Climate of Delhi

The climate of Delhi is an overlap between monsoon-influenced humid subtropical (Köppen climate classification Cwa) and semi-arid (Köppen climate classification BSh), with high variation between summer and winter temperatures and precipitation. Delhi's version of a humid subtropical climate is markedly different from many other humid subtropical cities such as Sao Paulo, New Orleans and Brisbane in that the city features dust storms (something more commonly seen in a desert climate) and wildfire haze (something seen in a tropical climate during the dry season) due to its semi-arid climate.[1]

New Delhi
Climate chart (explanation)
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Average max. and min. temperatures in °C
Precipitation totals in mm
Source: IMD

Summer starts in early April and peaks in late May or early June, with average temperatures near 38°C although occasional heat waves can result in highs close to 45°C (114°F) on some days and therefore higher apparent temperature. The monsoon starts in late June and lasts until mid-September, with about 797.3 mm (31.5 inches)[2] of rain. The average temperatures are around 29°C (85°F), although they can vary from around 25°C (78°F) on rainy days to 32°C (90°F) during dry spells. The monsoons recede in late September, and the post-monsoon season continues till late October, with average temperatures sliding from 29°C (85°F) to 21°C (71°F).

Winter starts in November and peaks in January, with average temperatures around 6–7°C. Although winters are cold, Delhi's proximity to the Himalayas results in cold waves leading to lower apparent temperature due to wind chill. Delhi is notorious for its heavy fogs and haze during the winter season. In December, reduced visibility leads to disruption of road, air and rail traffic.[3] Winter ends by the first week of March.

Extreme temperatures have ranged from −2.2°C to 48.4°C.[4]

Classifications
Delhi Climate according to major climate systems
Climatic scheme Initials Description
Köppen system[5]
Cwa
 Monsoon-influenced humid subtropical
Trewartha system[6]
Aw
 Tropical wet-and-dry
Alisov system[7] N/A Sub-equatorial climate
Strahler system[8] N/A Dry tropical semi-arid
Thornthwaite system[9]
DA'd
 Semi-arid and megathermal
Neef system[10] N/A Tropical alternating climate equatorial climate

Overview of Seasonal Distribution
  • Spring: February, March; Warm days, Cool nights, Pleasant; Low to moderate humidity; Moderate precipitation
  • Summer: April, May; Hot to very hot; Very low to moderate humidity; Low precipitation
  • Monsoon (Rainy): June, July, August, September; Hot, Pleasant during rains; High to very high humidity; Heavy precipitation
  • Autumn: October, November; Warm days, Cool nights, Pleasant; Low humidity; Low precipitation
  • Winter: December, January; Cool days, Cold nights; Moderate humidity; Medium precipitation

Seasons

Delhi lies in the landlocked Northern Plains of the Indian Subcontinent. Its climate is greatly influenced by its proximity to the Himalayas and the Thar Desert, causing it to experience both weather extremes. Delhi has 5 distinct seasons, viz. Spring, Summer, Rainy, Autumn and Winter.[11] Broadly speaking, Delhi has long and scorching summers- sub-divided into summer and monsoon seasons, short and cold winters, and two bouts of pleasant transition seasons. Two most important wind patterns influencing Delhi's climate are the Western Disturbance and the South-West Winds.

Spring

Around the middle of February, Delhi's climate sees another transition, this time from Winter to Summer. The transition weather is known as Spring and is characterized by warm days, cool nights, dry ambiance and lively natural surroundings.[12] The weather is pleasant and there is warm, brilliant sunshine during the day. Spring rains[13] are a characteristic of this season. These rains may be accompanied by hail and can be heavy. Average temperatures show a slow, gradual rise as the wind direction shift from North-West to South-West, thereby getting warmer. Around late spring/ early summer, the variation between morning and afternoon temperatures in a day becomes considerable, and can often be more than 20 °C, with maximum rising to mid 30s °C and minimum in the mid 10s °C. Spring ends by the latter half of March and the day temperatures exceed 30 °C by then,[14] marking the onset of the next summer.

