Water supply and Demand Flashcards
Water comes from various sources
Water can be extracted from both surface and underground sources. The process of removing water from water sources is called abstraction.
Surface resources include rivers, lakes, melting glaciers and reservoirs.
Reservoirs are man-made lakes - they are usually made by building a dam across a river, which traps water so it can be used by people.
Climate-Physical factor
Most places rely on rainfall for their water supply. Areas with high rainfall generally have a more reliable water supply.
In hot climates, lots of water is lost from lakes and rivers due to evaporation, which can cause water scarcity.
Very high rainfall can overwhelm sewers and water treatment plants and can increase surface runoff from fields and urban areas - this can reduce water quality as more pollutants end up in water supplies.
Geology-Physical factor
When rain falls on impermeable rock (e.g. clay) it can’t soak in, so it flows into rivers and lakes.
When rain falls on permeable rock, e.g. sandstone, it flows through them and can form aquifers - water is harder to extract from these, but they can make water available in very dry places.
Some types of rock contain salts and minerals that dissolve into the water, sometimes making it unsuitable for drinking without lots of treatment.
Drainage-Physical factor
Drainage systems move water from one area to another, changing the distribution of water.
Large drainage basins cover more land, so are more likely to receive a lot of rainfall, increasing water supply.
In some areas, drainage systems don’t have enough capacity to cope with heavy rainfall-this can cause sewage systems to overflow, affecting water quality.
Human Factors
Increasing demand is reducing supplies, eg, extracting groundwater limits recharge of lakes and rivers.
Human activities such as farming and industry can pollute water supplies, e.g. runoff from farmland can result in high concentrations of fertilisers and pesticides in water, making it unsuitable for many uses.
As water supplies are reduced, the price of water may increase, making it inaccessible for some people.
Water used in many different industries
Farming - Farms use water to irrigate crops and raise livestock.
Electricity generation - Water is heated in many types of power station to generate steam to drive turbines which generate electricity. It’s also used to directly drive turbines in hydro-electric plants.
Manufacturing-Factories of all kinds use water in the production of their products, e.g. paper factories use it to produce the wood pulp that’s used to make sheets of paper. Many factories use it for cooling machinery.
Trade-Waterways and oceans enable the transport of goods within and between countries.
Water Availability
Some countries have lots of water available,
Canada, New Zealand — annual rainfall is quite high, and low or moderate temperatures limit evaporation.
Water availability is much lower in other areas, e.g.:
Egypt - has an arid climate and inadequate water treatment facilities.
Jordan has an arid climate. There is over-abstraction of water upstream, reducing water availability (see p.224).
Water demand
Some countries have high demand for water, e.g.:
USA, Argentina - lots of farming, mining and industry, which use lots of water.
Other countries use much less water, e.g.:
Angola, Papua New Guinea - poor water infrastructure (e.g. broken pipes) and high prices limit access to water, so people can’t use much.
Water stress
When demand for water exceeds supply, or when water is not of high enough quality to use, places experience water stress.
Physical supplies-water trade
This can be trade of physical supplies -for example, Singapore has very limited natural water reserves, but it ensures adequate water availability by importing around half of the water it needs from Malaysia.
Water transfer-water trade
Water transfer is another way of moving water from places where there is plenty to places where there is not enough. For example, Spain transfers large amounts of water from the Tagus river basin to Murcia, Alicante and Almeria, in the dry south-east.
rights to extract-water trade
Rights to extract water can also be bought and sold - for example, in the Murray-Darling Basin in southern Australia, individuals and organisations can buy and sell the right to use a share of the available water.
Changes upstream can have a major impact downstream
For example, over-abstraction can result in low flows downstream, industry can increase pollution, and farming can increase soil erosion and therefore suspended sediment concentration. This means that countries or regions upstream must manage rivers carefully to avoid knock-on effects for downstream areas.
Many rivers cross international boundaries.
e.g. the River Nile flows through nine countries. This can give upstream countries power over downstream countries, and failure to manage water resources properly can cause disputes or conflict between countries. For example, in 2015 a dispute between Iran and Afghanistan over water rights from the Hari Rud River led to the killing of Afghan villagers trying to extract water from the river.
