1.1: The drainage basin system
hydrological cycle: interaction between atmosphere, lithosphere and
biosphere
drainage basin system: open system which allows movement of
energy and mass through its borders
Outputs
evaporation: liquid into gas, most important in oceans.
- increases in warm, dry conditions and decreases in cold, calm
conditions.
- losses are greater in arid and semi-arid climates than in polar
regions.
- factors affecting rate:
● meteorological factors: temperature, humidity and wind
speed.
● water availability
● vegetation cover
● colour of surface
evapotranspiration: process by which water escapes from a living plant
(stomata or surface of leaf) and enters the atmosphere.
- represents most important aspect of water loss
- pure evaporative losses occur over ice, snow fields, rock slopes,
desert areas, water surfaces and bare soil.
- factors affecting rate:
● factors affecting evaporation
● plant adaptations: cacti reduce water loss.
potential evapotranspiration: difference lies in concept of moisture
availability; water loss that would occur if there was an unlimited supply
of water in soil for the use of vegetation.
river discharge: movement of water in channels.
- may enter river directly as precipitation or by surface runoff,
groundwater flow or throughflow.
, Stores
interception: water that is caught and stored by vegetation. increases
rate of infiltration. Three main components:
- vegetation storage: water retained by plant surfaces , later
evaporated away or absorbed by a plant - varies with plant type
- throughfall: water that either falls through gaps in vegetation or
drops from leaves
- stemflow: water that trickles along twigs and branches, and finally
down the trunk
less from grasses than from woodland - smaller surface area of grass.
increases with crop density.
soil water: subsurface water in the soil and subsurface layers above
water table. water may be:
- absorbed
- held
- transmitted downwards → water table
- transmitted upwards → soil surface and atmosphere.
coarse-textured soils: much of water is held and fairly large pores at low
suctions.
- field capacity: the amount of water held in the soil before
saturation.
- wilting point: range of moisture content in which permanent wilting
of plants occurs.
Seasonal variations in soil moisture budgets:
- soil moisture deficit: degree to which soil moisture falls below field
capacity. Soil moisture deficit is very low during late winter and
early spring in temperate areas due to high levels of precipitation.
- soil moisture recharge: occurs when precipitation exceeds
potential EVT - some refilling of water in the dried-up pores of the
soil.
hydrological cycle: interaction between atmosphere, lithosphere and
biosphere
drainage basin system: open system which allows movement of
energy and mass through its borders
Outputs
evaporation: liquid into gas, most important in oceans.
- increases in warm, dry conditions and decreases in cold, calm
conditions.
- losses are greater in arid and semi-arid climates than in polar
regions.
- factors affecting rate:
● meteorological factors: temperature, humidity and wind
speed.
● water availability
● vegetation cover
● colour of surface
evapotranspiration: process by which water escapes from a living plant
(stomata or surface of leaf) and enters the atmosphere.
- represents most important aspect of water loss
- pure evaporative losses occur over ice, snow fields, rock slopes,
desert areas, water surfaces and bare soil.
- factors affecting rate:
● factors affecting evaporation
● plant adaptations: cacti reduce water loss.
potential evapotranspiration: difference lies in concept of moisture
availability; water loss that would occur if there was an unlimited supply
of water in soil for the use of vegetation.
river discharge: movement of water in channels.
- may enter river directly as precipitation or by surface runoff,
groundwater flow or throughflow.
, Stores
interception: water that is caught and stored by vegetation. increases
rate of infiltration. Three main components:
- vegetation storage: water retained by plant surfaces , later
evaporated away or absorbed by a plant - varies with plant type
- throughfall: water that either falls through gaps in vegetation or
drops from leaves
- stemflow: water that trickles along twigs and branches, and finally
down the trunk
less from grasses than from woodland - smaller surface area of grass.
increases with crop density.
soil water: subsurface water in the soil and subsurface layers above
water table. water may be:
- absorbed
- held
- transmitted downwards → water table
- transmitted upwards → soil surface and atmosphere.
coarse-textured soils: much of water is held and fairly large pores at low
suctions.
- field capacity: the amount of water held in the soil before
saturation.
- wilting point: range of moisture content in which permanent wilting
of plants occurs.
Seasonal variations in soil moisture budgets:
- soil moisture deficit: degree to which soil moisture falls below field
capacity. Soil moisture deficit is very low during late winter and
early spring in temperate areas due to high levels of precipitation.
- soil moisture recharge: occurs when precipitation exceeds
potential EVT - some refilling of water in the dried-up pores of the
soil.
