The hydrological cycle
Hydrosphere: Consists of all the water on the planet.
Hydrological cycle: Closed system- none is added or lost from the system. The stores of water are linked by processes which transfer water into and out of them. Stores: Oceans, polar ice and glaciers, groundwater, lakes, soils, atmosphere, rivers, living things.
- Surface flow: Rain falls on the ground and flows on the surface into rivers and lakes.
- Through flow: Rain water is soaked into the soil (infiltration) and slowly flows back to the rivers.
- Groundwater flow: Rain water is soaked into rocks below the soil. It moves slowly through cracks and joints or airspaces (pores).
- Precipitation: Rain or snow
- Infiltration: movement of water into the soil from the surface.
Water can change state by:
- Evaporation: Liquid changes to vapour
- Condensation: Vapour turns into liquid.
- Melting or freezing.
Role of the biosphere and lithosphere
- Trees intercept precipitation and over half is evaporated and transpired without reaching the surface.
- If storm or rainfall is very heavy, or it goes on for a long time, precipitation drips from leaves and stems and slowly makes its way into the river system.
- Precipitation infiltrates the soil where it flows down the slope as throughflow, or if the underlying rock is permeable, into the ground to be stored as ground water.
- Only after many hours the water is released into the river basin.
Climate change and the hydrological cycle
Global warming and climate change will effect rainfall, evapotranspiration and water availability.
Places allready suffering from water shortages will likely experience lower rainfall.
The dry areas of developing countries will be the hardest hit.
Wet areas like the UK will get wetter.
Unreliable water supply impacts
Here are the three main reasons why water supplies may be unreliable...
- There may be specific wet and dry seasons - In the Sahel in Africa, they have a long dry period which causes the ground to become hard. In the short wet period the Sahel gets, there is a lot of water run-off so little water is stored.
- There may be weather cycles where an area may get several dry years followed by several wet years - recently in the Sahel, they have been experiencing several years of droughts, leading to serious food shortages.
- Global warming and a continuing rise in temperatures - Dry places like the Sahel will get drier, and wet places like here in the UK will get wetter.
South- West USA
- South-west USA is a very arid area with a lot of dependency on the Colorado River which is their main source of water, including the irrigation of crops
- Climate Change poses the threat of making the area even drier. Las Vegas experienced drought years in 2002, 2004 and 2007.
- This threat of climate change will lead to restrictions being enforced on taking water from the Colorado River. This will have a knock-on effect of people having less water for irrigation, meaning fewer crops and artificially created green areas.
- The lack of water will also create problems for the rapidly increasing population of the area. Arizona had a population increase of 25% between 2000 and 2010.
Climate change and Asia
Countries in Asia, such as China, India and Vietnam, depend greatly on their water from the melting glaciers in the Himalayas.
The Long-term impacts of climate change could result in all the Himalayan glaciers melting leading to severely reduced water supplies.
The Short-term impacts of climate change could result in an increase in glacial melt in the Himalayas leading to seasonal stress on agriculture for example.
Threats to to the hydrologiccal cycle
River pollution causes:
- Untreated sewage pumped into rivers can lead to serious diseases such as Cholera and typhoid.
- Intensive agriculture which releases fertilisers, pesticides and herbicides into the local water systems can poison wildlife and affect water quality.
- Waste chemicals which are leaked from factories can poison wildlife and affect water quality
- Plastic bags and other non-biodegradable waste can kill wildlife, clog up water ways and affect water quality.
Managing river pollution:
- Sewage is treated before it can be pumped into rivers
- Farmers and land-owners regulate their use of fertilisers and chemicals to reduce pollution and damage
- Factories dispose of their chemical waste before returning water to the river.
- In the UK, the Environment Agency imposes heavy fines on any factory which releases chemical waste into the environment.
- Plastic and all other recycable waste is sent to recycling centres to be recycled rather than being dumped in rivers.
