Physical Geography: Revision
Key knowledge
- On a local scale, the water and carbon cycles are open systems; on a
global scale, both are closed systems meaning a system that transfers
energy but not matter across its boundary
- Dynamic equilibrium is where there is a state of balance within a system
that is constantly changing
- Negative feedback loops take a system back to dynamic equilibrium
- Positive feedback loops take a system further from dynamic equilibrium
Global Distributions of water: Water Cycle
- Hydrosphere – all liquid water
- Cryosphere – all frozen water
- Lithosphere – upper mantle and crust
- Atmosphere – water vapour
- Aquifers: underground stores of water that are unevenly distributed on
a global scale
Shallow Groundwater Aquifers Up to 200 years
Deeper Fossil Aquifers (formed Up to 10,000 years
during wetter climatic periods)
Glaciers 20-100 years
Lakes 50-100 years
Seasonal snow cover and rivers 2-6 month
Soil water (temporary store) 1-2 months
The Inter-Tropical convergence Zone
- The global atmospheric circulation model is the main factor determining
cloud formation and rainfall
- Different zones of rising and falling air lead to precipitation through
convectional rainfall
- This creates a low pressure zone on the equator called the ITCZ which
has very heavy rainfall and is partially responsible for monsoons
- This zone moves during the seasons (North and South) as the position of
the sun changes
- Where the Ferrell and Hadley cells meet, unstable weather occurs and is
moved by the jet-stream, causing changeable weather in the UK
Changes to the Water Cycle over time – Natural Processes
- Seasonal changes: less precipitation and more evapotranspiration in
summer, less flows of water in winter as water freezes as ice; reduced
interception in winter as deciduous trees lose leaves
- Storm events: sudden increases in rainfall means flooding and
replenishment of some water stores (unlikely to have long-term effects)
, - Cryospheric processes: historically, glaciers and ice caps stored
significant proportions of fresh-water through the process of
accumulation; currently almost all glaciers are melting, making sea levels
rise – if all glaciers and ice caps melt, seal levels will rise by roughly 60m)
Changes to the Water Cycle over time – Human Impacts
- Farming practices: ploughing breaks up the surface, increasing
infiltration; arable farming (crops) increases interception and
evapotranspiration; pastoral farming (animals) trampling compacts the
soil, reducing infiltration and increasing runoff
- Irrigation: removes water from local rivers, decreasing flow
- Land use change: deforestation reduced interception and
evapotranspiration but infiltration increases as dead plant material in
forests usually prevents infiltration
- Water abstraction: water removed, reduces the volume of water in
surface stores – water abstraction increases in dry seasons as water is
needed for irrigation
Changes to the water cycle – Local
- Agriculture/ Farming
- Urbanisation – creation of roads and buildings with impermeable
surfaces, and these are likely to have drains: this would initially decrease
infiltration but drains will increase surface runoff, reducing lag-time and
increasing flood risk of local rivers
- Green roofs and SUDs use soil and grass to reduce impermeable
surfaces, decreasing the risk of urban flooding
The water Balance
- Used to express the process of water storage and transfer in a drainage
basin system
- Precipitation = total runoff + evapotranspiration +/- change in store
Soil Water Budget
- Shows the annual balance between inputs and outputs in the water
cycle and their impact on soil water storage/availability
- The water budget is also dependent on type, depth and permeability of
soil and bedrock
Key knowledge
- On a local scale, the water and carbon cycles are open systems; on a
global scale, both are closed systems meaning a system that transfers
energy but not matter across its boundary
- Dynamic equilibrium is where there is a state of balance within a system
that is constantly changing
- Negative feedback loops take a system back to dynamic equilibrium
- Positive feedback loops take a system further from dynamic equilibrium
Global Distributions of water: Water Cycle
- Hydrosphere – all liquid water
- Cryosphere – all frozen water
- Lithosphere – upper mantle and crust
- Atmosphere – water vapour
- Aquifers: underground stores of water that are unevenly distributed on
a global scale
Shallow Groundwater Aquifers Up to 200 years
Deeper Fossil Aquifers (formed Up to 10,000 years
during wetter climatic periods)
Glaciers 20-100 years
Lakes 50-100 years
Seasonal snow cover and rivers 2-6 month
Soil water (temporary store) 1-2 months
The Inter-Tropical convergence Zone
- The global atmospheric circulation model is the main factor determining
cloud formation and rainfall
- Different zones of rising and falling air lead to precipitation through
convectional rainfall
- This creates a low pressure zone on the equator called the ITCZ which
has very heavy rainfall and is partially responsible for monsoons
- This zone moves during the seasons (North and South) as the position of
the sun changes
- Where the Ferrell and Hadley cells meet, unstable weather occurs and is
moved by the jet-stream, causing changeable weather in the UK
Changes to the Water Cycle over time – Natural Processes
- Seasonal changes: less precipitation and more evapotranspiration in
summer, less flows of water in winter as water freezes as ice; reduced
interception in winter as deciduous trees lose leaves
- Storm events: sudden increases in rainfall means flooding and
replenishment of some water stores (unlikely to have long-term effects)
, - Cryospheric processes: historically, glaciers and ice caps stored
significant proportions of fresh-water through the process of
accumulation; currently almost all glaciers are melting, making sea levels
rise – if all glaciers and ice caps melt, seal levels will rise by roughly 60m)
Changes to the Water Cycle over time – Human Impacts
- Farming practices: ploughing breaks up the surface, increasing
infiltration; arable farming (crops) increases interception and
evapotranspiration; pastoral farming (animals) trampling compacts the
soil, reducing infiltration and increasing runoff
- Irrigation: removes water from local rivers, decreasing flow
- Land use change: deforestation reduced interception and
evapotranspiration but infiltration increases as dead plant material in
forests usually prevents infiltration
- Water abstraction: water removed, reduces the volume of water in
surface stores – water abstraction increases in dry seasons as water is
needed for irrigation
Changes to the water cycle – Local
- Agriculture/ Farming
- Urbanisation – creation of roads and buildings with impermeable
surfaces, and these are likely to have drains: this would initially decrease
infiltration but drains will increase surface runoff, reducing lag-time and
increasing flood risk of local rivers
- Green roofs and SUDs use soil and grass to reduce impermeable
surfaces, decreasing the risk of urban flooding
The water Balance
- Used to express the process of water storage and transfer in a drainage
basin system
- Precipitation = total runoff + evapotranspiration +/- change in store
Soil Water Budget
- Shows the annual balance between inputs and outputs in the water
cycle and their impact on soil water storage/availability
- The water budget is also dependent on type, depth and permeability of
soil and bedrock
