Geography Physical - Water Cycle

• Hydrological cycle


  A system made up of 3 parts: stores - places where water is held, fluxes - measurement of the rate of flow between stores, processes - physical factors which drive the fluxes of water between stores
• The global hydrological cycle is a closed system - no water is added/removed from the global budget
• Drivers of the hydrological cycle


  Solar energy and gravitational potential energy
• States of water


  • Solid
  • Liquid
  • Gas
• Main stores of water


  • Oceans
  • Ice caps and glaciers
  • Groundwater
  • Rivers and lakes
• Blue water


  Rivers, streams, etc.
• Green water


  Water in vegetation
• Residence time


  The average time a water molecule spends in a store
• Flows


  The transfer of water from one store to another
• Processes that achieve flows


  • Precipitation-condensation
  • Evaporation
  • Transpiration
  • Infiltration
  • Percolation
  • Drainage
• Drainage basin


  The area of land drained by a river and its tributaries
• Watershed


  The boundary of a drainage basin
• Drainage basin water cycle


  A subsystem within the hydrological cycle
• Inputs and outputs of a drainage basin


  • Precipitation
  • Interception and infiltration
  • Evaporation
• Precipitation


  For rain, snow or hail to form, certain conditions must be met: air is cooled to saturation point, condensation nuclei (e.g. dust) facilitate droplet growth in clouds, temperature below dew point
• Orographic rainfall


  • When air is forced to rise over a mountain, it cools and condenses, raining on one side (the windward side) while the other side (the leeward side) experiences a rain shadow
• Storm hydrograph


  Shows how a river's discharge varies over time, affected by types of flow, rainfall intensity, temperature, basin shape, geology, and antecedent conditions
• River regime


  The annual variation in discharge of a river, affected by drainage basin area, mean annual precipitation, altitude, geology, and land use
• Water budget


  The balance between inputs and outputs of water in a system
• Physical factors affecting the water cycle


  • Climate
  • Geology
  • Vegetation
• Human factors affecting the water cycle


  • Deforestation
  • Dam construction
  • Water abstraction
  • Urbanisation
  • Overpopulation
• Globalisation


  The interdependence within the global economy
• Types of drought


  • Meteorological
  • Hydrological
  • Agricultural
  • Socio-economic
• Climate change impacts


  • Increased precipitation in some regions leading to higher flood risk
  • Decreased precipitation in other areas leading to more droughts
  • Higher evaporation from reservoirs reducing water supplies
  • Reduced evaporation when temperatures are below freezing leading to more water stored in the cryosphere
• El Niño Southern Oscillation (ENSO)


  An irregular, periodic variation in winds and sea temperatures across the Pacific Ocean, with global impacts on weather patterns
• Impacts of flooding


  • Injuries/illnesses/deaths
  • Damage to properties
  • Impacts on livelihoods
  • Environmental impacts (e.g. plant/animal destruction, soil erosion, eutrophication)
• Causes of water surpluses


  • Intense precipitation over a short period
  • Sudden snow melt
  • Unusually heavy or prolonged rainfall
  • Monsoonal rainfall
  • Steep slopes
  • Permeable rocks
  • Size and shape of drainage basin
  • Human activities (e.g. channelisation, urbanisation, land use changes)
• Human influences on drought


  • Desertification
  • Deforestation
  • Over-abstraction of groundwater
  • Overcultivation
  • Climate change
  • Changes in land use
  • Dam and reservoir construction
• Impacts of droughts


  • Impacts on ecosystems (e.g. wetlands, rainforests)
  • Impacts on agriculture and food production
  • Impacts on water supplies and human settlements
• HUMAN INFLUENCES ON DROUGHT


  HUMAN ACTIVITIES can have a large role in contributing to droughts
• DESERTIFICATION


  • DEFORESTATION less vegetation leads to increased soil erosion
  • Less evapotranspiration
• OVER-ABSTRACTION


  • Groundwater stores reduced
• OVERCULTIVATION


  • Reduced soil fertility, soil exposed, increased soil erosion
• CLIMATE CHANGE


  • Higher global temperatures, increased evaporation, reduced condensation
• CHANGES IN LAND USE


  • Clearing, burning, ploughing, bereans so erosion
• DAMS & RESERVOIRS


  • Reduced channel flow downstream
• IMPACTS OF DROUGHTS


  • Droughts can have significant impacts on ecosystems
  • Wetlands
  • Rainforests
• Wetlands cover 5-8% of the Earth's land surface
• Wetlands are very important ecologically e.g. temporary water stores, recharge aquifers, habitats etc.
• Wetlands have been dredged and drained to create space for farmland