The Hydrological Cycle
The Hydrological Cycle on a global scale is a closed system, this means that no water is ever added or lost from the cycle - it just goes round and round. The Earth never gets wetter or drier.
Water can be stored in lakes, rivers and oceans as well as in rocks and the soil. The soil, lakes and rocks store relatively small amounts of fresh water but are in high demand as water sources.
Transfers/Flows of water include - Surface run off, through flow, groundwater flow, infiltration and precipitation.
Green water is water that never reaches the ground, it is intercepted by trees and then evaporates off of the leaves.
Blue water reaches the grounds surface and is usually stored in lakes and rivers.
Why an area would have an unreliable water supply
Water stress occurs when the demand for water is greater than the supply or when the quality of water is not good enough to use.
Increased demand for water causes water stress, this is due to:
Increased demand as population increases,
Increased demand from agriculture - irrigating crops uses huge amounts of water,
Supplies are becoming increasingly unpredictable,
Possibility of water wars in the Middle East - fighting over water,
Economic development in China and India leads to an increased demand for water,
Rising living standards means people use more water for washing etc.
There is a decline in water availability due to:
Energy - reservoir storage for HEP, water lost through evaporation,
Climate change means that rain supplies are less reliable in some areas,
Tourism - hotels, golf courses etc. use huge amounts of water.
Only half of the blue water (fresh water run off) is used as most of it is inaccessible.
The Sahel is a belt of semi-arid land south of the Sahara, Africa. The land covers 14.9 billion hectares of the Earth's surface.
The countries comprising sub-Saharan Africa depend more on their natural resource base for economic and social needs more than any other region in the world. Two thirds of sub-Saharan Africa's people live in rural areas and reply on agriculture and other natural resources for income. Environmental problems of sub-Saharan Africa include air and water pollution, deforestation, loss of soil and soil fertility and a dramatic decline in biodiversity throughout the region.
Causes of water stress include:
It only rains one or two months in a year, total of 250-450 mm/year,
Since 1970 rainfall has been below average, some years 25% less than average,
Sometimes rainfall is so heavy that most is lost as surface run off leading to floods,
Some years there is no rain at all - this leads to rivers drying up, water tables fall, farmers crops fail, animals die, desertification, decreased food supplies and finally famine.
Rapidly growing population which puts increased pressure in drought years on failing food supplies,
Global warming may reduce the amount of water available.
Physical water scarcity - The demand is greater than the availability,
Economic water scarcity - People can't afford to exploit the water supply available.
Impact of climate change on water supplies
Social - Huge populations such as Arizona rose 40% in 1990s so they must be reliant on smaller water sources.
Economic - Authorities having to pay for solutions such as drought tolerating landscaping, long-term decline in tourism in areas such as Las Vegas.
Environmental - Reduced rainfall to areas that are usually scarce such as the South-West, Drought conditions were experienced in 2002, 2004 and 2007.
Social - half of the world's population is at risk, billions of people could have reduces water supplies and there is a risk of starvation as subsistence farmers are no longer able to supply water to crops.
Economic - Increased dependency on aid from other countries and the World Bank.
Environmental - Major rivers fed by seasonal melting of glaciers ensure a sustainable water supply - climate change could lead to permanent melting, increase in extreme weather events and increased sea level could lead to flooding in low lying area.
It is predicted that in the future in the UK, Summers will be longer and hotter - especially in London and the South East, this enables the growth of different crops such as grapes. Warmer, wetter winters with more rain bearing storms all over the UK could fill reservoirs with more water for supplies.
How humans reduce the quality of water through pol
Sources of pollution include: Salt run off from roads, sewage, run off from building sites, industrial discharge, chemicals applied to golf courses, crop spraying, fertilisers washed in, cattle waste (slurry) and disposal of hazardous waste in rivers.
The biggest sources of water pollution are found in rapidly developing countries such as China and India - they put economic growth before environmental problems. The rapidly growing cities mean slums around the outskirts and badly pollute streams as there are no sewage systems in place. Chemicals added to the crops run off in water sources.
Developed countries such as the UK and Japan have taken big steps to control pollution. Tertiary and quaternary industries cause less pollution than primary and secondary.
Water pollution in the River Rhine
The Rhine is one of the longest rivers in Europe and runs for over 1,300 kilometres from its source in Switzerland.
