Indian Climatic Regions & Seasons

Seasons of India

Winters

Winter is the season between autumn and spring. By the end of monsoons the temperature falls and it is the coldest season of the year. Meteorological winter is the season that witnesses shortest days and lowest average temperatures. The year’s coldest months are December and January. In winters temperatures average around 10–15 °C (50–59 °F) in the northwest; temperatures rise as one proceeds towards the equator, peaking around 20–25 °C (68–77 °F) in mainland India's southeast.

A common phenomenon during winters is “Western Disturbances” that causes rains in winters. The main cause behind Western Disturbances is the prevailing of low pressure near Mediterranean Sea. These winds then move towards India. These winds cause heavy precipitation towards the Southern Himalayas especially in the states of Jammu & Kashmir, Uttarakhand, Himachal Pradesh. Also, the two Himalayan states of Assam and Sikkim also witness heavy snowfall.  

Summers

During summers the temperature increases due to Sun’s vertical rays directly reaching Tropic of Cancer. Entire India witnesses summers from March to June, while the Northern India experiences it from April to July. April is the hottest month in most of Southern and Central India while it’s May for Northern India.

Norwesters (Pre monsoon Sqaull line thunderstorms) lead to hailstones being dropped during this season. By May, most of the Indian interior experiences mean temperatures over 32 °C (90 °F), while maximum temperatures often exceed 40 °C (104 °F). While entire India has higher temperatures, the higher altitudes or Hill Stations offer relief from heat due to their as they have comparatively lower temperatures.

Monsoons

Monsoon winds are strong and violent that often changes their direction with season. These winds always flow from colder regions to hotter regions. Monsoons blow from the land toward the sea in winter and from the sea toward land in the summer. The rainfall in India is a result of the South West trade winds that originate from High Pressure areas.

The South west monsoon winds arrive in two branches, namely the Bay of Bengal Branch and Arabian Sea Branch. The Arabian Sea Branch is three times stronger than the bay of Bengal Branch. The monsoon typically breaks over Indian Territory by around 25 May, when it lashes the Andaman and Nicobar Islands in the Bay of Bengal. It strikes the Indian mainland around 1 June near the Malabar Coast of Kerala. By June, it reaches Mumbai; it appears over Delhi by 29 June.

The Bay of Bengal branch, which initially tracks the Coromandal Coast northeast from Cape Comorin to Orissa, swerves to the northwest towards the Indo-Gangetic Plain. The Arabian Sea branch moves northeast towards the Himalayas. By the first week of July, the entire country experiences monsoon rain.

Post-Monsoons

The months from October to December come under the Post-Monsoon season. During these months there is a different monsoon cycle called the North-east monsoon brings dry and cool air masses to India. As South west monsoons begin to decrease, climate begins to be drier and the precipitation also decreases. The North East monsoons carry winds that have already lost their moisture while traveling across Central Asia.

However, the states of Tamil Nadu and Kerala receive good precipitation during the season. parts of West Bengal, Orissa, Andhra Pradesh, Karnataka and North-East India also receive minor precipitation from the northeast monsoon.

 Climatic Regions

 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. 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 southwest summer monsoon winds that, between June and October, provide the majority of India's rainfall.  Four major climatic groupings predominate, into which fall seven climatic zones that, as designated by experts, are defined on the basis of such traits as temperature and precipitation.

Tropical wet

A tropical rainy climate governs regions experiencing persistent warm or high temperatures, which normally do not fall below 18 °C  . India hosts two climatic subtypes that fall under this group. The most humid is the tropical wet climate—also known as a 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 200 cm   per year.  Most rainfall occurs between May and November; this moisture is enough to sustain lush forests 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 exceptionally biodiverse tropical wet forests in parts of these regions.   Winter and early summer are long and dry periods with temperatures averaging above18 °C. Summer is exceedingly hot; temperatures in low-lying areas may exceed 50 °C   during May.  

