Abstraction is the term used to describe the amount of rainfall that doesn’t turn into runoff. There are numerous processes that intercept rainfall. Some rainfall never even reaches the ground, instead being intercepted by leaves on trees, by buildings and some rainfall is evaporated back into the atmosphere, of the rainfall that reaches the ground, some is infiltrated and some just ponds with no outlet.
So processes like evaporation, transpiration, evapotranspiration, interception, percolation, infiltration so on are included in this abstraction of precipitation.
Interception :
When a rain falls it is firstly intercepted by buildings, plants, trees, towers etc., when they become completely wet, then the rain comes down to the earth surface. This initial amount of water used by buildings, plants, trees, towers etc., for getting wet is equal to the evaporation rate. so this complete amount of water is called as interception loss.
Initially while Raining
After Complete Wetting
It is calculated by, x = a + bt
Where,
x = total interception
a = water required for wetting
b = evaporation rate from the intercepting surface
t = duration of rainfall
Interception Loss : water which is retained on surface, and which is later evaporated away is nothing but interception loss.
Interception mainly depends upon the duration of rainfall frequency but very less upon the intensity of rainfall. If the total rainfall is more, the interception may be little more. The interception is expressed as percentage of total rainfall.
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