Causes of the pollution include:
Many types of industries establishing themselves along the banks of the rivers. The chemical industry disposes of waste containing heavy metals such like cadmium, lead and mercury. The paper-making, brewing and detergents industries dump their waste into the river. Although most of these emissions are properly authorised, some aren't and there is always the risk of an accidental leak or spill. Households dispose of a variety of waste products, they often throw things directly into the rivers. Many agricultural practices lead to organic waste, chemical fertilisers and other waste products reaching the river. Fertilisers contain various chemicals from phosphates and nitrates to poisonous hydrocarbons
The impacts of water pollution include:
Metals such as lead and cadmium which pollute the river attach themselves to silt particles and hence the polluted silt cannot be dumped in the North sea. Public health would be seriously affected if the water isn't purified. Phosphates stimulate the growth of algae which eventually clogs pipelines and filters - silt poses a similar problem. The high salinity of the water not only gives the water a displeasant taste, but also helps to corrode the pipelines. Saline discharges from mines in Germany make the water unsuitable for market gardening in the Netherlands. Hence, Dutch market gardeners have to desalinate water before using it to water their crops - this is expensive.
How Humans use of stores and flows can reduce wate
How people intervene in the water cycle:
Cloud seeding - making it rain
Deforestation - decreased interception leads to an increase of flooding,
Urbanisation - increased impermeable surfaces,
Over abstraction - taking too much water from rivers and lakes,
Building dams and reservoirs,
Global warming - glaciers melt
NAMED EXAMPLE - Thames Valley, South England
Dramatic decrease in river flow, tributaries dried up and ecosystem damaged. Droughts and increased demand from more homes leads to an increased use of groundwater supplies leading to a falling water table so the store of water is not used sustainably.
Most water companies now have strict policies for managing water levels (CAMS - Catchment Abstraction Management Strategies).
This adds a new store to the hydrological cycle but bring problems such as:
Loss of land - drowns villages and farmland,
Disease - stagnant water leads to mosquitoes,
Drowned vegetation releases methane which is a green house gas.
However, this also has its benefits such as:
Recreation - fishing, sailing, walking, wildlife.
Deforestation has it's disadvantages such as:
Fewer trees - less evapotranspiration, less green water recycles means less rain,
Soil left exposed to the sun and rain,
Less nutrients in the soil,
Raindrops wash out the finer soil, leaving a course, heavy surface,
Less interception means a greater flood risk.
Large scale water management schemes such as Dams have their advantages - increased water supply, recreational use, HEP industry, habitat for water birds and fishing. They also have disadvantages - loss of farmland and villages, less navigation, relocation of people occurs, disease due to stagnant water, loss of cultural sites and it interferes with fish migration.
Aswan Dam, Africa
The Aswan Dam is located on the River Nile which runs through Egypt. The dam is located here because the valley is narrow and deep from where it enters Egypt to Aswan, there were no major settlements around Aswan, the land around Aswan was of little agricultural value and the Aswan granite could be used in the construction of the dam.
It was completed in 1970 and provides Hydroelectric power, irrigation water for the surrounding farmland, water supply to the population, flood control - it is a multi purpose scheme.
There are both positive impacts such as:
Fish stocks in Lake Nasser, water is made available to homes and industries, electricity for home and farm use, irrigation water for nearby farms, new farmland created, flooding on surrounding farmland is controlled, electricity for new industries and it is helping Egypt to develop.
The negative impacts include:
High set up cost of building the dam, irrigated farmland suffers from salination, no fertile salt moves down river, land lost from the formation of Lake Nasser, evaporation from Lake Nasser is very high, water-borne diseases such as Bilharzia increase, silt builds up in Lake Nasser and farmland fertility is affected because the natural flooding is stopped.
Intermediate technology is also known as APPROPRIATE TECHNOLOGY - technology basic enough for people to know how to use them. Top down schemes are expensive, government schemes run by professionals. Bottom up schemes are run by NGO's (non government organisations) and meet the needs of local people, they are simple and easy to understand so can be fixed by locals if they break.
Old Zhimkhana is a slum on a disused railway station with no safe water or toilets.
WaterAid (NGO) constructed 6 tube wells and 2 new sanitation blocks.
- People are no longer continually ill,
- They can run facilities themselves,
- Moving out of poverty
Women would have to walk long distances to get water, they now have safe water for drinking, personal hygiene, cooking and washing. One problem of small schemes is that a huge number of people suffer from HIV/AIDS and are too ill to operate them.
Sustainable management of water in the UK - managing water for your use today but also managing water for future generations.
Small scale - showers instead of baths, share bath water, recycle bath water, water metre, don't always flush the toilet.
Large scale - manage reservoirs sensibly, adopt a thorough maintenance of leaking pipes.
Water quality is destroyed though - household waste, pesticides, animal and industrial waste and salt run-off from roads.