London is the capital city of England and the United Kingdom

by gently rolling hills including Parliament Hill, Addington Hills, and Primrose Hill. The Thames was once a much broader, shallower river with extensive marshlands; at high tide, its shores reached five times their present width.

 Since the Victorian era the Thames has been extensively embanked, and many of its London tributaries now flow underground. The Thames is a tidal river, and London is vulnerable to flooding. The threat has increased over time due to a slow but continuous rise inhigh water level by the slow 'tilting' of Britain (up in the north and down in the south) caused by post-glacial rebound.

In 1974, a decade of work began on the construction of the Thames Barrier across the Thames at Woolwich to deal with this threat. While the barrier is expected to function as designed until roughly 2070, concepts for its future enlargement or redesign are already being discussed.

Climate

London has a temperate oceanic climate, similar to much of southern Britain. Despite its reputation as being a rainy city, London receives less precipitation in a year than Rome at 834 mm (32.8 in), or Bordeaux at 923 mm (36.3 in). Winters are generally chilly to cold with frost usually occurring in the suburbs on average twice a week from November to March. Snow usually occurs about four or five times a year mostly from December to February. Snowfall during March and April is rare but does occur every two or three years. Winter temperatures seldom fall below −4 °C (24.8 °F) or rise above 14 °C (57.2 °F). During the winter of 2010, London experienced its lowest temperature on record (−14 °C(6.8 °F)) in Northolt and the heaviest snow seen for almost two decades, a huge strain on the city's transport infrastructure. Temperature extremes for all sites in the London area range from 38.1 °C (100.6 °F) at Kew during August 2003, (which has been proposed to be the UK's highest 'accurate' temperature) down to −16.1 °C (3.0 °F) at Northolt during January 1962. Temperature's of below −20 °C (−4.0 °F) have been noted prior to the 20th century, but the accuracy cannot be validated.

Summers are generally warm and sometimes hot, the heat being boosted by the urban heat island effect making the centre of London at times 5 °C (9 °F) warmer than the suburbs and outskirts. London's summer average is 24 °C (75.2 °F). On average there are 7 days a year above 30 °C (86.0 °F) and 2 days a year above 32 °C (89.6 °F). Temperatures of 26 °C (80 °F) usually occur on a weekly basis from mid- June to late August.

During the 2003 European heat wave there were 14 consecutive days above 30 °C (86.0 °F) and 2 consecutive days where temperatures soared up to 38 °C (100.4 °F), leading to hundreds of heat related deaths. Rain generally occurs on around 2 out of

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