Water and carbon cycles
Distribution of global water stores:
Global water store approx . % of total stored water
Hydrosphere 96.5%
Atmosphere 0.001%
Cryosphere 1.7%
Lithosphere 1.7%
Transfers that change the size (magnitude) of the stores:
- Evaporation = the process whereby liquid water changes into a gas when it absorbs heat
energy. The remaining 10% comes from plant transpiration.
- Condensation = the process whereby the gaseous water vapour changes back into liquid
water within the atmospheric water store.
- Cloud formation = clouds form when water molecules aggregate (join up together).
- Precipitation = generally, precipitation occurs when the water molecules within a cloud
combine and become too big. This process is called coalescence.
Precipitation rates vary globally and over time. Rain doesn't fall in the same quantity in any place
around the world.
These are a range of reasons for differing rainfall patterns:
● Desert areas (most lie between 15° and 35° north and south of the equator) have limited
rainfall as they receive sinking, dry air from high pressure systems.
● Large continental interiors tend to be dry because of their distance from moisture sources and
many clouds lose moisture before they can reach the centre of large continents. Central North
America is an example of this.
● Polar areas are dry because cold air cannot hold as much moisture as warm air so
precipitation can’t occur so often.
● Areas near the equator receive high rainfall amounts because constant solar heating
produces intense heating, large-scale evaporation, moist rising air that cools with altitude and
forms convectional rainfall. In addition, air masses converge here which results in heavy
rainfall.
● Mid-latitudes may experience convectional rainfall and polar and sub-tropical air masses meet
here too which causes frontal (or depressional) precipitation. This is when a warm, moist
air mass cools as it is forced to slide up over a colder, denser mass of air.
● Mountain ranges near water sources can receive high levels of precipitation because of uplift.
Precipitation occurs when clouds rise to go over mountains and the air cools which
encourages the water molecules to join and then precipitation occurs. Known as relief, or
orographic precipitation, this accounts for many uplands receiving higher precipitation than
similarly-located lowlands. This can also result in a sharp reduction in rainfall in regions
behind (downwind of) the mountains. This phenomenon is commonly known as the
rainshadow effect.
, Cryospheric processes:
These are processes involving ice sheets and glaciers.
Past events and their impact on cryospheric processes:
- The last advance (60,000-20,000 BCE) led to an increase in glacial accumulation (snowfall
and increased ice coverage providing extra snow to glaciers and ice sheets) so the global
cryospheric store was considerably larger at this point.
Future events and their impact on cryospheric processes:
- The accumulation of glaciers and ice sheets (avalanches and snowfall) can vary depending
upon global climate change. Recent warming of global climate has reduced accumulation and
increased ablation (output) levels.
- Large volumes of summer meltwater and a reduction in winter accumulation has led to lower
storage levels in global ice sheets and glaciers.
- Hill slope changes will occur also as individual glaciers will melt completely, depositing their
encased material as moraines.
Drainage basins as open systems
A drainage basin is the area of land which is drained by a river and its tributaries. This area of land is
known as the catchment area.
Characteristics of a drainage basin:
- Watershed = the boundary of a drainage basin, usually a mountain range.
- Source = the start of a river within a basin.
- Mouth = where the river meets the sea.
- Tributary = a smaller stream which feeds into the main river.
- Confluence = the point at which two rivers meet.
Inputs and outputs:
One primary input = precipitation. This may vary according to the quantity, duration, intensity and
distribution over the year.
Outputs:
- Runoff - rivers entering the sea at the mouth.
- Evaporation - water warmed up by the sun is transferred from a liquid on the ground to a gas
in the atmosphere.
- Transpiration - water loss from vegetation into the atmosphere.
Evapotranspiration refers to the combination of evaporation and transpiration.
Stores: surface or underground repositories of significant quantities of water that may regulate the
rate at which input feeds through to the output.
● Lake storage: water can either travel overland or via the river channel or precipitation can fall
directly into a lake where it will be stored. Some water is released via a small outlet from the
lake and some can be evaporated into the atmosphere.
