Hydrologic cycle is a cycle in which water is
continually moving within and above the earth. There are
six major components of this cycle: evapotranspiration,
condensation, precipitation, infiltration, percolation
and runoff. Concepts and components of the hydrologic
cycle are as follows:
EVAPOTRANSPIRATION
Evapotranspiration is the combined result of two
processes: evaporation and transpiration.
Evapotranspiration uses a larger portion of
precipitation than the other processes linked with the
hydrologic cycle.
Evaporation is the process of returning damp to the
atmosphere. Water on any surface, especially the
surfaces of mud holes, ponds, streams, rivers, lakes,
and oceans, is warmed by the sun's heat until it reaches
the point at which water turns into the vapor, or
gaseous, form. The water vapor then rises into the
atmosphere.
Transpiration is the process by which plants go back
moisture to the air. Plants take up water through their
roots and then lose some of the water through pores in
their leaves. As hot air passes over the surface of the
leaves, the moisture absorbs the heat and evaporates
into the air.
CONDENSATION
The cooling of water steam until it becomes a liquid. As
the
dew point is reached,
water vapor forms tiny visible water droplets. When
these droplets form in the sky and other atmospheric
conditions are present, clouds will form. As the
droplets collide, they merge and form larger droplets
and eventually,
precipitation will
occur.
PRECIPITATION
It is moisture that falls from the atmosphere as rain,
snow, sleet, or hail. Precipitation varies in amount,
intensity, and form by season and geographic location.
These factors force whether water will flow into streams
or penetrate into the ground. In most parts of the
world, records are kept of snow and rainfall. This
allows scientists to decide average rainfalls for a
location as well as categorize rainstorms based on
duration, intensity and average return period. This
information is crucial for crop management as well as
the engineering design of water control structures and
flood control.
INFILTRATION
Infiltration is the entry of water into the earth
surface. Infiltration constitutes the only source of
water to maintain the growth of plants and it helps to
sustain the ground water supply to wells, springs and
streams. The rate of infiltration is influenced by the
physical character of the soil, soil cover (i.e.
plants), water content of the soil, soil temperature
and rainfall intensity. The terms infiltration and
percolation are often
used interchangeably.
PERCOLATION
The descending movement of water through soil and rock
is called Percolation. Percolation occurs under the
root zone. Ground water percolates through the soil
much as water fills a sponge, and moves from space to
space along fractures in rock, through sand and
gravel, or through channels in formations such as
cavernous limestone. The terms
infiltration and percolation are often used
interchangeably.
RUNOFF
The movement of water, frequently from precipitation,
across the earth's surface towards river channels,
lakes, oceans, or depressions or low points in the
earth's surface is Runoff. The individuality that
affects the rate of runoff includes precipitation
period and intensity as well as the ground's slope,
soil type and ground cover.
Human Impact on water
Cycle
The earth's water supply is constant, but man is able
to changing the series of this fundamental supply.
Population increases, rising living standards and
industrial and economic growth have placed greater
stress on the natural environment. Man activities can
cause inequity in the hydrologic equation and can
affect the quantity and quality of natural water
resources available to current and future generations.
Water used by households, industries, and farms have
increased. People demand clean water at reasonable
costs, yet the amount of fresh water is limited and
the easily accessible sources have been developed. As
the population increases, so will our need to withdraw
more water from rivers, lakes and aquifers,
threatening local resources and future water supplies.
A larger population will not only use more water but
will discharge more wastewater. Domestic,
agricultural, and industrial wastes, including the
intensive use of pesticides, herbicides and
fertilizers, after overload water supplies with
hazardous chemicals and bacteria. Also, poor
irrigation practices raise soil salinity and
evaporation rates. These factors contribute to a
reduction in the availability of potable water,
putting even greater pressure on existing water
resources.
Large cities and urban sprawl particularly affect
local climate and hydrology. Urbanization is
accompanied by accelerated drainage of water through
road drains and city sewer systems, which even
increases the magnitude of urban flood events. This
alters the rates of infiltration, evaporation, and
transpiration that would otherwise occur in a natural
setting. The replenishing of ground water aquifers
does not occur or occurs at a slower rate.
Together, these various effects determine the amount
of water in the system and can result in extremely
negative consequences for river watersheds, lake
levels, aquifers, and the environment as a whole.
Therefore, it is vital to learn about and protect our
water resources.
