Page 48 - 新思维科学学生用书7 样章

2.4 The water cycle

Water falls on the Earth

The precipitation that falls then
collects in rivers and open water
such as large lakes and the oceans.

How it is collected depends on
where it lands. Some precipitation

will fall directly onto the rivers, lakes
and oceans and will evaporate, then
the cycle starts again.

If the precipitation falls on plants it
may evaporate from the leaves back to

the atmosphere or trickle down to the
ground. The plant roots in the ground
may then take up some of this water.

Water in the ground

Some of the water from precipitation will soak into the soil and rocks as
groundwater. Some of this water will stay in the shallow soil layer and will

move towards streams and rivers. When groundwater soaks deeper into the
soil, it refills underground stores.

In cold climates the precipitation may build up on land as snow, ice or glaciers.
If the temperatures rise, this solid snow and ice will melt into liquid water,
which soaks into the ground or flows into rivers or the oceans.

Some of the precipitation will soak into the soil and move through
the ground until it reaches the rivers or the open water, large lakes

and the oceans.

Water that reaches the surface of the land may flow directly across the ground
into the rivers, lakes and oceans. This water is called surface run-off. When
there is a lot of surface run-off, soil can be carried off the land and into the
rivers. This can cause them to become silted up and blocked.

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