Distribution of global water stores:
Global water store approx . % of total stored water
Hydrosphere 96.5%
Atmosphere 0.001%
Cryosphere 1.7%
Lithosphere 1.7%
Transfers that change the size (magnitude) of the stores:
- Evaporation = the process whereby liquid water changes into a gas when it absorbs heat
energy. The remaining 10% comes from plant transpiration.
- Condensation = the process whereby the gaseous water vapour changes back into liquid
water within the atmospheric water store.
- Cloud formation = clouds form when water molecules aggregate (join up together).
- Precipitation = generally, precipitation occurs when the water molecules within a cloud
combine and become too big. This process is called coalescence.
Precipitation rates vary globally and over time. Rain doesn't fall in the same quantity in any place
around the world.
These are a range of reasons for differing rainfall patterns:
● Desert areas (most lie between 15° and 35° north and south of the equator) have limited
rainfall as they receive sinking, dry air from high pressure systems.
● Large continental interiors tend to be dry because of their distance from moisture sources and
many clouds lose moisture before they can reach the centre of large continents. Central North
America is an example of this.
● Polar areas are dry because cold air cannot hold as much moisture as warm air so
precipitation can’t occur so often.
● Areas near the equator receive high rainfall amounts because constant solar heating
produces intense heating, large-scale evaporation, moist rising air that cools with altitude and
forms convectional rainfall. In addition, air masses converge here which results in heavy
rainfall.
● Mid-latitudes may experience convectional rainfall and polar and sub-tropical air masses meet
here too which causes frontal (or depressional) precipitation. This is when a warm, moist
air mass cools as it is forced to slide up over a colder, denser mass of air.
● Mountain ranges near water sources can receive high levels of precipitation because of uplift.
Precipitation occurs when clouds rise to go over mountains and the air cools which
encourages the water molecules to join and then precipitation occurs. Known as relief, or
orographic precipitation, this accounts for many uplands receiving higher precipitation than
similarly-located lowlands. This can also result in a sharp reduction in rainfall in regions
behind (downwind of) the mountains. This phenomenon is commonly known as the
rainshadow effect.
, Cryospheric processes:
These are processes involving ice sheets and glaciers.
Past events and their impact on cryospheric processes:
- The last advance (60,000-20,000 BCE) led to an increase in glacial accumulation (snowfall
and increased ice coverage providing extra snow to glaciers and ice sheets) so the global
cryospheric store was considerably larger at this point.
Future events and their impact on cryospheric processes:
- The accumulation of glaciers and ice sheets (avalanches and snowfall) can vary depending
upon global climate change. Recent warming of global climate has reduced accumulation and
increased ablation (output) levels.
- Large volumes of summer meltwater and a reduction in winter accumulation has led to lower
storage levels in global ice sheets and glaciers.
- Hill slope changes will occur also as individual glaciers will melt completely, depositing their
encased material as moraines.
Drainage basins as open systems
A drainage basin is the area of land which is drained by a river and its tributaries. This area of land is
known as the catchment area.
Characteristics of a drainage basin:
- Watershed = the boundary of a drainage basin, usually a mountain range.
- Source = the start of a river within a basin.
- Mouth = where the river meets the sea.
- Tributary = a smaller stream which feeds into the main river.
- Confluence = the point at which two rivers meet.
Inputs and outputs:
One primary input = precipitation. This may vary according to the quantity, duration, intensity and
distribution over the year.
Outputs:
- Runoff - rivers entering the sea at the mouth.
- Evaporation - water warmed up by the sun is transferred from a liquid on the ground to a gas
in the atmosphere.
- Transpiration - water loss from vegetation into the atmosphere.
Evapotranspiration refers to the combination of evaporation and transpiration.
Stores: surface or underground repositories of significant quantities of water that may regulate the
rate at which input feeds through to the output.
● Lake storage: water can either travel overland or via the river channel or precipitation can fall
directly into a lake where it will be stored. Some water is released via a small outlet from the
lake and some can be evaporated into the atmosphere.
