Question

explain in detail why evaporation is called surface phenomenon.

Answer 1

Evaporation is called a surface phenomenon because we put water in the presence of sunlight with duration in time the temperature starts increasing and the hydrogen bonds of H20 from surface starts breaking and dissociated molecules move upward and therefore evaporation takes place from the surface but not inside. 

Answer 2

if we keep water in the presence of sunlight after sometime we observe that the temperature has increased
the hydrogen bonds of water from surface starts breaking and it gets dissociated 
the dissociated molecules move upward
and evaporation takes place in the surface 
inside the layer the water does not get evaporated but only the surface of water gets evaporated 

therefore evaporation is called surface phenomenon.