The water cycle

In a nutshell

The different stages of the water cycle include: evaporation, condensation and precipitation. These processes are important for the Earth's weather system.

Water cycle

Definition

The water cycle is the constant cycle of the movement of water on Earth, changing between a liquid and a gas.

Science; States of matter; KS2 Year 4; The water cycle

1.	Evaporation
2.	Precipitation
3.	Condensation
4.	Water drains back into oceans and lakes

Evaporation

Evaporation is when liquid water is heated and changes state to a water vapour gas. The sun will heat water sources on the surface of the Earth, like oceans and lakes. The water will evaporate and turn to a gas known as water vapour that will rise to the sky.

Condensation

The water vapour rises and begins to cool down, condensing to change state to a liquid. This is in the form of clouds filled with water droplets.

Precipitation

When the droplets in the clouds become too heavy they will precipitate and fall as either rain, snow or hail. The water from the clouds will fall back into the oceans and lakes. The cycle will restart and evaporation will occur again.

What does evaporation of water depend on?

Temperature

How quickly evaporation occurs will depend on the temperature. Evaporation of water will happen faster at warmer temperatures, so on a hot day more evaporation will occur compared to a cooler one.

Example

A water puddle will evaporate quicker on a warm day compared to a colder day.

Using weather forecasts

Weather forecasts can be used to predict when evaporation levels will be the highest.

Example

The weather forecast predicts the following for the beginning of the week:

Monday - Hot and sunny.
Tuesday - Cloudy with rain.
Wednesday - No rain, but cool temperatures.

Which day of the week should the washing be hung out?

The evaporation of the water on the clothes will happen faster at warmer temperatures so Monday would be a good day to hang out the washing. The rain on Tuesday will make the clothes wetter so this isn't a good day! The washing could be hung out on Wednesday because there is no rain forecast. However, the rate of evaporation would be higher on Monday as the temperature is higher. So, Monday would be the best day to hang out the washing.