The Netherlands is geographically a very low and flat country, with about 26% of its area and 21% of its population located below sea level, and only about 50% of its land exceeding one metre above sea level. The country is for the most part flat, with the exception of foothills in the far southeast, up to a height of no more than 321 metres, and some low hill ranges in the central parts. Most of the areas below sea level are man-made, caused by peat extraction or achieved through land reclamation. Since the late 16th century, large polder areas are preserved through elaborate drainage systems that include dikes, canals and pumping stations. Nearly 17% of the country's land area is reclaimed from the sea and from lakes.
Much of the country was originally formed by the estuaries of three large European rivers: the Rhine (Rijn), the Meuse (Maas) and the Scheldt (Schelde), as well as their tributaries. The south-western part of the Netherlands is to this day a river delta of these three rivers, the Rhine-Meuse-Scheldt delta.
The Netherlands is divided into north and south parts by the Rhine, the Waal, its main tributary branch, and the Meuse. In the past these rivers functioned as a natural barrier between fiefdoms and hence historically created a cultural divide, as is evident in some phonetic traits that are recognisable on either side of what the Dutch call their "Great Rivers" (de Grote Rivieren). Another significant branch of the Rhine, the IJssel river, discharges into Lake IJssel, the former Zuiderzee ('southern sea'). Just like the previous, this river forms a linguistic divide: people to the northeast of this river speak Dutch Low Saxon dialects (except for the province of Friesland, which has its own language).
Over the centuries, the Dutch coastline has changed considerably as a result of natural disasters and human intervention. Most notable in terms of land loss was the storm of 1134, which created the archipelago of Zeeland in the south-west.
On 14 December 1287, St. Lucia's flood affected the Netherlands and Germany killing more than 50,000 people in one of the most destructive floods in recorded history. The St. Elizabeth flood of 1421 and the mismanagement in its aftermath destroyed a newly reclaimed polder, replacing it with the 72-square-kilometre (28 sq mi) Biesbosch tidal floodplains in the south-centre. The huge North Sea flood of early February 1953 caused the collapse of several dikes in the south-west of the Netherlands; more than 1,800 people drowned in the flood. The Dutch government subsequently instituted a large-scale programme, the "Delta Works", to protect the country against future flooding, which was completed over a period of more than thirty years.
The impact of disasters was to an extent increased through human activity. Relatively high-lying swampland was drained to be used as farmland. The drainage caused the fertile peat to contract and ground levels to drop, upon which groundwater levels were lowered to compensate for the drop in ground level, causing the underlying peat to contract further. Additionally, until the 19th century peat was mined, dried, and used for fuel, further exacerbating the problem. Centuries of extensive and poorly controlled peat extraction lowered an already low land surface by several metres. Even in flooded areas, peat extraction continued through turf dredging.
Because of the flooding, farming was difficult, which encouraged foreign trade, the result of which was that the Dutch were involved in world affairs since the early 14th/15th century.
To guard against floods, a series of defences against the water were contrived. In the first millennium AD, villages and farmhouses were built on man-made hills called terps. Later, these terps were connected by dikes. In the 12th century, local government agencies called "waterschappen" ("water boards") or "hoogheemraadschappen" ("high home councils") started to appear, whose job it was to maintain the water level and to protect a region from floods; these agencies continue to exist. As the ground level dropped, the dikes by necessity grew and merged into an integrated system. By the 13th century windmills had come into use to pump water out of areas below sea level. The windmills were later used to drain lakes, creating the famous polders.
In 1932 the Afsluitdijk ("Closure Dike") was completed, blocking the former Zuiderzee (Southern Sea) from the North Sea and thus creating the IJsselmeer (IJssel Lake). It became part of the larger Zuiderzee Works in which four polders totalling 2,500 square kilometres (965 sq mi) were reclaimed from the sea.
The Netherlands is one of the countries that may suffer most from climate change. Not only is the rising sea a problem, but erratic weather patterns may cause the rivers to overflow.
After the 1953 disaster, the Delta Works were constructed, a comprehensive set of civil works throughout the Dutch coast. The project started in 1958 and was largely completed in 1997 with the completion of the Maeslantkering. New projects have been periodically started since to renovate and renew the Delta Works. A main goal of the Delta project was to reduce the risk of flooding in South Holland and Zeeland to once per 10,000 years (compared to 1 per 4000 years for the rest of the country). This was achieved by raising 3,000 kilometres (1,864 mi) of outer sea-dykes and 10,000 kilometres (6,214 mi) of inner, canal, and river dikes, and by closing off the sea estuaries of the Zeeland province. New risk assessments occasionally show problems requiring additional Delta project dyke reinforcements. The Delta project is considered by the American Society of Civil Engineers as one of the seven wonders of the modern world.
