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Like the rest of the Netherlands, South Holland experiences a temperate oceanic climate, a Cfb-class according to the Köppen climate classification. The climate is influenced by the North Sea and the Atlantic Ocean, which results in relatively cooler summers and milder winters. Rain showers are common in the fall and winter seasons. Because of the flat surface, wind storms are also not uncommon in the winter. Although rain occurs all year long, there is a relatively dryer period between April and September. Eastern winds can result in a temporary continental climate with relatively warm and dry summers and cold and stormy winters. The temperature varies between the 2 °C and 6 °C in the winter and 17 °C and 20 °C in the summer.
South Holland covers an area of 3,403 km2 (1,314 sq mi), of which 585 km2 (226 sq mi) is water. It borders the North Sea to the west, North Holland to the north, Utrecht and Gelderland to the east, and North Brabant and Zeeland to the south. Beside the dunes along the North Sea coast, the province is almost entirely flat and mostly consists of polders. The centre of South Holland and the area along the coast in the west are largely urban, part of the Randstad conurbation, while the east of the province is more agrarian and belongs to the Groene Hart, literally Green Heart. The south of the province is a collection of islands in the Rhine–Meuse–Scheldt delta. For census reasons, South Holland is divided into four regions: Rijnmond, South, West and East.
The Duin- en Bollenstreek is a region in the north-west of South Holland, around Katwijk, that features coastal dunes and the cultivation of flower bulbs. To the south of the region lie mostly pastures on sand soil, that form the transition to more urban area. This urban area runs along the Old Rhine, from Katwijk via Rijnsburg to Leiden and Zoeterwoude-Rijndijk. South of Leiden and north of The Hague lies an area where a landscape of dunes bordering the North Sea in the west transitions to one of peat more to the east. The easternmost tip of South Holland is part of De Biesbosch, one of the largest national parks of the Netherlands and one of the last freshwater tide areas in Europe. Other parks in South Holland, although no national parks, include Delftse Hout east of Delft, Ackerdijkse Plassen, a bird reserve north of Rotterdam,and Buytenpark and Westerpark near Zoetermeer.The Kagerplassen are a collection of lakes north-east of Leiden, popular for boating, watersports, fishing, camping and walking.
The southern part of South Holland consists of a number of islands of the Rhine–Meuse–Scheldt delta. Although technically islands in the sense that they are surrounded by rivers, canals or other bodies of water, most of these islands are well connected to the rest of the province via bridges, tunnels and dams. The southern islands, most notably Goeree-Overflakkee