Water in liquid state changes to vapour in gaseous state by heat .The heat of the earth causes water to change  to water vapour. It is not always necessary to heat the water to change it to water vapour. The sun heats rivers, oceans, seas, etc. and causes water to evaporate and that forms clouds.

Evaporation is faster when:  

1. Temperature is high.

2. Exposed surface area is more.

3. Weather is dry.

4. Weather is windy.

Following are the experiments to prove the above points.

Expt1: We take two wet handkerchiefs of same size and cloth . One we keep in the sun and other inside the room. The one kept in the sun dries first because the temperature is high under the sun.

Expt.2 Again we take two handkerchiefs of same size and cloth .One I keep it open  and other one I fold it twice. We keep them for drying. Which one is going to dry faster ? The answer is the one which one is not folded because it has more exposed surface area and more the exposed surface area more is the evaporation.

Expt3: Cloths take less time to get dry in the dry weather because  the dry weather does not have much water vapour present in it .Thus it can readily accept water  vapour formed by evaporation.

Expt4: Take two saucers. Add equal quantity of water in both of them . Keep one saucer under the fan and the other without the fan. The water in the saucer under the fan is going to evaporate faster. This shows us that evaporation is faster when it is windy.