Physical factors afffecting water supply.
There are 3 main physical factors affecting water supply: Climate, river systems and geology.
Climate: The distribution of water globally can be related to the Earth's climatic zones. Eg. Regions near to the equator often recieve high levels of annual percipitation whereas some areas of the tropics suffer from reccuring drought.
River Systems: The world's major rivers store and transfer water across continents. Eg. The amazon discharges an average of 219,000 m3 s-1. (This is 20% of all river water entering the ocean!)
Geology: When rocks underlying a river basin are inpermeable water will remain as surface run-off creating a high drainage density. Permeable soils and rocks allow water to pass into underground storage called Aquifers.
How is water a finite resource? What problems can
Is Freshwater a finite resource? The amount of freshwater avaliable is finite. This is because the world's oceans hold 97.5% of all water so this water is saline and unfit for consumption. This means that only 2.5% of this water is potentially avaliable to us. However, 80% of the freshwater is trapped in icesnow and permafrost and just less than 20% is groundwater so only 1% of the world's water is easily accessible freshwater held in lakes, ecosystems, atmosphere and rivers.
Water stress: With the Global pop. growing and demand for water increasing there will be less water per person. Water rich countries such as Canada and Brazil don't have a problem but around half a billion people globally are short of water (mainly in Africa and the Middle East) and this is set to increase from a third to 45% by 2025.
Why is water demand increasing?
There are 3 main areas where water demand is increasing: Agriculture, Industry and Domestic uses.
Agriculture: Agriculture is a major user of water. They currently use 69% of the world's freshwater supply particularly as we are trying to increase food supplies for a growing pop. Some forms of agriculture are more ' water costly' than others. Eg. Beef is ten times as w.costly than rice. The water used to produce products is called virtual water. Irrigation, although it makes agriculture more productive, can be wasteful of water. This is through poor management leading to: evaporation, seepage, salinisation and fertiliser pollution.
Industry: The proportion of water used globally by industry is 21%. HEP continues to use huge amounts of water but this is avaliable to other users after it has passed through the turbines. As a rule Industry tends to be a more efficent user of water than agriculture, however, paper manufacturing uses very high amounts of water and other industry can pollute water resources.
Why is water demand increasing?
Domestic: Water usuage in homes (domestic) is the smallest catergory of consumption using only 10%. The amount used can vary enormously from country to country. Developed countries use around 100,000L per person per year whereas Developing countries use less than 50,000L. Global domestic demand is doubling every 20 years. The quality of water involoved varies considerably.
Our water supply comes from 2 sources: Surface Water and Underground Aquifers.
Surface Water: Rivers, lakes and resevoirs provide large amounts of surface water for a variety of uses. Mega-dams are found on most of the worlds major rivers. 1/2 of the world's dams are found in China, USA, India and Japan accounting for a 1/4 of the global fresh water supply.
Aquifers: These are underground supplies which is the sole source of drinking water for around 1/4 of the world's pop. 3/4 of Europe's drinking water comes from groundwater while Bangladesh and India mainly uses groundwater for crop irrigation. In many places such as the USA water is being taken faster than it is being replaced (over-abstraction) leading to dwindling supplies, falling water tables and seawater contamination.
Pressure on Water supplies.
There is a growing mis-match of water supply and demand. The term water stress is used when annual supply of water per person falls below 1700m3. When this figure drops below 1000m3 we call this water scarity. This can be defined in 2 ways:
Physical Scarity: occurs when more than 75%of a country's river flows are being used. 1/4 of the global pop. live in such areas (USA and Australia)
Economic Scarity: occurs when the development of blue water flow sources is limited by human and finacial capacities. More than 1 billion people live in areas such as Sub-Saharan Africa use less than 25% of river resources avaliable.
Examples India and China.
Rapid economic growth is putting enormous pressure on water supplies.
India: India has 4% of the world's freshwater but 16% of the population. Demand will probably exceed supply by 2020 as urban demand is expected to double and industry demand is expected to triple. Hydrologists calculate that 43% of percipitation never reaches aquifers or rivers and water wells are falling rapidly as 21 million wells abstract water.
China: China has 8% of the world's freshwater and 22% of the world's pop. 2/3 of Chinese cities don't have enough water all year round and national supply is likely to reach stress levels by 2030. China uses irrigation to produce 70% of its food so the Yellow River and major Aquifers are running dry.
Human Impact on water avalibility.
Human Impacts can have a negative effect on water avaliability.
Pollution: Industry often pumps its waste chemicals untreated into the rivers and oceans. This causes the water to effect eco-systems and makes the water unusable for human consumption or even irrigation.
Abstraction: Removing water from rivers and groundwater supplies for drinking water or irrigation can have negative impacts. Water is being extracted from aquifers faster than it can be replaced. Arid areas may never replace the water. Also, the removal of fresh water in coastal areas can unbalance the natural ratio leading salt water incursion and salinisation of wells.
The Water Poverty Index and Poverty.
The Index uses 5 parameters: Resources, Access, Capacity, Use and the Enviroment. Each parameter is scored out of 20 giving an overall score of 100.
Poverty: Lack of water hampers attempts to reduce poverty and encourage development. Improved water supply and sanitation can improve food supply, bring better health and higher standards of wellbeing. Water wealth in developed countries brings cheap water, irrigation, energy and economic growth.