lec 8: Global Hydrological Cycle Flashcards
a closed system globally
all of earth’s water was originally formed in space , when the earth first formed as a planet water was not available
currently thought that all water on earth originally arrived on comets and other extraterrestrial objects colliding with early earth
all of this water arrived during earth’s formation, little to no water has arrived on earth since then
water cycle on earth is a closed system, withe the planet as the boundary
an open system on earth
althugh the system is closed globally: conssts of multiple series of open reservoirs connected by linkages
reservoirs function on different time scales and can hold different volumes of water
their impact on the environment also varies despite all being dependent on the same molecule
71% of earth’s surface is covered in water, incredibly abundant molecule
vast majority of earths water is held in the ocean reservoir 96.5% of all global water
2% glaciers
1% in all the rest
major reservoirs
atmosphere, terrestrial water, oceans
major linkages
evaporation
(liquid water to water vapour)
transpiration
condensation
(water vapour to liquid vapour)
precipitation
(condensation under gravitational pull)
sublimation
movement of runoff
condensation rate
how much water is moving from a vapour to a liquid state over time
depends on the vapor pressure in the air directly in contact with the liquid water
Vapour pressure = how many water molecules are in a parcel of air at any one moment
condensation occurs when a water molecule in the air comes into contact with a water molecule in the liquid (more vapour water molecule in the air = more chance that collision occurs)
evaporation rate
how much water is moving from a liquid state to a vapour state over time
depends on the temperature of the liquid, the warmer the liquid the faster the rate of evaporation
evaporation occurs when a water molecule in a liquid has enough energy to break free of the chemical bonds within the liquid and enter the atmosphere
need for physical substance to form a basis for condensation
in the atmosphere= dust particle , chemicals produced by plants and more
you can see the physical process of condensation, it forms fog or a cloud
fog is a cloud!
seeding point
once the liquid water drop is large enough to be acted on by gravity = precipitation!
temperature affects the ability of condensation to form in the atmosphere in 2 ways
- changes the size of a parcel of air above a body of water
and the rate of condensation is dependent on vapor pressure - changes in the rate of evaporation
and RH is dependent on the rate of condensation and evaporation
transpiration
conversion of liquid water to water vapor by plants , evaporation through a biological linkage
sublimation
movement of water molecules directly from a solid state to a vapour state, with no intervening liquid state
desublimation/deposition
movement of water molecules directly from a vapour state to a solid state
movement of runoff
all water that falls on land as rainfall must eventually drain into the ocean reservoir
some rainfall spends a period of time in a water reservoir on land, such as ake or groundwater
some rainfall moves relatively quickly back into the ocean
direct runoff, movement through rivers
Summary of the global hydrological cycle
- evaporation results in liquid water being converted to water vapour in the atmosphere
- water vapour condenses to liquid water in the atmosphere
- gravity results in the removal of liquid water from the atmosphere in the form of rain
- 78% of rainfall occurs over the oceans, and ends up right back in the ocean reservoir
- The remainder falls over land
some drains directly back into the oceans
some ends up in longer term reservoirs
eventually even the water stored in these long term terrestrial reservoirs ends up back in the ocean
residence time
also called retention time
the average amount of time water spends within the reservoir
res time = res volume/flow rate
if the system is in a steady state: it can calculate the residence time of a reservoir
