Water

• What percent of water in our planet is stored in oceans and seas?

  97%
• What are the Earth's five subsystems?

  Atmosphere: the blanket of air that surrounds the Earth's surface

  Cryosphere: all forms of frozen water

  Lithosphere: the rock shell of the earths surface

  Biosphere: zone of all living things

  Hydrosphere: all of the water existing on or within the solid surface of the Earth
• Is the hydrological system a closed or open system?

  A closed system, therefore the amount of global water is finite and constant. The only thing that does change is the state in which the water exists
• What are the four main stores ('reservoirs' where water is held) for water?

  Oceanic water

  Cryospheric water

  Terrestrial water

  Atmospheric water
• Oceanic water


  The five oceanic bodies of water and smaller seas cover 72% of the Earth's surface. The Pacific Ocean is the largest.
• Cryospheric water


  Composed of sea ice, ice caps, ice sheets, glaciers and permafrost. Many are in high altitude and high latitude areas e.g ice sheets in Antarctica, or ice caps like the Himalayas
• Terrestrial water


  Rivers such as the Amazon, lakes (Canada and Finland have the most), wetlands (which are found in every continent apart from Antarctica), groundwater, soil water and biological water
• Atmospheric water


  The most common form is water vapour. It's important as it absorbs and reflects incoming solar radiation. Warm air holds more water vapour than cold air. A small increase in water vapour will lead to an increase in atmospheric temperatures (positive feedback)
• How are freshwater stores divided into the different stores?

  Cryosphere is the largest, holding 69% of global fresh water

  Groundwater holds 30%

  Less than 1% is stored in the biosphere (vegetation and soil moisture)
• What are the four main flows? (Transfers of water from one store to another)

  Precipitation, evaporation, transpiration and vapour transport
• What are fluxes?


  Rates of flow between stores. The greatest fluxes occurs over the oceans
• How is the hydrological cycle powered?

  1. Solar energy - heated by the sun, water in the surface evaporated into the atmosphere. Water is also drawn from the soil by plants and evaporated by evapotranspiration. Water is condensed forming clouds, leading to precipitation = water is returned to the land

  2. Gravitational potential energy - on land, GPE is converted to kinetic energy as water moves through the system by plant interception, or over land via runoff. Water also flows through soil by the process of infiltration and through flow
• What is the global water budget?

  It takes into account all the water that is held in stores and flows of the global hydrological cycle. The most significant feature of the water budget is that only 2.5% of it is freshwater, the rest is in oceans.
• How much of the 2.5% of freshwater is 'easily accessible surface freshwater'?

  Only 1% is 'easily accessible fresh water'. Nearly 70% of fresh water is locked up in glaciers and ice sheets
• What is fossil water?

  Ancient, deep groundwater from pluvial (wetter) periods in the geological past
• What does the residence time for each store mean?

  The average time a molecule of water will spend in one of the stores.

  Water stored in the soil has a very low residence time

  Atmospheric water has the shortest residence time (approx 10 days)

  Ancient ground water/ fossil water has a long residence time

  Major ice sheets store water as ice for extremely long periods. Some Antarctic ice is over 800,000 years
• What is the link between residence times and level of water pollution?

  There is a very strong link between the two: stores with a slower turnover tend to be more easily polluted as the water is in situ for a longer length of time
• What is the drainage basin?

  It is a subsystem within the hydrological cycle and is an open system with external inputs and outputs. It is an area of land drained by a river and its tributaries.

  Drainage basins vary in size from that of a small local stream to a huge river like the Amazon.
• What are the main inputs to a drainage basin and why do they occur?

  Precipitation and condensation.

  1. When air temp is reduced to a dew point e.g warm air passes over a cold surface on a clear night, or when heat is radiated out into the atmosphere and the ground gets cooler, cooling the air above it

  2. Volume of air increases as it rises and expands but there is no addition in heat (adiabatic cooling)
• What are the three ways adiabatic cooling occurs? (Each resulting in precipitation)

  1. Orographic (relief) precipitation where air is forced to rise over hills and mountains

  2. Frontal precipitation where air masses of different temperatures and densities meet, the warm air rising over the cool sinking air

  3. Conventional precipitation where warm air rises from hot surfaces on a sunny day
• What factors affect the levels of precipitation?

