Topography

Sydney is a coastal basin with the Tasman Sea to the east, the Blue Mountains to the west, the Hawkesbury River to the north, and the Woronora Plateau to the south.

Sydney spans two geographic regions. The Cumberland Plain lies to the south and west of the Harbour and is relatively flat. The Hornsby Plateau is located to the north and is dissected by steep valleys. The flat areas of the south were the first to be developed; it was not until the construction of the Sydney Harbour Bridge that the northern reaches became more heavily populated. Seventy surf beaches can be found along its coastline, with Bondi Beach being the most famous.

The Nepean River wraps around the western edge of the city and becomes the Hawkesbury River before reaching Broken Bay. Most of Sydney's water storages can be found on tributaries of the Nepean River. The Parramatta River is mostly industrial and drains a large area of Sydney's western suburbs into Port Jackson. The southern parts of the city are drained by the Georges River and the Cooks River into Botany Bay.

There is no single definition of the boundaries of Sydney. The Australian Statistical Geography Standard definition of Greater Sydney covers 12,369 km² (4,776 sq mi) and includes the local government areas of Central Coast in the north, Hawkesbury in the north-west, Blue Mountains in the west, Sutherland Shire in the south, and Wollondilly in the south-west.^[96] The local government area of the City of Sydney covers about 26 square kilometres from Garden island in the east to Bicentennial Park in the west, and south to the suburbs of Alexandria and Rosebery.^[97]

Geology

Sydney is made up of mostly Triassic rock with some recent igneous dykes and volcanic necks (typically found in the Prospect dolerite intrusion, west of Sydney).^[98] The Sydney Basin was formed in the early Triassic period.^[99] The sand that was to become the sandstone of today was laid down between 360 and 200 million years ago. The sandstone has shale lenses and fossil riverbeds.^[99]

The Sydney Basin bioregion includes coastal features of cliffs, beaches, and estuaries. Deep river valleys known as rias were carved during the Triassic period in the Hawkesbury sandstone of the coastal region. The rising sea level between 18,000 and 6,000 years ago flooded the rias to form estuaries and deep harbours.^[99] Port Jackson, better known as Sydney Harbour, is one such ria.^[100] Sydney features two major soil types: sandy soils (which originate from the Hawkesbury sandstone) and clay (which are from shales and volcanic rocks), though some soils may be a mixture of the two.^[101]

Directly overlying the older Hawkesbury sandstone is the Wianamatta shale, a geological feature found in western Sydney that was deposited in connection with a large river delta during the Middle Triassic. The Wianamatta shale generally comprises fine grained sedimentary rocks such as shales, mudstones, ironstones, siltstones and laminites, with less common sandstone units.^[102] The Wianamatta Group is made up of Bringelly Shale, Minchinbury Sandstone and Ashfield Shale.^[103]

Ecology

The most prevalent plant communities in the Sydney region are grassy woodlands (i.e. savannas)^[104] and some pockets of dry sclerophyll forests,^[105] which consist of eucalyptus trees, casuarinas, melaleucas, corymbias and angophoras, with shrubs (typically wattles, callistemons, grevilleas and banksias), and a semi-continuous grass in the understory.^[106] The plants in this community tend to have rough, spiky leaves due to low soil fertility. Sydney also features a few areas of wet sclerophyll forests in the wetter, elevated areas in the north and northeast. These forests are defined by straight, tall tree canopies with a moist understory of soft-leaved shrubs, tree ferns and herbs.^[107]

The predominant vegetation community in Sydney is the Cumberland Plain Woodland in Western Sydney (Cumberland Plain),^[108] followed by the Sydney Turpentine-Ironbark Forest in the Inner West and Northern Sydney,^[109] the Eastern Suburbs Banksia Scrub in the coastline and the Blue Gum High Forest scantily present in the North Shore – all of which are critically endangered.^[110]^[111] The city also includes the Sydney Sandstone Ridgetop Woodland found in Ku-ring-gai Chase National Park on the Hornsby Plateau to the north.^[112]

