The quantity of water in
the universe is constant in quantity and continuously in motion. The same water
molecules is transferred time and time again from the oceans and the land
surface into the atmosphere by evaporation, dropped on the land as
precipitation, and transferred back to the sea by rivers and groundwater. This
endless circulation is known as the “hydrologic cycle”.
the universe is constant in quantity and continuously in motion. The same water
molecules is transferred time and time again from the oceans and the land
surface into the atmosphere by evaporation, dropped on the land as
precipitation, and transferred back to the sea by rivers and groundwater. This
endless circulation is known as the “hydrologic cycle”.
The illustration above shows
the hydrologic cycle in which water leaves the atmosphere and falls to earth as
precipitation where it enters surface waters or percolates into the water table
and groundwater and eventually is taken back into the atmosphere by
transpiration and evaporation to begin the cycle again.
the hydrologic cycle in which water leaves the atmosphere and falls to earth as
precipitation where it enters surface waters or percolates into the water table
and groundwater and eventually is taken back into the atmosphere by
transpiration and evaporation to begin the cycle again.
The different processes are
explained below:
explained below:
·
Evaporation:
As water is heated by the
sun, surface molecules become sufficiently energized to break free of the
attractive force binding them together, and then evaporate and rise as
invisible vapour in the atmosphere.
Evaporation:
As water is heated by the
sun, surface molecules become sufficiently energized to break free of the
attractive force binding them together, and then evaporate and rise as
invisible vapour in the atmosphere.
·
Transpiration:
Water vapour is also
emitted from plant leaves by a process called transpiration. Every day an
actively growing plant transpires
5 to 10 times as much water as it can hold at once.
Transpiration:
Water vapour is also
emitted from plant leaves by a process called transpiration. Every day an
actively growing plant transpires
5 to 10 times as much water as it can hold at once.
·
Condensation:
As water vapour rises, it
cools and eventually condenses,
usually on tiny particles of dust in the air. When it condenses it becomes a
liquid again or turns directly into a solid (ice, hail or snow). These water
particles then collect and form clouds.
Condensation:
As water vapour rises, it
cools and eventually condenses,
usually on tiny particles of dust in the air. When it condenses it becomes a
liquid again or turns directly into a solid (ice, hail or snow). These water
particles then collect and form clouds.
·
Precipitation:
Precipitation in the form
of rain, snow and hail comes from clouds. Clouds move around the world,
propelled by air currents. For instance, when they rise over mountain ranges,
they cool, becoming so saturated with water that water begins to fall as rain,
snow or hail, depending on the temperature of the surrounding air.
Precipitation:
Precipitation in the form
of rain, snow and hail comes from clouds. Clouds move around the world,
propelled by air currents. For instance, when they rise over mountain ranges,
they cool, becoming so saturated with water that water begins to fall as rain,
snow or hail, depending on the temperature of the surrounding air.
·
Runoff: Excessive rain or snowmelt can produce overland flow
to creeks and ditches. Runoff is visible flow of water in rivers, creeks and
lakes as the water stored in the basin drains out.
Runoff: Excessive rain or snowmelt can produce overland flow
to creeks and ditches. Runoff is visible flow of water in rivers, creeks and
lakes as the water stored in the basin drains out.
·
Percolation:
Some of the precipitation
and snow melt moves downwards,percolates
or infiltrates through cracks,
joints and pores in soil and rocks until it reaches the water table where it
becomes groundwater.
Percolation:
Some of the precipitation
and snow melt moves downwards,percolates
or infiltrates through cracks,
joints and pores in soil and rocks until it reaches the water table where it
becomes groundwater.
·
Groundwater:
Subterranean water is held
in cracks and pore spaces. Depending on the geology, the groundwater can flow
to support streams. It can also be tapped by wells. Some groundwater is very
old and may have been there for thousands of years.
Groundwater:
Subterranean water is held
in cracks and pore spaces. Depending on the geology, the groundwater can flow
to support streams. It can also be tapped by wells. Some groundwater is very
old and may have been there for thousands of years.