Summer

Summer begins in early April and continues till the middle of June, with the heat peaking in late May/early June. It is characterized by extreme heat, low humidity, very hot winds and thunderstorms. Delhi's proximity to the Thar Desert results in hot, dry continental winds, called loo, at times blowing all across from the West Asian mainland, making the days feel hotter. These winds, blowing over from vast land stretches, are very hot and dry. Since the Western Disturbance depression moves eastward (and is the reason for cyclonic occurrences in Eastern Coastal areas) by this time of the year, there is no moisture-laden wind to increase humidity. The air therefore remains dry or very dry during day. For most of its summer season, Delhi has a semi-arid climate.[1] Coming from Spring, the city witnesses a spurt in day temperature around early April, whereas nights still remain pleasant. By the latter part of April or during early May, maximum temperatures exceed 40°C while the ambience remains very dry. Night temperatures cross the 20°C mark towards the latter part of April. May is Delhi's hottest month during which temperatures may reach 45°C or higher.[15] This month is characterized by frequent thunderstorms.[16] Dust storms are another feature of Delhi's summer,[17][18] and can be severe and destructive when accompanied by strong winds, particularly under cumulonimbus formation.[19] These are caused due to fine dust brought along by the hot winds arriving from the desert. They make the surroundings appear pale yellow, bring temperatures slightly down and are usually followed by thunderstorms. Post mid-June, temperatures start falling slowly, while humidity shows a gradual rise. A visual characteristic of summer in Delhi is the summer bloom, particularly the blooming Bougainvillea, Amaltas, Gulmohar, Shireesh and Jacaranda trees, which look spectacular when fully flowering during peak summer in May.[20]

Monsoon

Monsoon winds arrive in Delhi by either the end of June or the first week of July.[11] The arrival of moisture laden South-Western winds, traveling from the Arabian Sea marks the onset of the humid season in Delhi. This season is marked by high levels of humidity and high heat. Day temperatures drop below 40°C as humidity suddenly soars.[21] July is marked by high heat and relatively less precipitation (as compared to August). This transition from scorching to sweltering heat between June and July makes the latter feel very uncomfortable. August is Delhi's wettest month. The heat is considerably reduced and it is relatively cooler for most part of the month. There is dense cloud formation in the sky and at least a week of distinct, very heavy rainfall.[22] By September, the amount and frequency of precipitation drops, though humidity remains high.[23] Towards the end of September, moisture content in the air begins to fall and monsoon ends by early October.

Autumn

The end of monsoon marks the arrival of a transition season. Autumn arrives by early or mid October, and is marked by very dry ambiance, warm days and pleasant nights. Maximum temperatures drop below 30°C by late October and there is a gradual fall in average temperature. Minimum temperature drops below 20 °C.[24] During Autumn, the wind direction begins changing from South-Westerly to North-Westerly. Around late autumn/early winter, the variation between morning and afternoon temperatures in a day becomes considerable, and can often be more than 20°C, with minimum dropping to under 10°C and maximum still hovering slightly under 30°C. This season ends by early December.

Winter

Winter arrives in Delhi by early November. Minimum temperatures gradually enter single digits by this time of the year, while days are cool. Though usually not cold initially, December suddenly becomes cold in the latter half, as chilly north-western winds from the Himalayas begin sweeping the Northern Plains. These cold waves are caused by a depression created by Western Disturbance, which bring cloud cover and winter rains to the Plains, and add to snowfall in the North-Western Indian Subcontinent. By early January, when winter peaks in Delhi, the minimum temperatures plunge to the vicinity of 0 °C,[25] though very rarely entering the negative scale. Maximum temperatures, too may drop down into single digits[26] and always stay under 15°C. When the minimum temperature ventures very close to the 0 °C mark, Delhi witnesses frost.[27] Snow is a practical impossibility for Delhi (and the rest of Northern Plains) due to very dry nature of its winter- the coldest conditions happen under clear skies when icy winds rush in from the Himalayas, and a cloud cover (which is necessary for causing snowfall) rather warms the city by trapping heat, thereby junking any possibility of snow. Delhi's winter is marked by very dense fog and haze, which dramatically reduce visibility[28] and makes days colder by cutting off sunlight. In the opposite scenario, cold north-westerly winds from the upper reaches of Himalayas blowing across the city makes the days feel colder, despite any sunshine and the nights further cold.[29] Post mid-January, average temperatures begin to rise very gradually, though the rise is almost contained by the cold north-western winds which result due to very heavy snowfall that occurs in the Himalayas during this part of the month.[30] It may rain towards the end of January and the precipitation is usually accompanied by hail,[31] resulting in slight increase in minimum temperatures due to cloud cover. Maximum temperatures again cross 20 °C and days become pleasant. By mid-February or somewhat beyond, minimum temperatures cross the 10°C mark and days start getting warmer gradually, marking the end of winter. Delhi can sometimes have a prolonged season of chill, extending into March.[32][33]

