what is the hydrological cycle? topic 4: water world

What is the hydrological cycle?

Topic 4: Water World

• The hydrological cycle or water cycle is the movement of water between its different forms; gas (water vapour), liquid and solid (ice) forms.


Processes in the hydrological cycle:Inputs

OutputsStores

Flows/transfers


Water scarcity


So far, freshwater is not scarce on a global scale. However, many parts of the word are now experiencing water stress.

Write down what you understand the term “water stress” to mean

Water scarcity comes in two types:

Physical scarcity – shortages occur when demand exceeds supply. I.e. There is not enough good quality water available for everyone to have the amount they need

Economic Scarcity – when people cannot afford the water even if it is readily available.


Water stress


So far, freshwater is not scarce on a global scale. However, many parts of the word are now experiencing water stress.

Water stress occurs when the demand for water exceeds the amount available during a certain period, or when it is not good enough quality to use.


Causes of decline in water availability and water quality


Industrial development The growth of manufacturing industries is based on water supply especially steel and paper. They also rely on rivers and oceans to dump waste.

Decline in water availability and

quality

Population growth World population grew from 2.5 to 6.2 billion between 1950 and 2000. 7 billion people are estimated to have insufficient water by 2050

Agriculture Demands Rising population increases the demand for food and water needed for farming. The area of irrigated land doubled during the 20th century. Water shortages may threaten future food supplies.

UrbanisationBy 2025 nearly 60% of the worlds population will live in urban areas. The water and sanitation supply won’t be able to cope.

Energy Developing countries have vast untapped HEP resources. But storing water in reservoirs increases the amount of water lost through evaporation and water related diseases.

Climate ChangeGlobal warming and climate change will affect rainfall and water availability . Areas already experiencing shortages are likely to experience lower rainfalls. Dry areas will be hardest hit.


Living with water shortage

What case study did we use?


Sahel: Case study of an area with a poor supply of water

• The Sahel is a part of Africa which has a poor supply of water. There is also an Economic Scarcity of water as the area is very poor and so cannot afford to store or transfer the water to the most needed places.

• The area suffers from Desertification (the spreading of deserts) due to the lack of rainfall and human activities such as overgrazing, which leaves the soil open to erosion.

Causes of desertification


How humans affect water quality

Topic 4: Water WorldTopic 4: Water WorldTopic 4: Water World


Minamata disease in Japan- caused by mercury poisoning. In the late 1950s tonnes of toxic mercury was released into Minamata Bay in Japan which affected fish and shellfish. These were then consumed by humans which lead to severe mercury poisoning and, in many cases, death.

Human excrement- Cholera bacteria spread easily in river water when contaminated with human waste.

Plastic BagsBlock waterways and sewers which worsens flooding problems particularly in Bangladesh during monsoon season. Plastic bags also get trapped by vegetation along river banks, providing pools of still warm water where malaria carrying mosquitoes will breed.

Human interference to the hydrological cycle


Human interference with the Water Cycle

Humans can have a negative impact on the water cycle through deforestation and overabstraction.

Overabstraction- means too much water is being taken from the river, lake or other water source.

Deforestation has three impacts on the water cycle:1.Interception is reduced as there are fewer trees to “catch” the water.

This means that the water will travel more quickly into the river= increases chance of the river flooding.

2.The tree roots no longer hold the soil together, so it is more easily eroded by the rainfall and washed into the river. This leads to sedimentation (the river filling with silt/soil) and therefore flooding.

3.Less evapotranspiration will take place and this can lead to less rainfall and desertification. Topic 4: Water World

Large Scale solution to water management


Costs (problems) Benefits

Loss of land as it is flooded by the reservoir Less flood risk as flood peaks are smoothed out.

Shrinking sandbanks mean some animals lose habitat. Create reservoirs which providesregular all-year water supplied for cities like Las Vegas

Rates of silt transportation has reduced and made the water cooler downstream as silt heats up in sunlight. This has lead to 4 species of fish being lost.Very expensive! Local people have little input or say on how it is managed.

Large-scale water management- The Colorado River and the Hoover Dam

• The Colorado River feeds the need of 7 US states and Mexico. Water management techniques have mean that US cities and farms have access to reliable water supplies all year round.

• The Hoover Dam holds an enormous amount of water for desert cities like Las Vegas. Water is piped along man-made constructions called aqueducts.


Small-scale solutions to water management


Small-scale water management: Rainwater harvesting (pumpkin tanks) and Afridev hand pump

Afridev Hand pump- Tanzania, East Africa.Facts:• Life expectancy is 46• 70% rural population

and 30% of urban population have no access to safe, clean water

• Diarrhoea accounts for at least 20% of infant deaths


WaterAid brings intermediate technology to communities that need clean water by helping villages construct wells to access safe, clean underground water. The pumps are dug 24 metres deep and are fitted with an Afridev handpump. Local people are trained to manage the pump in case it breaks down giving them ownership of the scheme.

Rainwater harvesting (Pumpkin tank)

Appropriate or intermediate Technology


• Development schemes that meet the needs of local people and the environment in which they live.


what is the hydrological cycle? topic 4: water world

Documents

water world slide

water supply

water cycle

water availability

water shortages

movement of water

insufficient water

water scarcity topic