Thursday, June 9, 2016
Climatic Regions of India
India has a large variation in climate from region to region, due to its vast size. India experiences climate from four major climate groups. These can be further subdivided into seven climatic types. For ecological regions, see Ecoregions of India, for Regions see List of regions of India.
Tropical wet (humid) climate group[edit]
The regions belonging to this group experience persistent high temperatures which normally do not go below 18 °C even in the coolest month.
- Tropical wet (dry,humid)
The west coastal lowlands, the Western Ghats, and southern parts of Assam have this climate type. It is characterised by high temperatures throughout the year, even in the hills. The rainfall here is seasonal, but heavy and is above 78 cm in a year. Most of the rain is received in the period from May to November, and is adequate for the growth of vegetation during the entire year. December to March are the dry months with very little rainfall. The heavy rain is responsible for the tropical wet forests in these regions, which consists of a large number of species of animals.Evergreen forests are the typical feature of the region.
- Tropical wet and dry or savannah climate
Most of the plateau of peninsula India enjoys this climate, except a semi-arid tract to the east of the Western Ghats. Winter and early summer are long dry periods with temperature above 18 °C. Summer is very hot and the temperatures in the interior low level areas can go above 45 °C during May. The rainy season is from June to September and the annual rainfall is between 75 and 150 cm. Only central eastern Tamil Nadufalls under this tract and receives rainfall during the winter months of late November to January.
Dry climate group[edit]
This group consists of regions where the rate of evaporation of water is higher than the rate of moisture received through precipitation.
- Tropical semi-arid (steppe) climate
A long stretch of land situated to the south of Tropic of Cancer and east of the western ghats and the Cardamom Hills experiences this climate. It includesKarnataka, interior and western Tamil Nadu, western Andhra Pradesh and central Maharashtra.This area receives minimal rainfall due to being situated in the rainshadow area. This region is a famine prone zone with very unreliable rainfall which varies between 40 to 75 cm annually. Towards the north of Krishna River the summer monsoon is responsible for most of the rainfall, while to the south of the river rainfall also occurs in the months of October and November. The coldest month is December but even in this month the temperature remains between 20 °C and 24 °C. The months of March to May are hot and dry with mean monthly temperatures of around 32 °C. The vegetation mostly comprises grasses with a few scattered trees due to the rainfall. Hence this area is not very well suited for permanent agriculture.
- Sub-tropical arid (desert) climate
Most of western Rajasthan falls under this climate type characterised by scanty rainfall. Cloud bursts are largely responsible for the all the rainfall seen in this region which is less than 30 cm. These happen when the monsoon winds penetrate this region in the months of July, August and September. The rainfall is very erratic and a few regions might not see rainfall for a couple of years. The summer months of May and June are very hot with mean monthly temperatures in the region of 35 °C and highs which can sometimes reach 50 °C. During winters the temperatures can drop below freezing in some areas due to cold wave. There is a large diurnal range of about 14 °C during summer which becomes higher by a few more degrees during winter. This extreme climate makes this a sparsely populated region of India.
- Sub-tropical semi-arid (steppe) climate
The region towards the east of the tropical desert running from Punjab andHaryana to Kathiawar experiences this climate type. India's capital city Delhi lies in this climatic zone. This climate is a transitional climate falling between tropical desert and humid sub-tropical, with temperatures which are less extreme than the desert climate. The annual rainfall is between 30 to 65 cm but is very unreliable and happens mostly during the summer monsoon season. Maximum temperatures during summer can rise to 45 °C. Minimums during winter can drop down to freezing point. Areas under this belt do not experience high humidity throughout the year except during the monsoon season, and are generally dry. The vegetation mostly comprises short coarse grass. Some crops like jowar and bajra are also cultivated.
Sub-tropical humid climate group[edit]
The temperature during the coldest months in regions experiencing this climate falls between 18 and 0 °C.
- Sub-tropical humid (wet) with dry winters
The foothills of the Himalayas, Punjab-Haryana plain adjacent to the Himalayas, Rajasthan east of the Aravalli range, Uttar Pradesh, Bihar and northern part of West Bengal and Assam experience this climate. The rainfall is received mostly in the summer and is about 65 cm in the west and increases to 250 cm annually to the east and near the Himalayas. The winters are mainly dry due to the land derived winter winds which blow down the lowlands of north India towards the Bay of Bengal. The summers are hot and temperatures can reach 46 °C in the lowlands. May and June are the hottest months. Winter months are mostly dry with feeble winds. Frost occurs for a few weeks in winter. The difference in rainfall between the east and the west gives rise to a wide difference in the natural vegetation.
