Kolkata-II – Geograohy, climate and urban structure

Geography

Main article: Geography of Kolkata

Kolkata Skyline
Spread roughly north–south along the east bank of the Hooghly River, Kolkata sits within the lower Ganges Delta of eastern India; the city’s elevation is 1.5–9 m (5–30 ft).[49] Much of the city was originally a wetland that was reclaimed over the decades to accommodate a burgeoning population.[50] The remaining undeveloped areas, known as the East Kolkata Wetlands, were designated a “wetland of international importance” by theRamsar Convention (1975).[51] As with most of the Indo-Gangetic Plain, the soil and water are predominantly alluvial in origin. Kolkata is located over the “Bengal basin”, a pericratonic tertiary basin.[52] Bengal basin comprises three structural unit: shelf or platform in the west; central hinge or shelf/slope break; and deep basinal part in the east and southeast. Kolkata is located atop the western part of the hinge zone which is about 25 km (16 mi) wide at a depth of about 45,000 m (148,000 ft) below the surface.[52] The shelf and hinge zones have many faults, among them some are active. Total thickness of sediment below Kolkata is nearly 7,500 m (24,600 ft) above the crystalline basement; of these the top 350–450 m (1,150–1,480 ft) isquaternary, followed by 4,500–5,500 m (14,760–18,040 ft) of tertiary sediments, 500–700 m (1,640–2,300 ft) trap wash ofcretaceous trap and 600–800 m (1,970–2,620 ft) permiancarboniferous Gondwanarocks.[52] The quaternary sediments consist of clay, silt, and several grades of sand and gravel. These sediments are sandwiched between two clay beds: the lower one at a depth of 250–650 m (820–2,130 ft); the upper one 10–40 m (30–130 ft) in thickness.[53]According to the Bureau of Indian Standards, on a scale ranging from I to V in order of increasing susceptibility to earthquakes, the city lies inside seismic zone III;[54] according to a United Nations Development Programmereport, its wind and cyclone zone is “very high damage risk”.[54]

Urban structure

The Kolkata metropolitan area is spread over 1,886.67 km2 (728.45 sq mi)[55]:7 and comprises 3 municipal corporations (including Kolkata Municipal Corporation), 39 local municipalities and 24 panchayat samitis, as of 2011.[55]:7 The urban agglomeration encompassed 72 cities and 527 towns and villages, as of 2006.[56]Suburban areas in the Kolkata metropolitan area incorporate parts of the following districts: North 24 ParganasSouth 24 ParganasHowrah, Hooghly, and Nadia.[57]:15Kolkata, which is under the jurisdiction of theKolkata Municipal Corporation ( KMC), has an area of 185 km2 (71 sq mi).[56] The east–west dimension of the city is comparatively narrow, stretching from the Hooghly River in the west to roughly the Eastern Metropolitan Bypass in the east—a span of 9–10 km (5.6–6.2 mi).[58] The north–south distance is greater, and its axis is used to section the city into North, Central, and South Kolkata.

Kolkata skyline from Chowringhee

Howrah Bridge links Kolkata to Western bank of Ganges

Vidyasagar Setu – River Hooghly
North Kolkata is the oldest part of the city. Characterised by 19th-century architecture and narrow alleyways, it includes areas such as ShyambazarShobhabazarChitpur,CossiporeSinthee, and Dum Dum.[59]:65–66The north sub urban areas like Baranagar,BelghoriaSodepurKhardah up to Barrackpurare also within the city of Kolkata (as a metropolitan structure).
Central Kolkata hosts the central business district. It contains B. B. D. Bagh, formerly known as Dalhousie Square, and theEsplanade on its east; Strand Road is on its west.[60] The West Bengal SecretariatGeneral Post OfficeReserve Bank of IndiaHigh CourtLalbazar Police Headquarters, and several other government and private offices are located there. Another business hub is the area south of Park Street, which comprises thoroughfares such as Jawaharlal Nehru RoadCamac Street, Wood Street, Loudon Street, Shakespeare Sarani, and A. J. C. Bose Road.[61] The Maidan is a large open field in the heart of the city that has been called the “lungs of Kolkata”[62] and accommodates sporting events and public meetings.[63] TheVictoria Memorial and Kolkata Race Courseare located at the southern end of the Maidan. Among the other parks are Central Park in Bidhannagar and Millennium Park on Strand Road, along the Hooghly River.
South Kolkata developed after India gained independence in 1947; it includes upscale neighbourhoods such as BallygungeAlipore,New AliporeLansdowneBhowanipore,TollygungeJodhpur Park, Lake Gardens, Golf GreenJadavpur, and Kasba.[14] From south-west to south-east, outlying areas include Garden Reach, Behala, Thakurpukur, Kudghat,RanikuthiBansdroniBaghajatin, and Garia, along with the south sub urban areas like Narendrapur, Sonarpur, Baruipur, is within the city of Kolkata (as metropolitan structure). Two planned townships in the greater Kolkata region are Bidhannagar, also known as Salt Lake City and located north-east of the city; and Rajarhat, also called New Town and sited east of Bidhannagar.[14][64] In the 2000s, Sector V in Bidhannagar developed into a business hub for information technology and telecommunication companies.[65][66] Both Bidhannagar and New Town are situated outside the Kolkata Municipal Corporation limits, in their own municipalities.[64] Fort William, on the western part of the city, houses the headquarters of the Eastern Command of the Indian Army;[67] its premises are under the jurisdiction of the army.