  Rainfall amount

  Type of precipitation

  Distribution within basin

  Variability of rainfall

  Intensity of precipitation

  Seasonality
• What are the 8 flows?

  Interception

  Infiltration

  Percolation

  Throughflow

  Groundwater flow

  Direct run-off (direct overland flow)

  Saturated overland flow

  Channel flow
• What affects interception?


  1. It depends on the size of the leaves and this can also vary throughout the year depending on if the tree is deciduous or not.

  2. Meteorological conditions can also have a major impact. Wind speeds can increase interception loss

  3. The intensity and duration of rainfall plays a key factor too. As rainfall increases, the relative importance of interception losses will decrease as the tree canopies become saturated, so more excess water will reach the ground

  4. Agricultural crops make interception vary as interception rates increase with crop density
• What are the outputs of the hydrological cycle?

  Evaporation

  Transpiration

  Evapotranspiration

  Potential evapotranspiration (the amount of water loss that would happen if there was unlimited support of water in the soil for transpiration by vegetation)

  Discharge
• What physical factors affect outputs?

  1. Temperature - evaporation increases as temp increases

  2. Wind - increases the rate of evaporation by reducing the relative humidity, preventing saturation of the air

  3. Vegetation cover - transpiration increases with increased vegetation cover

  4. Soil moisture content - it determines the amount of water available for transpiration. It is dependent on soil and rock permeability
• What factors influence flows of water?

  1. Precipitation intensity - infiltration-excess overland flow will occur when rainfall intensity exceeds infiltration capacity

  2. Vegetation cover - roots help to break up soil, increasing the infiltration rate

  3. Soil and rock type - infiltration increases with permeability

  4. Water table depth - as water table rises during prolonged rainfall, soil becomes saturated, reducing infiltration

  5. Slope gradient - as gradient increases, more water will flow over the surface, reducing infiltration
• What is a water budget?

  An annual balance between precipitation, evapotranspiration and runoff. It is calculated using the formula P=E+R+/-S

  P=precipitation

  E=evapotranspiration

  R=runoff

  S=storage over a period of time, usually one year
• What is a river regime?

  An annual variation in the discharge or flow of a river at a particular point, and is usually measured in cumecs
• What influences the character of a river regime?

  Geology - permeable vs impermeable rock

  Precipitation amounts and seasonality

  Position of measuring station in relation to the size and shape of the basin

  Human factors - reservoirs or abstraction of water

  Evaporation in summer

  Temperatures - Melting snow = spring maximum
• What are the main features of a hydrograph?

  Rising limb - once the rainfall starts, the discharge begins to rise

  Peak discharge - reached sometime after the peak rainfall because the water takes time to move over and through the ground

  Lag time - the interval between peak rainfall and peak discharge

  Falling limb - once the input of rainwater into the river starts to decrease, so does the discharge

  Base flow - eventually, the river's discharge returns to its normal level
• Bankfull 


  amount of water in a river before it floods
• Yukon river regime


  tundra

  high seasonal variation

  summer = snowmelt (high temps causes evaporation), winter = frozen
• Amazon river regime

  tropical rainforest

  high evapotranspiration

  wet vs dry season (rainfall in every month)

  moderate variability
• Murray Darling river regime


  wet vs dry season

  ITCZ

  used for irrigation and drinking in largest cities

  most of basin in rain shadow
• Storm hydrographs


  discharge during and after a storm or at a given point over a period of time

  shows basin response to storm e.g flashy vs flat/slow
• Sustainable Drainage Systems

  soak-aways

  green roofs

  rainwater harvesting
• water budget

  balance between inputs and outputs
• flashy hydrographs

  • impermeable rock
  • clay soil
  • prolonged rainfall and capacity to carry (antecedent condition)
  • deciduous plants - less interception in winter
  • deforestation
  • urbanisation - less permeable
• river regimes - what impacts them

  climate - seasonal distribution of rainfall, determines evapotranspiration rates

  geology - aquifers with porous rock (water released slowly).

  soils - deep and healthy soil stores more water
• what does river regime indicate

  annual variation of discharge of a river