The rainy season lasts from June to September; annual rainfall averages between 75 – 150 cm  across the region. Once the dry northeast monsoon begins in September, most precipitation in India falls on Tamil Nadu, leaving other states comparatively dry. The state's normal annual rainfall is about 945 mm   of which 48% is delivered by the northeast monsoon and 32% by the southwest monsoon. Since the state is entirely dependent on rains for recharging its water resources, monsoon failures lead to acute water scarcity and severe drought. Tamil Nadu is classified into seven agro-climatic zones: northeast, northwest, west, southern, high rainfall, high altitude hilly, and the Kaveri delta, the last being the most fertile agricultural zone.  . The Ganges Delta lies mostly in the tropical wet climate zone: it receives between 150 cm to 200 cm   of rainfall each year in the western part, and 200 cm to 300 cm in the eastern part. The coolest month of the year, on average, is January; April and May are the warmest months.

Tropical dry

A tropical arid and semi-arid climate dominates regions where the rate of moisture loss through evapotranspiration exceeds that from precipitation; it is subdivided into three climatic subtypes. The first, a tropical 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 40–75 cm  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 heaviest rainfall with an average rainfall of about 350 cm  per annum, far in excess of the state average of 110 cm.  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 20–24 °C. The months between March to May are hot and dry; mean monthly temperatures hover around 32 °C, with 320 millimetres  precipitation. Hence, without artificial irrigation, this region is not suitable for permanent agriculture.

Most of western Rajasthan experiences an arid climatic regime.  The summer months of May and June are exceptionally hot; mean monthly temperatures in the region over around 35 °C, 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 14 °C during summer; this widens by several degrees during winter. To the west, in Gujarat, diverse climate conditions obtain.  

East of the Thar Desert, the Punjab-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 50 °C and winter cold as low as 1 °C. May and June are hottest; December and January are coldest. Rainfall is varied, with the Shivalik Hills region being the wettest and the Aravali Hills region being the driest. About 80% 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 spans from mid-April to the end of June. Temperatures typically range from–2 °C to 40 °C, but can reach 47 °C  in summer and −4 °C in winter.  Daily summer temperature maxima rise to around 40 °C; this results in natural vegetation typically comprises short, coarse grasses.

Subtropical humid

Most of Northeast India and much of North India are subject to a humid subtropical climate. Though they experience hot summers, temperatures during the coldest months may fall as low as0 °C.  In most of this region, there is very little precipitation during the winter, owing to powerful anticyclonic and katabatic (downward-flowing) winds from Central Asia.

Humid subtropical regions are subject to pronounced dry winters. Winter rainfall—and occasionally snowfall—is associated with large storm systems such as "Nor'westers" and "Western disturbances"; the latter are steered by westerlies towards the Himalayas. Most summer rainfall occurs during powerful thunderstorms associated with the southwest summer monsoon; occasional tropical cyclones also contribute. Annual rainfall ranges from less than 100 cm in the west to over 250 cm  in parts of the northeast. As most of this region is far from the ocean, the wide temperature swings more characteristic of a continental climate predominate; the swings are wider than in those in tropical wet regions, ranging from 24 °C in north-central India to 27 °C  in the east.

Mountain

India's northernmost areas are subject to a montane, or alpine, climate.  In terms of environmental lapse rate, ambient temperatures fall by 6.5 °C  for every 1,000 metres  rise in altitude. Thus, climates ranging from nearly tropical in the foothills to tundra above the snow 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, is a region of barren, arid, frigid, and wind-blown wastelands. Most precipitation occurs as snowfall during the late winter and spring months.

Areas south of the Himalayas are largely protected from cold winter winds coming in from the Asian interior. The leeward side   of the mountains receives less rain while the southern slopes, well-exposed to the monsoon, get heavy rainfall. Areas situated at elevations of 1,070–2,290 metres  receive the heaviest rainfall, which decreases rapidly at elevations above 2,290 metres. The Himalayas experience their heaviest snowfall between December and February and at elevations above 1,500 metres. Snowfall increases with elevation by up to several dozen millimetres per 100 metre  increase. Elevations above 5,000 metres  never experience rain; all precipitation falls as snow.