PHASES OF THE WATER CYCLE
ATMOSPHERE
BIOSPHERE
OCEANS
TERRESTRIAL
LITHOSPHERE
The water cycle
http://earthobservatory.nasa.gov/Library/Water/water.html
% of all water
Oceans
Freshwater
97.47
2.53
% of freshwater
Ice & snow
69
Groundwater
30
Rivers & lakes
0.03
Atmospheric Water
0.04
IMPORTANCE OF OCEANS
• Oceans as stores or sinks: Water, CO2 , heat,
dissolved salts, sediments.
• Ocean currents as transfer systems.
• Importance of evaporation: source of
atmospheric moisture, latent heat and
energy transfer.
Importance of Ice Caps, glaciers
and snow cover
• Store of water in frozen form (consequences
for sea-level if ice melts)
• Isostatic effects of ice cover and ice melt
• Albedo of ice caps affects global heat
budget
• Extent of glaciation depends on air
temperature and on amount of precipitation
as snow fall – wet periods favour glaciation.
The evaporation process
• Conversion of liquid water to water vapour
• Depends on:
• ENERGY and WATER TEMPERATURE
(related to solar radiation)
• Capacity of air to take up moisture (related
to air temperature, air humidity, wind speed)
Hurricanes
PRECIPITATION
Cloud formation
output of energy
as latent heat
Condensation
Cooling
warming
Input of energy
as latent heat
Uplift of air
Evaporation
Adiabatic processes
Convection
Convergence/frontal systems
Orographic uplift
Distribution of Cloud Cover
source Pidwirny (on line)
January
’84-’91
Red = high cover
Green/yellow =
intermediate cover
Blue = zero cover
July
’83-’90
Distribution of Global Precipitation
source Pidwirny (on line)
Water on the land
evapotranspiration
evaporation
precipitation
soil water
vegetation
natural
ecosystems
agriculture
runoff
water
resources
surface
water
rivers
lakes
groundwater
human livelihoods
domestic
water supply
industry etc.
geomorphological
processes
Vegetation and hydrology
Interception & evaporation of water:
direct loss of water to he
atmosphere
Biomass of
above ground
vegetation
Infiltration: absorption of
precipitation by the soil
Vegetation cover
Surface root mass
Soil organic content
Transpiration: use of soil
moisture by plants
Leaf area, size and structure
Root mass and rooting depth
Significance of hydrological effects of
vegetation
• Evaporation of intercepted water and
transpiration (evapotranspiration) = loss of
water to the atmosphere; reduction in water
available to rivers and groundwater
• Infiltration controls surface runoff process;
low infiltration leads to overland flow and
possible erosion; low soil moisture levels
inhibit vegetation growth.
Vegetation and hydrology 2
EXERCISE: For two selected biomes describe the way in which the
vegetation cover effects hydrological processes.
• WATER AVAILABILITY
– Is this biome found on a wet or dry area?
– Is precipitation seasonal?
– Is rainfall characteristically intense?
•
INTERCEPTION
– Does the above ground biomass act as an effective interceptor of water?
•
INFILTRATION
– Is there a good ground cover that will protect the soil from the impact of raindrops?
Does it vary seasonally?
– Is there a good root matt close to the soil surface?
– Is the underlying soil rich in organic matter?
•
TRANSPIRATION
–
–
–
–
Is there a high leaf biomass?
Is the vegetation evergreen or deciduous?
Are the leaves adapted to prevent excessive water loss?
How deep are the roots?