Water Cycle

The water cycle includes the process of evaporation, condensation and precipitation. The heat of the Sun evaporates the water resulting in the formation of water vapour. When water vapour cools down, it condenses and forms clouds.

What is Water Cycle?

It is from clouds that the water precipitates in the form of rainfall, hail and snow. This process through which water keeps on changing its form and circulates between the oceans, atmosphere and land is known as the water cycle.


Phenomena Associated with the Water Cycle


Evaporation:

The process in which water gets heated and enters the atmosphere in the form of water vapour is known as evaporation. Heating of oceans, seas, lakes and rivers causes evaporation. Factors which lead to higher rate of evaporation:

  • Humidity: Evaporation is maximum when the air is dry and less humid.
  • Supply of Heat: High temperature or heat results in an increased pace of evaporation.
  • Winds: Strong and dry winds cause quick evaporation of water. This is the reason that clothes dry quickly when the winds are strong.

Latent Heat:

Hidden heat changes solid into liquid or water vapour or liquid into vapour without any change in the temperature.

Condensation:

It is a process by which the water vapour gets converted to tiny droplets of water or ice. Condensation occurs only when water vapour is added to saturated air or when the temperature falls below the temperature at which the air saturates. Following conditions should exist for condensation to take place:

  • Large amount of water vapour should be present in the atmosphere.
  • Small particles of dust, salt and smoke should be present as water vapour condenses around these particles.
  • The air temperature should be below the dew point.

Humidity:

  • The process of evaporation adds water to the atmosphere. This changes the water from the liquid form to the gaseous form. Water vapour which is present in the atmosphere is known as humidity.
  • Absolute humidity is the content of water vapour present in the given volume of air. It is expressed in terms of grams per cubic metre (grams of water vapour present per cubic metre of air).
  • Relative humidity is the ratio between the actual amount of water vapour present in the air and the maximum amount of water the air can hold at that temperature. It is expressed in percentage.
  • It can be measured by applying the following formula:
  • Relative Humidity = the actual amount of water vapour present in the air/the maximum amount of water vapour the air can hold at that temperature × 100
  • Dew point is the temperature at which air gets fully saturated.
  • Specific humidity is the actual amount of water vapour present in a given mass of air.
  • Humidity is measured by a hygrometer which is also known as the Dry and Wet Bulb Thermometer.

Clouds

  • Clouds are masses of small water droplets or small crystals of ice which float in the atmosphere away from the surface of the Earth.
  • When warm air rises into the sky, it cools down and condenses into small droplets of water around dust particles floating in the air. When billions of droplets of water come together around dust particles, clouds are formed.

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