Sydney is home to dozens of bird species,^[113] which commonly include the Australian raven, Australian magpie, crested pigeon, noisy miner and the pied currawong. Introduced bird species ubiquitously found in Sydney are the common myna, common starling, house sparrow and the spotted dove.^[114] Reptile species are also numerous and predominantly include skinks.^[115]^[116] Sydney has a few mammal and spider species, such as the grey-headed flying fox and the Sydney funnel-web, respectively,^[117]^[118] and has a huge diversity of marine species inhabiting its harbour and beaches.^[119]

Climate

Under the Köppen–Geiger classification, Sydney has a humid subtropical climate (Cfa)^[120] with "warm, sometimes hot" summers and "generally mild",^[121]^[122]^[123] to "cool" winters.^[124] The El Niño–Southern Oscillation, the Indian Ocean Dipole and the Southern Annular Mode^[125]^[126] play an important role in determining Sydney's weather patterns: drought and bushfire on the one hand, and storms and flooding on the other, associated with the opposite phases of the oscillation in Australia. The weather is moderated by proximity to the ocean, and more extreme temperatures are recorded in the inland western suburbs.^[127]

At Sydney's primary weather station at Observatory Hill, extreme temperatures have ranged from 45.8 °C (114.4 °F) on 18 January 2013 to 2.1 °C (35.8 °F) on 22 June 1932.^[128]^[129]^[130] An average of 14.9 days a year have temperatures at or above 30 °C (86 °F) in the central business district (CBD).^[127] In contrast, the metropolitan area averages between 35 and 65 days, depending on the suburb.^[131] The hottest day in the metropolitan area occurred in Penrith on 4 January 2020, where a high of 48.9 °C (120.0 °F) was recorded.^[132] The average annual temperature of the sea ranges from 18.5 °C (65.3 °F) in September to 23.7 °C (74.7 °F) in February.^[133] Sydney has an average of 7.2 hours of sunshine per day^[134] and 109.5 clear days annually.^[4] Due to the inland location, frost is recorded early in the morning in Western Sydney a few times in winter. Autumn and spring are the transitional seasons, with spring showing a larger temperature variation than autumn.^[135]

Sydney experiences an urban heat island effect.^[136] This makes certain parts of the city more vulnerable to extreme heat, including coastal suburbs.^[136]^[137] In late spring and summer, temperatures over 35 °C (95 °F) are not uncommon,^[138] though hot, dry conditions are usually ended by a southerly buster,^[139] a powerful southerly that brings gale winds and a rapid fall in temperature.^[140] Since Sydney is downwind of the Great Dividing Range, it occasionally experiences dry, westerly foehn winds typically in winter and early spring (which are the reason for its warm maximum temperatures).^[141]^[142]^[143] Westerly winds are intense when the Roaring Forties (or the Southern Annular Mode) shift towards southeastern Australia,^[144] where they may damage homes and affect flights, in addition to making the temperature seem colder than it actually is.^[145]^[146]

Rainfall has a moderate to low variability and has historically been fairly uniform throughout the year, although in recent years it has been more summer-dominant and erratic.^[147]^[148]^[149]^[150] Precipitation is usually higher in summer through to autumn,^[122] and lower in late winter to early spring.^[125]^[151]^[127]^[152] In late autumn and winter, east coast lows may bring large amounts of rainfall, especially in the CBD.^[153] In the warm season black nor'easters are usually the cause of heavy rain events, though other forms of low-pressure areas, including remnants of ex-cyclones, may also bring heavy deluge and afternoon thunderstorms.^[154]^[155] Snowfall was last reported in 1836, though a fall of graupel, or soft hail, in the Upper North Shore was mistaken by many for snow, in July 2008.^[156] In 2009, dry conditions brought a severe dust storm towards the city.^[157]^[158]

More information Month, Jan ...