Climate

Main article: Climate of Kolkata
Dark storm clouds over a waterbody with buildings in the far background

Monsoon clouds over Nalban, a part of East Kolkata Wetlands
Kolkata is subject to a tropical wet-and-dry climate that is designated Aw under theKöppen climate classification. The annual mean temperature is 26.8 °C (80.2 °F); monthly mean temperatures are 19–30 °C (66–86 °F).[68] Summers (March–June) are hot and humid, with temperatures in the low 30s Celsius; during dry spells, maximum temperatures often exceed 40 °C (104 °F) in May and June.[68] Winter lasts for only about two-and-a-half months, with seasonal lows dipping to 9–11 °C (48–52 °F) in December and January. May is the hottest month, with daily temperatures ranging from 27–37 °C (81–99 °F); January, the coldest month, has temperatures varying from 12–23 °C (54–73 °F). The highest recorded temperature is 43.9 °C (111.0 °F), and the lowest is 5 °C (41 °F).[68] Often, in April–June, the city is struck by heavy rains or dusty squalls followed by thunderstorms or hailstorms, bringing cooling relief from the prevailing humidity. These thunderstorms areconvective in nature, and are known locally askal bôishakhi (কালবৈশাখী), or “Nor’westers” in English.[69]
Rains brought by the Bay of Bengal branch of the south-west summer monsoon[70] lash Kolkata between June and September, supplying it with most of its annual rainfall of 1,582 mm (62 in). The highest monthly rainfall total, 306 mm (12 in), occurs in August. The city receives 2,528 hours of sunshine per year, with maximum sunlight exposure occurring in March.[71] Kolkata has been hit by several cyclones; these include systems occurring in 1737 and 1864 that killed thousands.[72][73]
Pollution is a major concern in Kolkata. As of 2008, sulphur dioxide and nitrogen dioxideannual concentration were within the national ambient air quality standards of India, but respirable suspended particulate matterlevels were high, and on an increasing trend for five consecutive years, causing smog and haze.[74][75] Severe air pollution in the city has caused a rise in pollution-related respiratory ailments, such as lung cancer.[76]
Climate data for Kolkata (Alipore) 1971–1990
Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year
Record high °C (°F) 32.8
(91)
38.4
(101.1)
41.1
(106)
43.3
(109.9)
43.7
(110.7)
43.9
(111)
39.9
(103.8)
38.4
(101.1)
38.9
(102)
39.0
(102.2)
34.9
(94.8)
32.5
(90.5)
43.9
(111)
Average high °C (°F) 26.4
(79.5)
29.1
(84.4)
33.5
(92.3)
35.3
(95.5)
35.4
(95.7)
34.0
(93.2)
32.3
(90.1)
32.1
(89.8)
32.4
(90.3)
32.3
(90.1)
30.3
(86.5)
27.0
(80.6)
31.7
(89.1)
Daily mean °C (°F) 20.1
(68.2)
23.0
(73.4)
27.6
(81.7)
30.2
(86.4)
30.7
(87.3)
30.3
(86.5)
29.2
(84.6)
29.1
(84.4)
29.1
(84.4)
28.2
(82.8)
24.9
(76.8)
20.8
(69.4)
26.9
(80.4)
Average low °C (°F) 13.8
(56.8)
16.9
(62.4)
21.7
(71.1)
25.1
(77.2)
26.0
(78.8)
26.5
(79.7)
26.1
(79)
26.1
(79)
25.8
(78.4)
23.9
(75)
19.6
(67.3)
14.5
(58.1)
22.2
(72)
Record low °C (°F) 6.7
(44.1)
7.2
(45)
10.0
(50)
16.1
(61)
17.9
(64.2)
20.4
(68.7)
20.6
(69.1)
22.6
(72.7)
20.6
(69.1)
17.2
(63)
10.6
(51.1)
7.2
(45)
6.7
(44.1)
Average rainfall mm (inches) 11
(0.43)
30
(1.18)
35
(1.38)
60
(2.36)
142
(5.59)
288
(11.34)
411
(16.18)
349
(13.74)
288
(11.34)
143
(5.63)
26
(1.02)
17
(0.67)
1,800
(70.87)
Avg.rainy days(≥ 1.0 mm) 1.2 2.2 3.0 4.8 8.7 14.7 20.5 20.2 15.7 8.1 1.5 0.9 101.5
Avg.relative humidity(%) 66 58 58 66 70 77 83 83 81 73 67 68 71
Mean monthlysunshine hours 203.9 201.2 225.8 235.4 227.1 123.1 93.1 104.9 116.2 182.6 190.8 203.4 2,107.5
Source #1: NOAA[77]
Source #2: India Meteorological Department
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