- Mountain climate or highland climate or alpine climate
In the Himalayan mountains the temperature falls by 0.6 °C for every 100 m rise in altitude and this gives rise to a variety of climates from nearly tropical in the foothills to tundra type above the snow line. One can also observe sharp contrast between temperatures of the sunny and shady slopes, high diurnal range of temperature, inversion of temperature, and variability of rainfall based on altitude.
The northern side of the western Himalayas also known as the trans-Himalayan belt is arid, cold and generally wind swept. The vegetation is sparse and stunted as rainfall is scanty and the winters are severely cold. Most of the snowfall is in the form of snow during late winter and spring months. The area to the south of the Himalayan range is protected from cold winds coming from interior of Asia during winter. The leeward side of the mountains receive less rain while the well exposed slopes get heavy rainfall. The places situated between 1070 and 2290 m altitudes receive the heaviest rainfall and the rainfall decreases rapidly above 2290m. The great Himalayan range witnesses heavy snowfall during winter months of December to February at altitudes above 1500m. The diurnal range of temperature is also high.
The states of Jammu and Kashmir, Himachal Pradesh, Uttarakhand, Arunachal Pradesh and Sikkim experience this kind of weather.
DisasterS
Disasters[edit]
Main article: Natural disasters in India
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[54] 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.
Floods and landslides[edit]
In the Lower Himalaya, landslides are common. The young age of the region's hills result inlabile rock formations, which are susceptible to slippages. 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.[55] Parts of the Western Ghats also suffer from low-intensity landslides. Avalanches occur in Kashmir, Himachal Pradesh, and Sikkim.
Floods are the most common natural disaster in India. The heavy southwest monsoon rains cause the Brahmaputra 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.[56] 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.[57]
Cyclones[edit]
See also: Cyclone Nilam
Tropical cyclones, which are severe storms spun off from the Intertropical 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.[58] 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 have sustained gusts greater than 117 km/h (73 mph). On average, a major (Category 3 or higher) cyclone develops every other year.[58][59]
During summer, the Bay of Bengal is subject to intense heating, giving rise to humid and unstable air masses that morph into cyclones. The 1737 Calcutta cyclone, the 1970 Bhola cyclone, and the 1991 Bangladesh cyclone rank among the most 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, less frequently, Kerala.
Cyclone 05B, a supercyclone that struck Orissa on 29 October 1999, was the deadliest in more than a quarter-century. With peak winds of 160 miles per hour (257 km/h), it was the equivalent of a Category 5 hurricane.[60] Almost two million people were left homeless;[61]another 20 million people lives were disrupted by the cyclone.[61] Officially, 9,803 people died from the storm;[60] unofficial estimates place the death toll at over 10,000.[61]
Droughts[edit]
Main article: Drought in India
Indian agriculture is heavily dependent on the monsoon as a source of water. In some parts of India, the failure of the monsoons result 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 to major Indian famines. These include the Bengal 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.[62][63]
All such episodes of severe drought correlate with El Niño-Southern Oscillation (ENSO) events.[64][65] El Niño-related droughts have also been implicated in periodic declines in Indian agricultural output.[66] 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.[67] 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.[68] The extent that an ENSO event raises sea surface temperatures in the central Pacific Ocean influences the extent of drought.[64]
Heat waves[edit]
A study from 2005 concluded that heat waves significantly increased in the 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 in Orissa in 1998, resulted in nearly 1300 deaths. Based on observations, heat wave related mortality has increased in India prior to 2005.[69] The 2015 Indian heat wave killed more than 2,500 people.
Extremes[edit]
Extreme Temperatures: Low[edit]
India's lowest recorded temperature was −45 °C (−49 °F) in Dras, Ladakh, in eastern Jammu and Kashmir; the reading was taken with non-standard equipment. Figures as low as −30.6 °C (−23 °F) have been taken in Leh, further east in Ladakh. However, temperatures on the disputed but Indian-controlled Siachen Glacier nearBilafond La (5,450 metres or 17,881 feet) and Sia La (5,589 metres or 18,337 feet) have fallen below −55 °C (−67 °F),[70] while blizzards bring wind speeds in excess of 250 km/h (155 mph),[71] or hurricane-force winds ranking at 12—the maximum—on the Beaufort scale. These conditions, not hostile actions, caused more than 97% of the roughly 15,000 casualties suffered among Indian and Pakistani soldiers during the Siachen conflict.[70][71][72]
Extreme Temperatures: High[edit]
The highest temperature ever recorded in India occurred on 19 May 2016 in Phalodi, Jodhpur District, Rajasthan at 51.0 °C (123.8 °F).[73] Before this, the highest reliable temperature reading was 50.6 °C (123.1 °F) in Alwar, Rajasthan in 1955. The India Meteorological Department doubts the validity of 55 °C (131 °F) readings reported in Orissa during 2005.[74]
