Water stress

Water stress

As the global population grows and the demand for water increases, there will be less water per person.
For water-rich countries such as Canada or Brazil this decrease is not a serious worry, but elsewhere it can be life-threatening.
Globally, half a billion people – most of them living in Africa and the middle east – are chronically short of water.
There are insufficient renewable supplies of water in China and parts of Europe, while India looks set to suffer considerable water stress in the future.
Even in the USA, where water is relatively abundant, availability will have halved between 1955 and 2055, most obviously in the dry southwest.
At present, more than one-third of the world’s population is short of water, and it is estimated this will reach 45% by 2025.
The United Nations Food and Agriculture Organisation (FAO) expects water demand to reach 5,235 km3 per year by 2025.
Agriculture
1. Agriculture is the major user of water, particularly as we struggle to increase food supplies for a growing global population
2. Currently, agriculture uses 69% of the world’s 4,430.7 km3 a year freshwater supply.
3. A kilogram of beef, for example, is ten times more ‘water-costly’ to produce than a kilogram of rice.
4. Some forms of agriculture are less water-efficient than others.
5. At present, 17% of the global area devoted to growing crops is irrigated
6. While water storage and irrigation systems do make agriculture more productive, they can also be wasteful of water.
7. While water storage and irrigation systems do make agriculture more productive, they can also be wasteful of water.
Industry
1. The proportion of water used globally by industry (21%) rose relatively slowly during the twentieth century, mainly in the developed countries of Europe, Russia, Canada and the USA.
2. Estimates for the coming decade suggest a more rapid global rise, driven by large-scale industrialisation in countries such as India and China.
3. Hydroelectric power (HEP) continues to use huge amounts of water, but this water is available to other users once it has passed through the turbines.
4. Industry is generally a much more efficient user of water than agriculture, but there aresome significant exceptions: paper manufacturing, for example, is one of the most extravagant users of water on the planet.
5. Industry has also caused significant water pollution problems.
Domestic
1. Water usage in homes is the smallest category of consumption, using only 10%.
2. The amount used, however, varies enormously from country to country.
3. Most developed countries need at least 100,000 litres of water per person per year, while in most African countries the figure is less than 50,000 litres.
4. Global domestic demand seems to be doubling every 20 years and it is arguably only the poor access in Africa that is limiting growth in demand there.
5. The quality of the water involved also varies considerably.
Water Sources
1. Surface Water
  1. Rivers, lakes and reservoirs provide large amounts of surface water for a wide variety of uses.
  2. So called ‘mega-dams’ are found on most of the world’s major rivers.
  3. Half of all the world’s dams (around 50,000) are in China, the USA, India and Japan, and their reservoirs account for a quarter of the global freshwater supply.
  4. The construction of reservoirs brings short-term economic gains in terms of water supply, hydroelectric power and flood control, but these must be measured against their longer-term environmental and social impacts.
  5. Large-scale river-water diver- sions and wetland drainage programmes also have costs and benefits.
2. Aquifers
  1. Underground supplies from aquifers are the sole source of drinking water for about a quarter of the world’s population.
  2. Three-quarters of Europe’s drinking water comes from groundwater, while Bangladesh and India use most of their ground- water for irrigation.
  3. In many countries, for example the USA, China and India, as well as in much of the middle east, water is being abstracted from aquifers faster than it is being replaced.
  4. The long-term costs of this over-abstraction are dwindling supplies, falling water tables and seawater contamination.
Pressure on water supplies
1. In many parts of the world there is a growing mismatch between water supply and demand. This can be seen locally and across whole regions
2. Water stress is the term used when the annual supply of water per person falls below 1,700 m3. When this figure drops below 1,000 m3, the term used is water scarcity. There are two types of water scarcity:
  1. Physical Scarcity
    1. occurs when more than 75% of a country or region’s river flows are being used.
    2. A quarter of the world’s population lives in such areas, which include parts of the USA and Australia.
  2. Economic Scarcity
    1. Occurs when the development of blue water flow sources is limited by human and financial capacities.
    2. More than 1 billion people, in areas such as sub-Saharan Africa, use less than 25% of the river resources available.
India
1. India has 4% of the world’s freshwater, but 16% of its population.
2. Demand will probably exceed supply by 2020, as urban water demand is expected to double and industrial demand to triple.
3. Hydrologists calculate that 43% of precipitation never reaches rivers or aquifers, and water tables are falling rapidly as 21 million wells abstract water.
China
1. China has 8% of the world’s freshwater but must meet the needs of 22% of the world’s population.
2. Two-thirds of Chinese cities do not have enough water all year round, and national water supplies are likely to reach stress levels by 2030.
3. China uses irrigation to produce 70% of its food, mostly in the north and northeast, where the Yellow River and major aquifers are running dry.
4. Huge engineering projects will soon transfer vital water to this area from the water- rich south.
The water problems of the Beijing-Tianjin region
1. Beijing, China’s capital, may soon run out of water.
2. Each year, the gap between water demand and supply widens, wells dry up, groundwater and rivers become polluted and ground subsidence worsens.
3. Why this is happening
  1. The causes of this deteriorating situation are both physical and human.
  2. Northeast China, where Beijing is located, is prone to floods and, in recent years, droughts.
  3. Most precipitation falls between July and September, sometimes more than half of it within 3 days.
  4. Several wet years can be followed by several dry years.
  5. The capital’s population of 16 million makes it the second largest city after Shanghai.
  6. On the coast, not far from Beijing, is China’s third largest city, Tianjin (population 11 million), a major port with heavy industry, commerce and developing services.
  7. Beijing’s annual population growth rate is stabilising at about 2.5% as a result of efforts by the govern- ment to restrict family size, but rural–urban migrants continue to arrive. The situation in Tianjin is similar.
4. Water Supply
  1. Beijing draws 60% of its water supply from aquifers.
    1. These are overexploited, but the water quality is still acceptable.
  2. In the late 1970s and early 1980s, a series of droughts led to increased demands for irri- gation water.
    1. This lowered the water table in some areas by as much as 40 m, and some wells were pumped down to the bedrock.
  3. Much of Beijing has subsided by between 0.5 m and 1 m per year because of all this abstraction.
  4. ianjin relies on groundwater for about 30% of its water supply, but salt water incursion makes the water brackish.
  5. Surface water supply in the region depends on five major rivers which enter the Hai He river system.
  6. Upstream withdrawals and contamination of these rivers have a negative effect on downstream cities, and Beijing also makes Tianjin’s water problems worse by the scale of its abstractions and pollution.
  7. An aqueduct 2,500 km long has been built, the first phase of a scheme to divert water from the Three Gorges Dam to the Beijing–Tianjin region.
  8. Projects to improve water quality and conserve water have also been implemented.
5. Demand for water
  1. Industrial output in the region has increased more than sixfold in the last 20 years.
  2. Water demand in the Beijing–Tianjin region is currently 4.9 billion m3 per year and continues to rise.
    1. Of this, agriculture accounts for about 65%, although the use of water-saving technologies means irrigation demands are levelling off.
  3. Water demand has not risen as fast as this as industries have become more water-efficient and recycle their waste water and there has been a shift from heavy to high-tech industry.
  4. The fastest rate of increase is in domestic water use: consumption has risen tenfold in the last 50 years and now aver- ages 240 litres per person per day.

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	Criado por Jodie Goodacre quase 11 anos atrás