Water Cycle | Hydrological Cycle | Environmental Science | EVS | LetsTute

In our previous session we learnt about the
availability of water in various forms also we saw the various uses
of water. moving ahead, in this session we shall see Where does the
water in the atmosphere come from? How is water available for our
various uses in a continuous manner? Lets go step by step. STEP 1-EVAPORATION Friends, do you know how the wet clothes which
we hang on the rope dry up? Where does all water from the clothes
vanish? Water does not actually disappear but because
of the suns heat, it changes from one form to another i.e water
which is in the liquid state changes to gaseous state. In the very similar manner water continuously
disperse during the day from the various waterbodies like rivers,
streams, ocean, lakes etc to form water vapour. And so the process where
water changes from its liquid state to gaseous state is called as
EVAPORATION. Every second 16 million tones of water eva[poartes
from the surface of the earth. But Evaporation is not limited to these waterbodies
itself.Even the plants and animals contribute to some amount
of water vapour in the air. You might be wondering how? Plants and animals when they respire release
some amount of vapour in the air like If we keep a glass pane and exhale
air on it..you will find the surface moisture laden this is because of
respiration. When plant release water in the form of vapours through small
openings in the leaves we call this process TRANSPIRATION. The two process in combination called EVAPO-TRANSPIRATION
contributes to the total amount of moisture in the air. Now lets move to the next step..what happens
to the water vapor in the STEP 2-CONDENSATION These vapors are so light that it travels
high up in the air and combine with dust and smoke to form cloud droplets
or crystals of water(also called snow crystals). the droplets or crystals
combine with each other and increase in size. So we can say clouds
are nothing but visible mass of liquid droplets. The process of CLOUD FORMATION
takes place high up in the sky as the temperature there is much cooler
as compared to the one near the ground. cloud can have droplets as
well crystals but it depends on temperature. But these drlets are soo tiny
and light that it cannot fall so they remain as a cloud. Here the water in the vapour form is converted
to liquid droplets so we call this process as CONDENSATION. The same process can be observed when we boil
water with closed lid. The steam or vapour condenses to give us water
droplets on the lid. Whether we see it or not, This cloud formation
occurs continuously untill it reaches a point where it cannot hold any
more water droplets. In other words we can say it has reached its saturation.
Here the tiny light droplets starts combining with each other
to form large droplets. The larger droplets are so heavy that it starts
falling. STEP 3- PRECIPITATION And this atmospheric water then reaches the
land either in the form of rain or snow. we call this process as PRECIPITATION
which is a latin word meaning to fall from. How big do you feel are these raindrops? They
are smaller than a centimeter. It ranges from 0.25 cm to 0.6
cm. Some findings says that many planets of our
solar system receive rainfall but this is different from that of our planet
earth. Like rain on venusb is made of sulphuric acid and due to the intense
heat it vaporizes before it reaches the surface. On reaching the land surface the water is
distributed in different parts: The water either flows off directly into rivers,
oceans, lake which are the surface water body and this process is
called SURFACE RUN OFF. Some amount of water seeps down or diffuses
into the ground by gravity to give us ground water. Friends have you
seen how the water immediately seeps down when we water the plants in a pot.
So ground water formation happens in a similar way and this is called
PERCOLATION. Or infilteration Friends did you observe something. The water
has actually returned to where it was earlier present. thus completing
a cycle. This process of evaporation condensation and precipitation
which maintains a continuous circulation of water in the nature is called
water cycle or hydrological cycle. So the various water bodies are continuously
replenished through water cycle. But which of these water bodies you
think would serve as sources of water for our day to day use? To find the answer to this question tune into
our coming session. I hope you liked this session. Till we meet the next
time keep watchin keep learning .thank you

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