Evaporation is the process of which water changes from its liquid state to gaseous form.
This process takes place at all places, at all times and at all temperatures except at dew point or when the air is saturated.
The rate of evaporation is affected by several factors. Important among them are as under:
Accessibility of water bodies —
The rate of evaporation is higher over the oceans than on the continents.
Hot air holds more moisture than cold air.
The rate of evaporation is more in summers than in winters.
That is why wet clothes dry faster in summers than in winters.
If the relative humidity of a sample of air is high, it is capable of holding less moisture.
On the other hand if the relative humidity is less, it can take more moisture.
Hence, the rate of evaporation will be high.
Aridity or dryness of the air also increases the rate of evaporation.
Wind also affects the rate of evaporation.
If there is no wind, the air which overlies a water surface will get saturated through evaporation.
This evaporation will cease once saturation point is reached.
However, if there is wind, it will blow that saturated or nearly saturated air away from the evaporating surface and replace it with air of lower humidity.
This allows evaporation to continue as long as the wind keep blowing saturated air away and bring drier air.
The cloud cover prevents solar radiation and thus influences the air temperatures at a place.
This way, it indirectly controls the process of evaporation.
About 600 calories of heat is used for converting each gram of water into water vapour.
A calorie is unit of heat energy spent in raising temperature of one gram of water by 100C.
The heat energy used for changing the state of water or a body from liquid to gaseous state or from solid (ice) to liquid (water) state without changing its temperature is called latent heat.