The Water Cycle
Think About It:
 Why is there humidity?
 There is moisture in the air.
 Why is there moisture in the air?
 It evaporates from lakes and oceans.
 Solar radiation causes it to change its state.
Remember:
 Water takes longer to warm and cool because of its
high heat capacity.
 Lots of solar energy is needed to change the state
of water!
 Solid
 Ice


Liquid
Water


Gas
Vapour
Changing States of Water
 Melting – solid to liquid
 Evaporating – liquid to gas
 Endothermic – absorption of heat.
 A lot of energy is needed for these changes.
 This is why it takes a long time for the temperature
in the spring to rise significantly even when the days
are longer and there is more sunlight. Most of the
Sun’s energy is used to melt the snow and ice.
Changing States of Water
 Condensing – gas to liquid
 Solidifying (freezing) – liquid to solid
 Exothermic – the release of heat.
 A lot of energy is released during these changes.
 This is why the temperature falls slowly in autumn
even though there is significantly less sunlight. The
freezing water is releasing heat.
The Water Cycle
 The hydrologic cycle.
 Water continually cycles through the biosphere.
 It circulates, continuously, through the oceans,
atmosphere, and land in different forms.
This About It:
 Describe the processes of the water cycle.
 Water vapour condenses to form clouds, which result
in precipitation when the conditions are suitable.
 Precipiation falls to the surface and infiltrates the
soil or flows to the ocean as runoff.
 Surface water evaporates, returning moisture to the
atmosphere, while plants return water to the
atmosphere by transpiration.
The Water Cycle
Condensation:
 Water vapour in the air rises because of convection.
 As it rises, the water vapour loses energy.
 This causes its temperature to drop, causing it to
change from gas to liquid (water droplets) or solid
(ice or snow).
The Water Cycle
Precipitation:
 The water droplets or ice pellets are too heavy to
remain in the atmosphere.
 They fall.
The Water Cycle
Infiltration:
 Some precipitation reaches land and seeps into the
ground.
 This is now groundwater.
The Water Cycle
Runoff:
 Precipitation that does not infiltrate will drain into
creeks, streams, and rivers, which eventually add
to the water levels of lakes and oceans.
 Some runoff will evaporate or infiltrate during its
travels.
The Water Cycle
Evaporation:
 Solar radiation heats the water on Earth.
 This causes it to gain energy.
 This causes it to rise into the atmosphere as vapour.
The Water Cycle
Transpiration:
 Plants take in water through their roots and release
it through their leaves.
 It is released into the atmosphere.
The Water Cycle
 Heat Transfers in the Water Cycle:
 page 21
EXOTHERMIC
ENDOTHERMIC