Climate data

Temperature records for Delhi exist for a period of a little over 100 years. The lowest ever temperature reading during this period is -2.2  °C, recorded on 11 January 1967 at Met Delhi Palam. And, the highest ever temperature reading during the same period is 48.4 °C recorded on 26 May 1998, again at Met Delhi Palam.[4][34]

Climate data for New Delhi (Safdarjung) 1981–2010, extremes 1901–present
Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year
Record high °C (°F) 32.4
(90.3)		 34.1
(93.4)		 40.6
(105.1)		 45.6
(114.1)		 47.2
(117.0)		 46.7
(116.1)		 45.0
(113.0)		 42.0
(107.6)		 40.6
(105.1)		 39.4
(102.9)		 36.1
(97.0)		 30.0
(86.0)		 47.2
(117.0)
Mean maximum °C (°F) 25.5
(77.9)		 29.1
(84.4)		 35.3
(95.5)		 41.3
(106.3)		 43.7
(110.7)		 43.8
(110.8)		 39.7
(103.5)		 37.4
(99.3)		 37.1
(98.8)		 36.0
(96.8)		 32.2
(90.0)		 27.0
(80.6)		 44.5
(112.1)
Average high °C (°F) 20.5
(68.9)		 23.9
(75.0)		 29.6
(85.3)		 36.3
(97.3)		 39.5
(103.1)		 39.2
(102.6)		 35.4
(95.7)		 34.1
(93.4)		 34.1
(93.4)		 32.8
(91.0)		 28.2
(82.8)		 23.1
(73.6)		 31.4
(88.5)
Daily mean °C (°F) 14.1
(57.4)		 17.4
(63.3)		 22.7
(72.9)		 28.9
(84.0)		 32.7
(90.9)		 33.2
(91.8)		 31.4
(88.5)		 30.3
(86.5)		 29.6
(85.3)		 26.0
(78.8)		 20.5
(68.9)		 15.5
(59.9)		 25.2
(77.4)
Average low °C (°F) 7.6
(45.7)		 10.4
(50.7)		 15.6
(60.1)		 21.3
(70.3)		 25.8
(78.4)		 27.9
(82.2)		 27.4
(81.3)		 26.6
(79.9)		 25.0
(77.0)		 19.1
(66.4)		 12.9
(55.2)		 8.3
(46.9)		 19.0
(66.2)
Mean minimum °C (°F) 4.1
(39.4)		 6.1
(43.0)		 10.7
(51.3)		 16.0
(60.8)		 20.8
(69.4)		 22.3
(72.1)		 24.0
(75.2)		 23.6
(74.5)		 21.7
(71.1)		 14.7
(58.5)		 8.6
(47.5)		 4.6
(40.3)		 3.6
(38.5)
Record low °C (°F) −0.6
(30.9)		 1.6
(34.9)		 4.4
(39.9)		 10.7
(51.3)		 15.2
(59.4)		 18.0
(64.4)		 20.3
(68.5)		 20.7
(69.3)		 17.3
(63.1)		 9.4
(48.9)		 3.9
(39.0)		 0.0
(32.0)		 −0.6
(30.9)
Average rainfall mm (inches) 19.3
(0.76)		 22.1
(0.87)		 15.9
(0.63)		 13.0
(0.51)		 31.5
