Water: A renewable resource
Water is a key resource vital to life; it underpins society, economies and the environment. But it is a scarce resource.
Where has all the water gone?
Although rainfall, the main source of our supplies, is renewable through the water cycle, the amount of water circulating in this system is constant. The key issue is that demand for water is increasing and is exacerbating the imbalance between supply and demand.
Demand is driven by demography (population). During the 20th century, global population trebled while demand for water increased six-fold. Higher living standards, urbanisation and wasteful use of water pushed up average per-capita consumption. The greatest consumer of water globally is agriculture, which uses 70% of all water consumed – irrigation being the highest demand.
Demand is growing fastest in those areas of the world where water is already scarce. One third of the world’s population faced water stress in 2000 – ‘water stress’ is when water consumption exceeds 10% of the renewable supplies (or less than 1, 700 cubic metres of water per person). By 2050, the share of the world’s population facing water stress could increase fivefold.
Tackling the issues
Any development of water resources must take into account social and economic needs, and future growth. For the diverse economies of the developed world, it is essential that not too much water is removed as this affects both the land and the quality of water. Water quality is as important as quantity and over-abstraction affects both. Uncertainties such as changes in social and economic demand, and new national and global policies, make predicting both future demand and supply difficult. All are subject to climate change and new technologies. Rising needs for the scarce water resources require demand management. This aims to reduce the use of water by employing water-efficient technologies and economic measures.
The Middle East and North Africa (MENA)
This vast arid and semi-arid region, in terms of area, is the largest water-short region in the world. MENA has not been self-sufficient in water since the 1970s. High evaporation rates – between two and 20 times rainfall amounts – not only result in high water losses from reservoirs but also reduce rainfall effectiveness for crop growth. Only two major river systems, the Nile and Tigris-Euphrates, serve the region. Both rivers cross national boundaries meaning numerous demands are placed on the water source, while long-held local beliefs over water use make policy reform difficult.
Supply management and resource development
During the first half of the 20th century, rising water demands in the region were met by developing surface resources. In Egypt, for example, major dams were constructed on the Nile, Egypt’s only river, supplying 97% of the country’s water. Such dependence on the Nile for water led to the decision in the 1950s to build the High Aswan Dam. The dam – the last major one to be built on the Nile – impounds a reservoir (Lake Nasser) that stores three times Egypt’s annual share of the Nile’s flow. This ensures that water is not only available all year round but is also available in years of drought. The socio-economic benefits here have outweighed the environmental costs.
Hydro-electric power from the dam has made electricity available in rural areas. However, from 1950 to 2000, rising water demands in MENA were increasingly met by exploitation of groundwater resources. Diesel and electric pumps replaced traditional methods of lifting water and raised vast quantities of water. But over-pumping beneath the Nile delta and in other coastal areas has caused *saline water to pollute the water resources.
With natural resources over-stretched, governments are turning to non-conventional methods of providing new water. In Israel, the re-use of treated wastewater provides 15% of irrigation water. In some coastal areas in the MENA region, desalination of sea water provides urban areas with some drinking water and water for industry.
Demand management
In 1986, with no possibility of increasing natural resources, Israel opted for demand management to help address water scarcity. Savings in water use have been achieved by improving technical efficiency and using water-saving technologies in the home, industry and especially in agriculture. The other approach is allocative efficiency – transferring water from one sector of the economy to another sector – where water will gain higher economic returns. By reducing the amount allocated to agriculture, water has been made available for use in industry and service sectors that can employ greater numbers of people.
*Saline: containing salt
NB - this map is the most up-to-date (as of 2007) and is taken from the 2003 World Bank Atlas.
Case study: North plain of China
Water shortages are severe in the North China Plain. The two major cities, Beijing and Tianjin, have adopted water-efficiency measures but are already in crisis.
The Plain is one of the most densely populated areas of the country. An enormous population (300–325 million people – 25% of China’s total population), high levels of urbanisation and rapid rates of economic development mean water demands are high and rising, with agriculture making the greatest demand.
However, many are saying that the water transfer is not enough and that it’s too late to solve the water shortage. In the area where Beijing and Tianjin are located there are some cities which in five to seven years will run out of water. Please see the following article for further information:
http://news.bbc.co.uk/1/hi/world/asia-pacific/4754519.stm
Whare has all the water gone?
The Plain is the largest area of flat land in China but rainfall is unreliable and inadequate. Irrigation is widely used and demand for water for industrial and municipal uses is also increasing. The three major rivers – the Yellow, Hai and Huai – and aquifers (saturated permeable rocks) can no longer sustain the rate of abstraction.
Tackling the issues
To secure water and ensure socio-economic sustainability in the region, China has embarked on a major engineering scheme: the South North Water Transfer Project (SNWTP). Water is to be taken from the Yangtze, via three routes, to the Yellow river. Work has already started on the Eastern route, where water will be taken from the Yangtze, some 100km downstream from Nanjing, via the Grand Canal and other canals, rivers, lakes and reservoirs to Tianjin. In total, 50 billion m3 of water will be transferred annually from the Yangtze to the Yellow river.
This project is highly controversial. The issue of ecological dangers in transferring water from one river basin to another has been raised by environmental groups. But the scheme does address a number of important environmental issues. Without extra supplies of water, the Yellow river will increasingly suffer from reduced flows. These have already had serious effects on the environment as wetlands have been reduced and water pollution in the Yellow river have increased.
Case study: South-East England
This region, extremely small by comparison with the North Plain in China, also faces water shortage. The average rainfall total for London is 593mm, almost the same as the 539mm for Tel Aviv (Israel, in the MENA region).
Where has all the water gone?
Groundwater accounts for 90% of south-east England’s resources. A high population density and limited water resources mean that renewable water per person is extremely low at 921.8m3, which is about the same as the MENA region. By 2030, the number of people living in Kent is expected to rise by 29%. Furthermore, to comply with the UK’s National Environmental Programme, supplies from the North Kent Marshes and one catchment area of the North Downs will have to be reduced by 4 million litres a day to achieve environmental sustainability.
Tackling the issues
Demand management encourages the wise use of water. Public measures for water-use efficiency include metering (water-use billed by the drop) and garden sprinkler licences, while mandatory leakage control has reduced water loss by water companies. Resource development will be needed to avoid a water deficit – between 26 and 50 million litres of water a day – by 2030. Plans include raising the height of the dam on the Bewl Reservoir to increase storage capacity and building a new reservoir near Canterbury.
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