The Netherlands and South Africa have ecosystems that are heavily dependent on human modification of the hydrosphere. The two regions face opposite water issues: the Netherlands has more water than it wants and Cape Town, South Africa, not enough. At this time, the ecological modifications in the Netherlands appear sustainable, whereas those in Cape Town appear unsustainable.

Sustainable Ecosystem: The Netherlands

The Dutch have modified their environment with two distinctive types of construction projects—polders and dikes. A polder is a piece of land that is created by draining water from an area. The Netherlands has 6,500 square kilometers (2,600 square miles) of polders, comprising 16 percent of the country’s land area.

Sustainable Water Management: The Netherlands

(a) The Dutch have considerably altered the site of the Netherlands through creation of polders and dikes. (b) Kalverpolder in North Holland has been created by pumping the water from the site into the canal, originally by means of windmills.

Polders, first created in the thirteenth century, were constructed primarily by private developers in the sixteenth and seventeenth centuries and by the government during the past 200 years. The Dutch government has reserved most of the polders for agriculture to reduce the country’s dependence on imported food. Some of the polders are used for housing, and one contains Schiphol, one of Europe’s busiest airports.

The second distinctive modification of the landscape in the Netherlands is the construction of massive dikes to prevent the North Sea, an arm of the Atlantic Ocean, from flooding much of the country. The Dutch have built dikes in two major locations—the Zuider Zee project in the north and the Delta Plan project in the southwest.

The Zuider Zee, a shallow bay of the North Sea, once threatened the heart of the Netherlands with flooding. A dike completed in 1932 caused the Zuider Zee to be converted from a saltwater sea to a freshwater lake called Lake IJssel. Some of the lake has been drained to create several polders.

A second ambitious project in the Netherlands is the Delta Plan. Several rivers that flow through the Netherlands to the North Sea split into many branches and form a low-lying delta that is vulnerable to flooding. After a devastating flood in January 1953 killed 1,836 people, the Delta Plan called for the construction of several dams to close off most of the waterways.

Once these two massive projects were finished, attitudes toward modifying the environment changed. To preserve the IJsselmeer’s recreation value, the Dutch scrapped plans to build more polders. The Dutch are deliberately breaking some of the dikes to flood fields. A plan adopted in 1990 called for returning 263,000 hectares (650,000 acres) of farms to wetlands or forests.

Global warming could threaten the Netherlands by raising the level of the sea around the country by between 20 and 58 centimeters (8 and 23 inches) within the next 100 years. Rather than build new dikes and polders, the Dutch have become world leaders in reducing the causes of global warming by acting to reduce industrial pollution and increase solar and wind power use, among other actions.

Unsustainable Ecosystem: Cape Town, South Africa

Cape Town, South Africa, an urban area of 3.8 million, has long been regarded as an example of sustainable development. But in 2018, the city nearly ran out of water, and may yet do so.

The city is located at the southwest tip of Africa on the edge of a very dry climate (refer to Figure 1-70). In recognition of the scarcity of water, Cape Town has practiced careful management of water supplies and other strong conservation policies. The city fixed leaks, replaced old pipes, installed meters, and adjusted prices to encourage conservation. Although the city’s population doubled between 1990 and 2018, its total consumption of water remained around the same. The city’s policies won it international awards for conservation and resource management.

Cape Town’s drinking water comes from several reservoirs that fill up with rainwater during the winter rainy season. In 2014, after a rainy winter, Theewaterskloof, the largest of these reservoirs, and the city’s principal source of drinking water, was full. Cape Town then suffered through its worst drought in more than 100 years. After two unusually dry years, the reservoir was still mostly full (Figure 1-76b). However, as the drought continued into early 2018, Theewaterskloof was only 13 percent of its level in 2014

Theewaterskloof Dam, Cape Town

Faced with a severe shortage of water, Cape Town ordered drastic cuts in water consumption. The result was to cut water consumption by one-half. Still, water supplies ran out periodically, requiring some people to line up for water

Cape Town faces an unsustainable future. Global climate change is making the region around the city drier and warmer. Thanks to higher rainfall, the reservoir level rose in 2018, though still lower than before the drought. But it can’t always count on winter rain to refill the reservoirs. The city needs to use groundwater and desalination of the sea water, but these projects are very expensive and would take many years to complete. Consequently, Cape Town—once internationally recognized for its sustainable policies—faces the prospect of recurring water supply crises year after year.

Telling Time

Earth as a sphere is divided into 360° of longitude (the degrees from 0° to 180° west longitude plus the degrees from 0° to 180° east longitude). As Earth rotates daily, these 360 imaginary lines of longitude pass beneath the cascading sunshine. If we let every fifteenth degree of longitude represent one time zone, and divide the 360° by 15°, we get 24 time zones, or one for each hour of the day. By international agreement, Coordinated Universal Time (UTC), known informally as Greenwich Mean Time (GMT), which is the time at the prime meridian (0° longitude), is the master reference time for all points on Earth.

Each 15° band of longitude is assigned to a standard time zone (Figure 1-78). The eastern United States, which is near 75° west longitude, is therefore 5 hours earlier than UTC (the 75° difference between the prime meridian and 75° west longitude, divided by 15° per hour, equals 5 hours). Thus when the time in New York City in the winter is 1:32 P.M. (or 13:32 hours, using a 24-hour clock), it is 6:32 P.M. (or 18:32 hours) UTC. During the summer, many places in the world, including most of North America, move the clocks ahead one hour; so in the summer when it is 6:32 P.M. UTC, the time in New York City is 2:32 P.M.

Time Zones

The International Date Line is an arc that for the most part follows 180° longitude. When the International Date Line is crossed heading east (toward America), the clock moves back 24 hours, or one entire day. When it is crossed heading west (toward Asia), the calendar moves ahead one day.

To see the need for the International Date Line, try counting the hours around the world from the time zone in which you live. As you go from west to east, you add 1 hour for each time zone. When you return to your starting point, you will reach the absurd conclusion that it is 24 hours later in your locality than it really is. Therefore—if it is 6:32 A.M. Monday in Auckland, when you get to Honolulu, it will be 8:32 A.M. Sunday because the International Date Line lies between Auckland and Honolulu.

The International Date Line for the most part follows 180° longitude. However, several islands in the Pacific Ocean belonging to the countries of Kiribati and Samoa as well as to New Zealand’s Tokelau territory, moved the International Date Line several thousand kilometers to the east. Samoa and Tokelau moved it in 2011 so that they could be on the same day as Australia and New Zealand, their major trading partners. Kiribati moved it in 1997 so that it would be the first country to see each day’s sunrise. Kiribati hoped that this feature would attract tourists to celebrate the start of the new millennium on January 1, 2000 (or January 1, 2001, when sticklers pointed out the new millennium really began). But it did not.

What is Time