(1.24)		 82.2
(3.24)		 187.3
(7.37)		 232.5
(9.15)		 129.8
(5.11)		 14.3
(0.56)		 4.9
(0.19)		 9.4
(0.37)		 762.3
(30.01)
Average rainy days 1.3 1.8 1.6 1.2 2.5 4.6 9.4 9.8 5.5 1.0 0.5 0.9 40.1
Average relative humidity (%) (at 17:30 IST) 52 42 35 23 26 39 62 66 58 44 48 54 45
Mean monthly sunshine hours 220.1 223.2 248.0 276.0 285.2 219.0 179.8 176.7 219.0 260.4 246.0 220.1 2,773.5
Mean daily sunshine hours 7.1 7.9 8.0 9.2 9.2 7.3 5.8 5.7 7.3 8.4 8.2 7.1 7.6
Source 1: India Meteorological Department (sun 1971–2000)[35][36][37][38][39][40][41]
Source 2: Tokyo Climate Center (mean temperatures 1981–2010)[42]
Climate data for Delhi (Palam) 1981–2010, extremes 1956–present
Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year
Record high °C (°F) 31.0
(87.8)		 35.7
(96.3)		 41.3
(106.3)		 45.3
(113.5)		 48.4
(119.1)		 47.6
(117.7)		 45.7
(114.3)		 43.2
(109.8)		 40.8
(105.4)		 40.7
(105.3)		 36.4
(97.5)		 30.4
(86.7)		 48.4
(119.1)
Average high °C (°F) 20.4
(68.7)		 24.1
(75.4)		 29.9
(85.8)		 37.1
(98.8)		 40.3
(104.5)		 39.9
(103.8)		 35.9
(96.6)		 34.4
(93.9)		 34.7
(94.5)		 33.4
(92.1)		 28.5
(83.3)		 22.8
(73.0)		 31.8
(89.2)
Average low °C (°F) 7.3
(45.1)		 10.2
(50.4)		 15.1
(59.2)		 21.4
(70.5)		 26.0
(78.8)		 27.7
(81.9)		 27.0
(80.6)		 26.2
(79.2)		 24.7
(76.5)		 19.5
(67.1)		 13.6
(56.5)		 8.8
(47.8)		 19.0
(66.2)
Record low °C (°F) −2.2
(28.0)		 −1.6
(29.1)		 3.4
(38.1)		 8.6
(47.5)		 14.6
(58.3)		 19.8
(67.6)		 17.8
(64.0)		 20.2
(68.4)		 13.6
(56.5)		 9.9
(49.8)		 2.1
(35.8)		 −1.3
(29.7)		 −2.2
(28.0)
Average rainfall mm (inches) 18.4
(0.72)		 20.0
(0.79)		 13.2
(0.52)		 9.1
(0.36)		 37.7
(1.48)		 82.1
(3.23)		 174.4
(6.87)		 188.7
(7.43)		 105.3
(4.15)		 13.7
(0.54)		 5.1
(0.20)		 6.9
(0.27)		 674.5
(26.56)
Average rainy days 1.4 1.7 1.4 1.0 2.6 4.0 8.6 8.3 4.6 0.9 0.5 0.7 35.7
Average relative humidity (%) (at 17:30 IST) 53 44 34 23 26 40 61 66 56 41 42 52 45
Source: India Meteorological Department[43][44][45]

