a mild climate favorable to hosting high-biomass ecosystems. 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. During the Mesozoic, the world, including India, was considerably warmer than today. With the coming of the Carboniferous, global cooling stoked extensive glaciation, which spread northwards from South Africa towards India; this cool period lasted well into the Permian.Tectonic movement by the Indian Plate caused it to pass over a geologic hotspot—the Réunion hotspot—now occupied by the volcanic island of Réunion. This resulted in a massive flood basalt event that laid down the Deccan Traps some 60–68 Ma, at the end of the Cretaceous period. This may have contributed to the global Cretaceous–Paleogene extinction event, which caused India to experience significantly reduced insolation. Elevated atmospheric levels of sulphur gases formed aerosols such as sulphur dioxide and sulphuric acid, similar to those found in the atmosphere of Venus; these precipitated as acid rain. Elevated carbon dioxide emissions also contributed to the greenhouse effect, causing warmer 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 the Laurasian landmass, were severe enough to cause the extinction of many endemic Indian forms. 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.
More recently, in the Holocene epoch, 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. Kashmir's erstwhile subtropical climate dramatically cooled 2.6–3.7 Ma and experienced prolonged cold spells starting 600,000 years ago.
Regions
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. The Himalayas, along with the Hindu 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 similar latitudes. 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. 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. Groupings are assigned codes according to the Köppen climate classification system.Tropical
A tropical rainy climate governs regions experiencing persistent warm or high temperatures, which normally do not fall below. India predominantly hosts two climatic subtypes that fall into this group: tropical monsoon climate and tropical savanna climate.The most humid is the tropical wet climate—also known as the tropical monsoon climate—that covers a strip of southwestern lowlands abutting the Malabar Coast, the Western Ghats, and southern Assam. India's two island territories, Lakshadweep and the Andaman 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 per year. 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 a tropical 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 arid rain shadow east of the Western Ghats. Winter and early summer are long and dry periods with temperatures averaging above. Summer is exceedingly hot; temperatures in low-lying areas may exceed during May, leading to heat waves that can each kill hundreds of Indians. The rainy season lasts from June to September; annual rainfall averages between across the region. Once the dry northeast monsoon begins in September, most significant precipitation in India falls on Tamil Nadu and Puducherry leaving other states comparatively dry.
The Ganges Delta lies mostly in the tropical wet climate zone: it receives between of rainfall each year in the western part, and 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, and average temperatures in April range from. July is on average the coldest and wettest month: over of rain falls on the delta.
Additionally, Nicobar Islands rain forests experience a Tropical rainforest climate.
Arid and Semi-Arid Regions
and semi-arid climate dominates regions where the rate of moisture loss through evapotranspiration exceeds that from precipitation;A semi-arid steppe climate predominates over a long stretch of land south of Tropic of Cancer and east of the Western Ghats and the Cardamom Hills. The region, which includes Karnataka, inland Tamil Nadu, western Andhra Pradesh, and central Maharashtra, gets between annually. It is drought-prone, as it tends to have less reliable rainfall due to sporadic lateness or failure of the southwest monsoon. Karnataka is divided into three zones—coastal, north interior and south interior. Of these, the coastal zone receives the most precipitation, averaging per annum, far in excess of the state average of. In contrast to norm, Agumbe in the Shivamogga district receives the second highest annual rainfall in India. North of the Krishna 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. The months between March and May are hot and dry; mean monthly temperatures hover around, with precipitation. Hence, without artificial irrigation, this region is not suitable for permanent agriculture.
Most of western Rajasthan experiences an arid climatic regime. Cloudbursts are responsible for virtually all of the region's annual precipitation, which totals less than. 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 continuous downdrafts and other factors. The summer months of May and June are exceptionally hot; mean monthly temperatures in the region hover around, with daily maxima occasionally topping. 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 during summer; this widens by several degrees during winter. There is a small desert area in the south near Adoni in Andhra Pradesh, the only desert in South India, experiencing maximum temperatures of in summers and in winters.
To the west, in Gujarat, diverse climate conditions prevail. The winters are mild, pleasant, and dry with average daytime temperatures around and nights around with virtually full sun and clear nights. Summers are hot and dry with daytime temperatures around and nights no lower than. 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 but humidity is very high; nights are around. Most of the rainfall occurs in this season, and the rain can cause severe floods. The sun is often occluded during the monsoon season.
East of the Thar Desert, the Southwest Punjab–West Haryana–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 and winter cold as low as. May and June are hottest; December and January are coldest. Rainfall is varied, with the Shivalik Hills region being the wettest and the Bagar 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 the Himalayan 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, but can reach in summer and fall to 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, it is very unreliable; like in much of the rest of India, the southwest monsoon accounts for most precipitation. Summer daily maxima are around. All t his results in a natural vegetation typically comprising short, coarse grasses.