River Rhine (Europe)
1. Many types of industries have established 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 the detergents industries also dump their waste into the river. Although most of these emissions are properly authorised, some emissions are not and there is always the risk of accidental spill or leaks.
2. Households dispose of a variety of waste products: soap, detergents, leftovers and sewage. People often throw things directly into the river, from pieces of paper to rusting bed frames and old bicycles.
3. Many agriculture 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.
- Metals pollute river.
- Public health would be effected if the water was not purified.
- High salinity of the water gives it an unpleasant taste and erodes the pipelines.
Human disruption of water supply
How people intervene in the water cycle:
1. CLOUD SEEDING: making it rain
2. DEFORESTATION: Decreased interception increased flooding
3. URBANISATION: Increased impermeable surfaces
4. OVERABSTRACTION: taking too much water from rivers and lakes
5. BUILDING DAMS AND RESERVOIRS
6. GLOBAL WARMING: melting glaciers
Thames valley England
- Dramatic decrease in river flow
- Tributaries dried up
- Ecosystem damaged Droughts and increased demand from more homes
- Increased use of groundwater supplies
- Falling water table so the store of water is not used sustainably.
- Most water companies now have strict policies CAMS (Catchment Abstraction Management Strategies) for managing water levels.
Adds a new store to the hydrological cycle
- Loss of land – drowns villages, farmland
- Disease – stagnant water mosquitoes
- Vegetation drowned releases methane = greenhouse gas
- Water supply
- Recreation – fishing, sailing, walking, wildlife
- Fewer trees = less Evapotranspiration.
- Less green water recycled = less rain.
- Soil left exposed to the sun and rain -Less nutrients in the soil
- Raindrops wash out the finer soil, leaving coarse, heavy surface.
- Less interception - greater flood risk
Large scale, developed world
Cholorado river USA
- Reduces flooding that would normally occur in the summer, and reduces drought that would normally occur in the winter
- Electricity is produced by the dam for local towns, farms and factories
- Water is stored behind the dam which can be used for irrigation and for supplying growing cities such as Las Vegas.
- There is year-round supply of clean water for US cities.
- Land is lost to flooding when making the dams.
- Sediment has built up behind the dams which affects the workings of the Hydroelectric Power (HEP) generation.
- Less sediment flowing down the river has disrupted the habitat for native fish.
- Also, the lack of sediment means sandbanks have shrunk which is also impacting animals and their habitats.
- Less water downstream in Mexico
Large scale, developing world
Three gorges dam, China
- Reduced risk of flooding for homes, farms and factories along the Yangtze River
- Water stored behind the dam is available for irrigation
- Hydroelectric power (HEP) is generated by turbines in the dam. It's the world's largest capacity HEP station. The electricity it produces means China saves 31 million tonnes of coal each year and thier overall greenhouse gas emissions has reduced
- The river is deeper and more navigable for ships, so it has improved transport and trading in China
- Good farmland has been lost because of the dam.
- Over 1 .3 million people were forced to move their homes as towns and villages disappeared under water.
- Important cultural and archaeological sites were lost.
- There is an increased risk of landslides in some places.
- The project was very expensive, $US 22.5 billion, but some people estimate the actual cost to be as high as $US 50bn.
- Sediment is building up behind the dam. There is no sediment to maintain river banks resulting in downstream areas becoming more at risk to flooding.
- Important wetland areas have been destroyed.
Small scale intermediate technology
In the developing world, you are more likely to find small scale, intermediate technology solutions to any unreliable water problems. These solutions are relatively cheap to build and maintain, cover small areas, are organised by the local people in conjunction with charities and local organisations, and help local people access clean water and increase water storage safely.
Wells - Wells are dug to reach underground water supplies. They are lined with concrete and have a concrete lid to prevent pollution by sewage.
Hand pumps - A more efficient way of reaching underground water where there is less chance of water becoming contaminated.
Rain barrel - Water barrels collect rainwater from gutters and roofs can be stored and used in times of droughts. This is called water harvesting. The water stays clean in the covered barrel.