Weather monitoring stations

Delhi has two weather monitoring stations, one at Safdarjung inside the main city and other at Palam on its outskirts near the Airport. The readings at Safdarjung station are taken as those for the city, whereas the readings at Palam station are taken as those for the Airport.

Day-length variation

Located at 28°36′36″N latitude, Delhi lies in the sub-tropical belt of earth's North Temperate geographical region, a few latitudes north of the Tropic of Cancer. As such the rotation of earth has its effect on the city's day-length, which shortens during winters and lengthens during summers. Between the two solstices, Delhi's day-length changes by about 4 hours, offset by some 2 hours each at sunrise and sunset.[46][47]

References
  1. "Delhi Climate". Weather Spark.
  2. "Climatological Table". Indian Meteorological Department. Archived from the original on 21 May 2009. Retrieved 13 May 2009.
  3. "Fog continues to disrupt flights, trains". The Hindu. Chennai, India. 7 January 2006. Retrieved 16 May 2006.
  4. "Ever Recorded Highest Maximum Temperature, Lowest Minimum Temperature and 24 Hours Heaviest Rainfall up to 2010" (PDF). Indian Met Department, Pune. Archived from the original (PDF) on 21 May 2013.
  5. Chakraborty, Surya; Kant, Yogesh; Mitra, Debashis (22 November 2013). "Assessment of land surface temperature and heat fluxes over Delhi using remote sensing data". Journal of Environmental Management. 148: 143–152. doi:10.1016/j.jenvman.2013.11.034. PMID 24360191.
  6. "Trewartha Maps". Retrieved 30 November 2020.
  7. Eguchi, Takashi (1986). "Global Climatic Classification Based on Seasonal Distribution of Non-Precipitation Areas". Geographical Review of Japan. 59 (1): 43–54.
  8. "World Strahler Climate Map".
  9. Feddema, Johannes J. (January 2005). "A Revised Thornthwaite-Type Global Climate Classification". Physical Geography. 26 (6): 442–466. doi:10.2747/0272-3646.26.6.442. ISSN 0272-3646. S2CID 128745497.
  10. "The Climate of Lake Aral". Retrieved 30 November 2020.
  11. "Seasons of Delhi". Delhi Tourism. Retrieved 17 June 2018.
  12. "Weather in Delhi in February".
  13. "2013 had heaviest February rains in 70 years".
  14. "When it rains during the spring season, day temperatures hardly cross 24 degrees Celsius while nights remain relatively cold at about 13 degrees Celsius Spring can often have cold waves resulting in low temperatures dropping to about 9 degrees Celsius in early march Weather in Delhi in March".
  15. "Weather in May in Delhi".
  16. "NDTV news on Delhi's thunderstorm".
  17. "A news mentioning Dust Storm in Delhi".
  18. "The Tribune's news featuring Delhi's Dust Storm".
  19. "Strong dust storm in Delhi on May 30, 2014".
  20. "Amaltas bloom in Delhi during May".
  21. "Weather in July in Delhi".
  22. "Weather in August in Delhi".
  23. "Weather in September in Delhi".
  24. "Weather in Delhi in November".
  25. "Delhi shivers at 1.9 degrees Celsius". The Hindu. Chennai, India. 7 January 2013.
  27. "When Delhi woke up to 'snow' - The Times of India". The Times Of India. 9 January 2006.
  28. "An instance of dense fog in Delhi".
  29. "Cold wave forces schools shut in Delhi".
  30. "Cold wave, slight rise in temperature on January 20, 2011".
  31. "Hailstorm in Delhi".
  32. "Cool March weather surprises Delhi". The Hindu. Chennai, India. 10 March 2012.
  33. "Coldest April in 30 years".
  34. "Extremes for Delhi" (PDF). Indian Meteorological Department. Archived from the original (PDF) on 21 May 2013. Retrieved 21 January 2015.
  35. "Station: New Delhi (Safdarjang) Climatological Table 1981–2010" (PDF). Climatological Normals 1981–2010. India Meteorological Department. January 2015. pp. 555–556. Archived from the original (PDF) on 5 February 2020. Retrieved 6 February 2020.
  36. "Extremes of Temperature & Rainfall for Indian Stations (Up to 2012)" (PDF). India Meteorological Department. December 2016. p. M46. Archived from the original (PDF) on 5 February 2020. Retrieved 6 February 2020.
  37. "New Delhi (Safdarjang) Climatological Table 1981–2010". India Meteorological Department. Retrieved 6 February 2020.
  38. "Table 3 Monthly mean duration of Sun Shine (hours) at different locations in India" (PDF). Daily Normals of Global & Diffuse Radiation (1971–2000). India Meteorological Department. December 2016. p. M-3. Archived from the original (PDF) on 5 February 2020. Retrieved 7 February 2020.
  39. "NEW DELHI (SAFDARJUNG) EXTREME WEATHER EVENTS IN THE MONTH OF DECEMBER". Retrieved 29 December 2020.
  40. "NEW DELHI (SAFDARJUNG) EXTREME WEATHER EVENTS IN THE MONTH OF JANUARY". Retrieved 29 December 2020.
  41. "NEW DELHI (SAFDARJUNG) EXTREME WEATHER EVENTS IN THE MONTH OF JUNE". Retrieved 29 December 2020.
  42. "Normals Data: New Delhi/Safdarjung - India Latitude: 28.58°N Longitude: 77.20°E Height: 211 (m)". Japan Meteorological Agency. Archived from the original on 29 February 2020. Retrieved 29 February 2020.
  43. "Station: New Delhi Palam (A) Climatological Table 1981–2010" (PDF). Climatological Normals 1981–2010. India Meteorological Department. January 2015. pp. 553–554. Archived from the original (PDF) on 5 February 2020. Retrieved 5 February 2020.
  44. "Extremes of Temperature & Rainfall for Indian Stations (Up to 2012)" (PDF). India Meteorological Department. December 2016. p. M46. Archived from the original (PDF) on 5 February 2020. Retrieved 25 December 2020.
  45. "New Delhi (Palam) Climatological Table 1981–2010". India Meteorological Department. Retrieved 5 February 2020.
  46. "Delhi Day length around Summer Solstice". timeanddate.com.
  47. "Delhi Day length around Winter Solstice". timeanddate.com.
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