The water cycle and water insecurity - What are the processes operating within the hydrological cycle from global to local scale? Flashcards
Why is the global hydrological cycle a closed system?
It is a closed system of linked processes so there are no external inputs or outputs. For this reason, the amount of global water is finite and constant. The only thing that does change is the state in which the water exists (liquid, vapour or ice). The proportion of global water held in each state vary over time with changes in climate.
Where does the power that drives the global hydrological cycle come from?
The power that drives the global hydrological cycle comes from two sources:
1 solar energy: in the form of heat
2 gravitational energy: causes rivers to flow downhill and precipitation to fall to the ground
Name a climate change that would alter the proportion of water held in different states.
Global warming
What are stores?
Stores are ‘reservoirs’ where water is held.
What are the four main stores?
There are four main stores: (1) the oceans, (2) glaciers and ice sheets (cryosphere), (3) surface runoff and (4) the atmosphere.
What does surface runoff consist of?
Surface runoff consists of rivers and lakes, as well as groundwater.
What percentage of all the global freshwater does the cryosphere account for?
Of these freshwater stores, the cryosphere is the largest, accounting for 60% of all the global freshwater.
What percentage of groundwater does the cryosphere account for?
30%
Less than what percentage of groundwater is stored in the biosphere (vegetation and soil moisture)?
Less than 1% is stored in the biosphere (vegetation and soil moisture).
What are flows?
Flows are the transfers of water from one store to another.
What are the four main flows?
There are four main flows: precipitation, evaporation, transpiration and vapour transport.
What are fluxes?
Fluxes are the rates of flow between stores.
Where do the greatest fluxes occur?
The greatest fluxes occur over the oceans.
What is surface runoff?
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What is groundwater?
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What does the global water budget take into account?
The global water budget takes into account all the water that is held in the stores and flows of the global hydrological cycle.
What percentage of all the water that is held in the stores and flows of the global hydrological cycle is freshwater?
2.5%
What percentage of all the freshwater that is held in the stores and flows of the global hydrological cycle is ‘easily accessible surface freshwater’?
1%
What percentage of all the water that is held in the stores and flows of the global hydrological cycle is locked up in glaciers and ice sheets?
Nearly 70% is locked up in glaciers and ice sheets.
What is residence time?
This is the average time a molecule of water will spend in one of the stores. Residence times vary from 10 days in the atmosphere to 3,600 years in the oceans and 15,000 years in an ice cap.
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What two water stores are non-renewable?
It has been claimed that two water stores fossil water and the cryosphere are non-renewable. The latter is to be questioned because come another glacial period, more water will once again become locked in glaciers and ice sheets.
What are the main stores of easily accessible surface freshwater?
Ice caps & glaciers (69%)
Groundwater (30%)
What is a drainage basin?
The drainage basin is a subsystem within the global hydrological cycle. It is an open system with external inputs and outputs. Since those inputs vary over time, so does the amount of water in the drainage basin.
What is the main input in the drainage basin?
The main input is precipitation, which can vary in a number of different ways.
What characteristics of precipitation can have a significant impact on the drainage cycle/
- Form: rain, snow or hail. Clearly, with snow, entry of water into the drainage system will be delayed.
- Amount: this will affect the amount of water in the drainage basin and fluxes within it.
- Intensity: the greater the intensity, the greater the likelihood of flooding.
- Seasonality: this is likely to result in the drainage basin system operating at different flow levels at different times of the year.
- Distribution: this is significant in very large basins, such as the Nile and the Ganges, where tributaries start in different climate zones.
How does solar energy affect the drainage basin system?
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What characteristics of precipitation can have a significant impact on the drainage cycle?
- Form: rain, snow or hail. Clearly, with snow, entry of water into the drainage system will be delayed.
- Amount: this will affect the amount of water in the drainage basin and fluxes within it.
- Intensity: the greater the intensity, the greater the likelihood of flooding.
- Seasonality: this is likely to result in the drainage basin system operating at different flow levels at different times of the year.
- Distribution: this is significant in very large basins, such as the Nile and the Ganges, where tributaries start in different climate zones.
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