Chapter 4 (Water 2)

• Hydrological cycle

  refers to a sequence of processes that leads to water being continuously and naturally renewed. It can also start at any stage.
• Precipitation : When water comes down as

  • rain
  • snow
  • hail
• Surface runoff :

  Where water flows from higher to lower elevation on the surface. It flows into the nearest rivers and streams
• Water may infiltrate the soil into the ground and be absorbed by plaints or percolate to lower levels of the soil and be stored as groundwater
• Evaporation

  it occurs when the sun's heat causes water to evaporate as it changes to water vapor
• Transpiration

  occurs when plants give out water vapor through their leaves
• Condensation

  Occurs when water vapor cools as it rises and turns into cloud droplets, As droplets combine and become bigger, clouds form
• Hydrological cycle

  Human activities can affect the hydrological cycle, leading to negative impacts

  EXAMPLE

  Deforestation can lead to less transpiration as well as less seeping of water into the ground. This may lead to more surface runoff and a higher occurrence of floods in an area as the water channels are unable to handle a high amount of runoff
• Water budget

  -> The amount of water flowing in and out of a catchment area, as well as the water available (Input and out put)

  • Input : Processes that contribute water into a catchment area

  e.g precipitation

  • Outputs : Processes that reduce the amount of water.

  e.g Evaporation and transpiration

  • The change in the amount of water stored in a water catchment when there are changes in the input and output are known as NET CHANGES.
• Net changes

  IF input and output same : water level remain the same

  IF input more than output : water surplus, the water catchment will be unable to hold the amount of water lead to floods

  IF output more than input : water deficit, not enough water in the water catchment will lead to water shortages and droughts
• variation of precipitation

  too much = Flood. overflow of large amounts of water on normally dry land. 2 types of floods. river floods and flash floods

  too little = droughts
• Flash floods

  • unusually high rainfall in a short period of time
  • occurs in dry areas with insufficient soil or vegetation to allow rainfall to infiltrate the ground
  • Most of the rainfall becomes surface runoff that quickly floods low-lying areas
• River floods

  • Sustained heavy rainfall, or when snow and ice turn in to meltwater.
  • Melt water enters streams which flow into rivers
  • Water levels in the river rise rapidly and overflow, flooding the surrounding land
• Droughts

  • long periods of little to no rainfall in an area.
  • May last for months or several years
  • Insufficient water to replenish the amount used for human activities or lost though evaporation and transpiration
  • May lead to water stores such as reservoirs and groundwater drying up
• Water and the Ecosystem

  • Ecosystem -> a community of plants and animals that interact with one another in an environment
  • River ecosystems are found along bodies of water such as rivers and lakes
  • Precipitation provides a regular supply of water to rivers, allowing organisms living in these ecosystems to survive
• Food chain

  • At the bottom of the food chain are aquatic plants known as phytoplankton, which convert energy from sunlight through photosynthesis and release oxygen into the water.
  • Each creature feeds a predator above it on the food chain, with humans being at the top of the food chain
  • If the supply of water to the river is decreased due to insufficient rainfall, the ecosystem and food chains may be affected
• How people use water

  • Domestic
  • Recreational
  • Agricultural
  • Industrial
• Domestic uses of water

  • examples : Car washing, showering
  • Bathing cooking and toilet flushing account for highest percentages of domestic water usage in Singapore
  • The amount of water used per household varies across countries and communities. People from wealthier countries would tend to have higher water footprints
• Recreational use

  • Leisurely activities
  • Some recreational activities involve using water bodies as part of the activity, such as kayaking, fishing, sailing
  • These activities are highly dependent on water condition and water quality
• Industrial use

  • Water is important for many industries to cool equipment in factories and power plants due to high amounts of heat generated
  • Dams can generate electricity using water
  • Water can be used as a cleaning agent in wafer fabrication
• Agricultural use

  • account for the largest global usage of water
  • Water used to grow crops and rear animals
  • However, different crops and animals require different amounts of water. Some are more water-intensive than others
• Pollution

  • refers to the introduction of harmful substances into the physical environment
  • Includes water, land, air and noise pollution
  • Water pollution occurs when people throw rubbish into water channels such as drains and when factories dump toxic waste into the water
  • Water pollution is more likely to occur in countries that lack proper water treatment facilities or have landfills that are filled up, leading to wastes being leaked
• Impact of water pollution

  • Leads to lower quality, leading to a reduction in the amount of clean and usable water
• Eutrophication

  • It is a threat to aquatic systems when pollutants such as pesticides may kill aquatic plants and poison animals.
  • Excess fertilizers used in agriculture can also wash into rivers. causing algae to grow repandly, This is known as algae bloom.
  • The increase in the number of algae as well as decomposition by bacteria when it dies causes a lot of oxygen in the water to be used up. This results in less oxygen in the water, leading to fish and other aquatic creatures dying