The heat of sun is used to change water into vapour.The Heat exerted by the sun is affects the evaporation by
   if heat is high then then evaporation rate is high. Naturally in summer the evaporation rate is high and in winter thye evaporation rate is less.
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Is the is the heat of the son which is the main cause of evaporation. As the intensity of heat increases, the rate of evaporation too increases. Thus, heat of sun and evaporation are directly related/proportional.
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