Rain[edit]
The average annual precipitation of 11,872 millimetres (467 in) in the village of Mawsynram, in the hilly northeastern state of Meghalaya, is the highest recorded in Asia, and possibly on Earth.[75] 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 of Cherrapunji, 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.[76] In recent years the Cherrapunji-Mawsynram region has averaged between 9,296 and 10,820 millimetres (366 and 426 in)[10] of rain annually, though Cherrapunji has had at least one period of daily rainfall that lasted almost two years.[77] India's highest recorded one-day rainfall total occurred on 26 July 2005, when Mumbai received more than 650 mm (26 in);[78] the massive flooding that resulted killed over 900 people.[79][80]
Snowfall[edit]
Remote regions of Jammu and Kashmir such as Baramulla district in the east and the Pir Panjal Range in the southeast experience exceptionally heavy snowfall. In southern areas around Jammu the climate is typically monsoonal, though the region is sufficiently far west to average 40–100 mm (2–4 in) of rain monthly from January and March. In the hot season, Jammu city is very hot and can reach up to 40 °C (104 °F) while in July and August, very heavy—though erratic—rainfall occurs with monthly extremes of up to 650 millimetres (26 in). Rainfall declines in September; by October conditions are extremely dry, with temperatures of around 29 °C (84 °F). Across from the Pir Panjal range, the South Asian monsoon is no longer a factor and most precipitation falls in the spring from southwestern cloudbands. Because of its closeness to the Arabian Sea, Srinagar receives as much as 25 inches (635 mm) of rain from this source, with the wettest months being March to May with around 85 mm (3.3 inches) per month.
Leh and the Zanskars[edit]
North of the main Himalaya Range, even the southwestern cloudbands break up or founder; hence the climate of Leh and the Zanskars is extremely dry and cold. Annual precipitation is only around 100 mm (4 inches) per year and humidity is very low. This region is almost entirely above 3,000 metres (9,750 ft) above sea level; thus winters are extremely cold. In the Zanskars, the average January temperature is −20 °C (−4 °F) with extremes as low as −40 °C (−40 °F). All rivers freeze over; locals cross unbridged rivers in winter because summer glacier melt deepens the waters and inhibits fording. Summer in Leh and the Zanskars are a pleasantly warm 20 °C (68 °F), but the low humidity and thin air can render nights cold. Kashmir's highest recorded monthly snowfall occurred in February 1967, when 8.4 metres (27.6 ft) fell in Gulmarg, 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.[81]
Global warming[edit]
Main article: Effects of global warming on South Asia
See also: 2007 South Asian heat wave
Current sea level rise, increased cyclonic activity, increased ambient temperatures, and increasingly fickle precipitation patterns are effects of global warming that have affected or are projected to impact India. Thousands of people have been displaced by ongoing sea level rises that have submerged low-lying islands in the Sundarbans.[82] Temperature rises on the Tibetan Plateau are causing Himalayan glaciers to retreat, threatening the flow rate of the Ganges, Brahmaputra, Yamuna, and other major rivers; the livelihoods of hundreds of thousands of farmers depend on these rivers.[83] A 2007 World Wide Fund for Nature (WWF) report states that the Indus River may run dry for the same reason.[84]
Severe landslides and floods are projected to become increasingly common in such states as Assam.[85]Ecological disasters, such as a 1998 coral bleaching event that killed off more than 70% of corals in the reef ecosystems off Lakshadweep and the Andamans and was brought on by elevated ocean temperatures tied to global warming, are also projected to become increasingly common.[86][87][88] Meghalaya and other northeastern states are also concerned that rising sea levels will submerge much of Bangladesh and spawn a refugee crisis. If severe climate changes occurs, Bangladesh and parts of India that border it may lose vast tracts of coastal land.[89]
The Indira Gandhi Institute of Development Research has reported that, if the predictions relating to global warming made by theIntergovernmental Panel on Climate Change come to fruition, climate-related factors could cause India's GDP to decline by up to 9%. Contributing to this would be shifting growing seasons for major crops such as rice, production of which could fall by 40%. Around seven million people are projected to be displaced due to, among other factors, submersion of parts of Mumbai and Chennai if global temperatures were to rise by a mere 2 °C (3.6 °F).[90] Such shifts are not new. Earlier in the Holocene 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.[91] Kashmir's erstwhile subtropical climate dramatically cooled 2.6–3.7 Ma and experienced prolonged cold spells starting 600,000 years ago.[92]
Atmospheric pollution[edit]
Thick haze and smoke originating from burning biomass in northwestern India[93] and air pollution from large industrial cities in northern India[94] often concentrate over the Ganges Basin. Prevailing westerlies carry aerosols along the southern margins of the sheer-faced Tibetan Plateau towards eastern India and the Bay of Bengal. Dust and black 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 and convect upwards, increasing the concentration of moisture in the mid-troposphere and providing positive feedback that stimulates further heating of aerosols.[94]
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