Try our second KS3 Geography quiz on the water cycle. The water cycle is powered by the Sun. The Sun's heat causes water to evaporate from seas, rivers, lakes and the soil. The water vapour goes into the air. Plants also put water vapour into the air by the process of transpiration. Warm air can hold more moisture than cold air so if warm air cools down, clouds will form as the water vapour condenses to form tiny droplets. The more moisture there is in the air, the thicker the clouds. If there is a lot of moisture in the air, the small droplets will merge together and fall as precipitation. The type of precipitation depends on the temperature of the air in the cloud.
About seventy percent of the Earth's surface is covered by water. It is therefore not surprising to find that about eighty percent of the total annual precipitation falls on the seas and oceans. The water cycle is an important part of climate and weather and is also involved in reshaping the geological and other physical features of the Earth, through the processes of erosion and sedimentation.