Energy from the Sun heats the
surface of the Earth.
Water is evaporated from
oceans, rivers, lakes by the sun
The warm, moist air rises
because it is less dense.
Condensation occurs when water vapour is turned back
into water droplets as it cools down and clouds are formed.
Precipitation occurs as water droplets get bigger and
heavier they begin to fall as rain, snow and sleet, etc.
Some water will be intercepted by vegetation
and then will evaporate from leaves
Some of this water will eventually return to the air as
vapour through the process of transpiration. This slows
down or prevents some water flowing back to the river.
Some water flows across the surface of the ground, This is called
surface runoff. This happens when water isn't allowed through
the surface because it is already saturated or impermeable
Some water infiltrates into the soil. This through flow
moves more slowly back to the river than surface run-off.
Some water percolates deeper into the ground and
is slowly transferred back to the river or sea.
Percolation ~ When
water moves
downwards through
the soil.
Stores and Transfers
The major stores of water are the ice caps, land, ocean and the atmosphere.
The movement of water between these stores is called transfers.
River drainage basins
A river basin or drainage basin is an area
of land drained by a river and its
tributaries.
The edge of the drainage
basin is known as the
watershed
This can be compared to a sink or basin, which catches the water falling into
it. The water travels towards the centre and leaves the sink through a plug
hole.
In a similar way, the water flowing through the river will
eventually leave the river basin through its mouth and enter the
sea or a lake.