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).
Much of the city was originally a wetland that was reclaimed over the decades to accommodate a burgeoning population.
The remaining undeveloped areas, known as the East Kolkata Wetlands
, were designated a “wetland of international importance” by theRamsar Convention
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.
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.
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
trap and 600–800 m (1,970–2,620 ft) permian
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.
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
according to a United Nations Development Programme
report, its wind and cyclone zone is “very high damage risk”.
The Kolkata metropolitan area
is spread over 1,886.67 km2
(728.45 sq mi):7
and comprises 3 municipal corporations (including Kolkata Municipal Corporation), 39 local municipalities
and 24 panchayat samitis
, as of 2011.:7
The urban agglomeration encompassed 72 cities and 527 towns and villages, as of 2006.
Suburban areas in the Kolkata metropolitan area incorporate parts of the following districts: North 24 Parganas
, South 24 Parganas
, Hooghly, and Nadia
Kolkata, which is under the jurisdiction of theKolkata Municipal Corporation
( KMC), has an area of 185 km2
(71 sq mi).
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).
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
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.
The West Bengal Secretariat
, General Post Office
, Reserve Bank of India
, High Court
, Lalbazar 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 Road
, Camac Street
, Wood Street, Loudon Street, Shakespeare Sarani
, and A. J. C. Bose Road
is a large open field in the heart of the city that has been called the “lungs of Kolkata”
and accommodates sporting events and public meetings.
and Kolkata Race Course
are 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 Ballygunge
, Jodhpur Park
, Lake Gardens, Golf Green
, and Kasba
From south-west to south-east, outlying areas include Garden Reach, Behala
, Thakurpukur, Kudghat,Ranikuthi
, 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.
In the 2000s, Sector V in Bidhannagar developed into a business hub for information technology and telecommunication companies.
Both Bidhannagar and New Town are situated outside the Kolkata Municipal Corporation limits, in their own municipalities.
Fort William, on the western part of the city, houses the headquarters of the Eastern Command
of the Indian Army
its premises are under the jurisdiction of the army.
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).
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.
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).
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
), or “Nor’westers” in English.
Rains brought by the Bay of Bengal branch of the south-west summer monsoon
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.
Kolkata has been hit by several cyclones; these include systems occurring in 1737 and 1864 that killed thousands.
is a major concern in Kolkata. As of 2008, sulphur dioxide
and nitrogen dioxide
annual concentration were within the national ambient air quality standards of India, but respirable suspended particulate matter
levels were high, and on an increasing trend for five consecutive years, causing smog and haze.
Severe air pollution in the city has caused a rise in pollution-related respiratory ailments, such as lung cancer.