v t e Climate data for Sydney (Observatory Hill) 1991–2020 averages, 1861–present extremes
Month	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec	Year
Record high °C (°F)	45.8 (114.4)	42.1 (107.8)	39.8 (103.6)	35.4 (95.7)	30.0 (86.0)	26.9 (80.4)	26.5 (79.7)	31.3 (88.3)	34.6 (94.3)	38.2 (100.8)	41.8 (107.2)	42.2 (108.0)	45.8 (114.4)
Mean maximum °C (°F)	36.8 (98.2)	34.1 (93.4)	32.2 (90.0)	29.7 (85.5)	26.2 (79.2)	22.3 (72.1)	22.9 (73.2)	25.4 (77.7)	29.9 (85.8)	33.6 (92.5)	34.1 (93.4)	34.4 (93.9)	38.8 (101.8)
Mean daily maximum °C (°F)	27.0 (80.6)	26.8 (80.2)	25.7 (78.3)	23.6 (74.5)	20.9 (69.6)	18.3 (64.9)	17.9 (64.2)	19.3 (66.7)	21.6 (70.9)	23.2 (73.8)	24.2 (75.6)	25.7 (78.3)	22.8 (73.0)
Daily mean °C (°F)	23.5 (74.3)	23.4 (74.1)	22.1 (71.8)	19.5 (67.1)	16.6 (61.9)	14.2 (57.6)	13.4 (56.1)	14.5 (58.1)	17.0 (62.6)	18.9 (66.0)	20.4 (68.7)	22.1 (71.8)	18.8 (65.8)
Mean daily minimum °C (°F)	20.0 (68.0)	19.9 (67.8)	18.4 (65.1)	15.3 (59.5)	12.3 (54.1)	10.0 (50.0)	8.9 (48.0)	9.7 (49.5)	12.3 (54.1)	14.6 (58.3)	16.6 (61.9)	18.4 (65.1)	14.7 (58.5)
Mean minimum °C (°F)	16.1 (61.0)	16.1 (61.0)	14.2 (57.6)	11.0 (51.8)	8.3 (46.9)	6.5 (43.7)	5.7 (42.3)	6.1 (43.0)	8.0 (46.4)	9.8 (49.6)	12.0 (53.6)	13.9 (57.0)	5.3 (41.5)
Record low °C (°F)	10.6 (51.1)	9.6 (49.3)	9.3 (48.7)	7.0 (44.6)	4.4 (39.9)	2.1 (35.8)	2.2 (36.0)	2.7 (36.9)	4.9 (40.8)	5.7 (42.3)	7.7 (45.9)	9.1 (48.4)	2.1 (35.8)
Average rainfall mm (inches)	91.1 (3.59)	131.5 (5.18)	117.5 (4.63)	114.1 (4.49)	100.8 (3.97)	142.0 (5.59)	80.3 (3.16)	75.1 (2.96)	63.4 (2.50)	67.7 (2.67)	90.6 (3.57)	73.0 (2.87)	1,149.7 (45.26)
Average rainy days (≥ 1 mm)	8.2	9.0	10.1	7.9	7.9	9.3	7.2	5.6	5.8	7.6	8.7	7.9	95.2
Average afternoon relative humidity (%)	60	62	59	58	58	56	52	47	49	53	57	58	56
Average dew point °C (°F)	16.5 (61.7)	17.2 (63.0)	15.4 (59.7)	12.7 (54.9)	10.3 (50.5)	7.8 (46.0)	6.1 (43.0)	5.4 (41.7)	7.8 (46.0)	10.2 (50.4)	12.6 (54.7)	14.6 (58.3)	11.4 (52.5)
Mean monthly sunshine hours	232.5	205.9	210.8	213.0	204.6	171.0	207.7	248.0	243.0	244.9	222.0	235.6	2,639
Percent possible sunshine	53	54	55	63	63	57	66	72	67	61	55	55	60
Source 1: Bureau of Meteorology^[159]^[160]^[161]^[162]
Source 2: Bureau of Meteorology, Sydney Airport (sunshine hours)^[163]

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