It is anticipated that global warming in the 21st century will result in a rise in sea level. The Netherlands is actively preparing for a sea level rise (see Flood control in the Netherlands). A politically neutral Delta Commission has formulated an action plan to cope with a sea level rise of 1.10 metres (3.6 ft) and a simultaneous land height decline of 10 centimetres (3.9 in). The plan encompasses the reinforcement of the existing coastal defenses like dikes and dunes with 1.30 metres (4.3 ft) of additional flood protection. Climate change will not only threaten the Netherlands from the sea side, but could also alter rain fall patterns and river run-off. To protect the country from river flooding, another program is already being executed. The Room for the River plan grants more flow space to rivers, protects the major populated areas and allows for periodic flooding of indefensible lands. The few residents who lived in these so-called "overflow areas" have been moved to higher ground, with some of that ground having been raised above anticipated flood levels.
The predominant wind direction in the Netherlands is southwest, which causes a moderate maritime climate, with warm summers and cool winters, and typically high humidity. This is especially true close to the Dutch coastline, where the difference in temperature between summer and winter, as well as between day and night is noticeably smaller than it is in the southeast of the country.
Ice days (maximum temperature below 0 °C (32 °F)) usually occur from December until February, with the occasional rare ice day prior to or after that period. Freezing days (minimum temperature below 0 °C (32 °F)) occur much more often, usually ranging from mid-November to late March, but not rarely measured as early as mid-October and as late as mid-May. If one chooses the height of measurement to be 10 cm (4 in) above ground instead of 150 cm (59 in), one may even find such temperatures in the middle of the summer. On average, snow can occur from November to April, but sometimes occurs in May or October too.
Warm days (maximum temperature above 20 °C (68 °F)) in De Bilt are usually found in April to October, but in some parts of the country these warm days can also occur in March, or even sometimes in November or February (usually not in De Bilt, however). Summer days (maximum temperature above 25 °C (77 °F)) are usually measured in De Bilt from May until September, tropical days (maximum temperature above 30 °C (86 °F)) are rare and usually occur only in June to August.
Precipitation throughout the year is distributed relatively equally each month. Summer and autumn months tend to gather a little more precipitation than the other months, mainly because of the intensity of the rainfall rather than the frequency of rain days (this is especially the case in summer, when lightning is also much more frequent).
The number of sunshine hours is affected by the fact that because of the geographical latitude, the length of the days varies between barely eight hours in December and nearly 17 hours in June.
The Netherlands has 20 national parks and hundreds of other nature reserves, that include lakes, heathland, woods, dunes and other habitats. Most of these are owned by Staatsbosbeheer, the national department for forestry and nature conservation and Natuurmonumenten (literally 'Natures monuments'), a private organisation that buys, protects and manages nature reserves. The Dutch part of the Wadden Sea in the north, with its tidal flats and wetlands, is rich in biological diversity, and was declared a UNESCO World Heritage Nature Site in 2009.
The Oosterschelde, formerly the northeast estuary of the river Scheldt was designated a national park in 2002, thereby making it the largest national park in the Netherlands at an area of 370 square kilometres (140 sq mi). It consists primarily of the salt waters of the Oosterschelde, but also includes mud flats, meadows, and shoals. Because of the large variety of sea life, including unique regional species, the park is popular with Scuba divers. Other activities include sailing, fishing, cycling, and bird watching.
Phytogeographically, the Netherlands is shared between the Atlantic European and Central European provinces of the Circumboreal Region within the Boreal Kingdom. According to the World Wide Fund for Nature, the territory of the Netherlands belongs to the ecoregion of Atlantic mixed forests. In 1871, the last old original natural woods were cut down, and most woods today are planted monocultures of trees like Scots pine and trees that are not native to the Netherlands. These woods were planted on anthropogenic heaths and sand-drifts (overgrazed heaths) (Veluwe).
The Caribbean Netherlands are three islands designated as special municipalities of the Netherlands. The islands are part of the Lesser Antilles. The islands have maritime borders with France (Saint Barthélemy and Saint Martin), the United Kingdom (Anguilla), Venezuela, Saint Kitts and Nevis and the United States (US Virgin Islands).
Within this island group,
- Bonaire is part of the ABC islands within the Leeward Antilles island chain off the Venezuelan coast. The Leeward Antilles have a mixed volcanic and coral origin.
- Saba and Sint Eustatius are part of the SSS islands. They are located east of Puerto Rico and the Virgin Islands. Although in the English language they are considered part of the Leeward Islands, French, Spanish, Dutch and the English spoken locally consider them part of the Windward Islands. The Windward Islands are all of volcanic origin and hilly, leaving little ground suitable for agriculture. The highest point is Mount Scenery, 887 metres (2,910 ft), on Saba. This is the highest point in the country, and is also the highest point of the entire Kingdom of the Netherlands.
The islands of the Caribbean Netherlands enjoy a tropical climate with warm weather all year round. The Leeward Antilles are warmer and drier than the Windward islands. In summer, the Windward Islands can be subject to hurricanes.