Geography Reference
In-Depth Information
4
WATER AND ICE
WATER
The water cycle
Water evaporates from oceans, soil, living things (transpiration),
rivers and lakes. At some point this water vapour condenses to
water or ice in the atmosphere and returns to the Earth's surface as
precipitation. Some of this precipitation will infiltrate into the soils
and rocks below the surface where it flows more slowly to river
channels or sometimes directly to the oceans. The water remaining
on the surface and in the upper layers of the soil will partly evapo-
rate back to the atmosphere and partly run into lakes and rivers,
many of which flow into the sea. There are four main stores of
water. These are the world oceans, polar ice, terrestrial waters and
atmospheric water. The oceans hold 93 per cent of the water, polar
ice holds 2 per cent, the soils, lakes, rivers and groundwater hold 5
per cent and the atmosphere holds a thousandth of 1 per cent of
water resources. The water held in glaciers and polar ice or deep
within some rocks may be stored for several thousand years. The
water held by plants may just be stored for a few hours.
Water movement through the landscape
Precipitation can hit the land surface or be intercepted by vegeta-
tion. Some intercepted water can evaporate while some can flow
down plant stems or drip from leaves in order to reach the
land surface. The water that reaches the land surface can either
