The water cycle is the continuous journey water takes from the sea to the sky, to the land and back to the sea. The water cycle describes the existence and movement of water on, in and above the Earth. Earth’s water is always in movement and is always changing states, from liquid to vapor to ice and back again. The water cycle is also known as the hydrologic cycle. The movement of water around our planet is vital to life as it supports plants and animals. Powered by the Sun, the water cycle is happening all the time.
Stage 1
The water on land turns into vapor in the atmosphere and this occurs in three main ways – (1)evaporation, (2)sublimation and (3)transpiration.
- Evaporation - This is the main process by which water goes from the ground and change to vapor in the atmosphere. Around 90 percent of the water vapor in the atmosphere comes through evaporation. The sun’s rays heat up the water on the surface of the earth’s oceans and cause it to change into water vapor and rise into the air, this is called evaporation. Evaporation is more intense in the presence of warmer temperatures. Strongest evaporation occurs over the oceans and near the equator.
- Sublimation – This is when water moves directly to vapor from ice or snow without ever melting into water. Good conditions for sublimation to occur is when ice or snow is in very cold conditions, but it is windy and the sun is shining.
- Transpiration – Transpiration is the process by which plants return moisture to the air. Plants take up water through their roots and then lose some of the water through pores in their leaves. These small pores are called 'stomata' which are found on the underside of leaves. As the hot air passes over the surface of the leaves, the moisture absorbs the heat and evaporates into the air. Plants will release a lot of water as they grow.
Stage 2
Once high up in the sky, the water vapor begins to cool and turns back into a liquid; this is called (4)condensation.
Stage 3
The water droplets form clouds which become heavy and fall from the sky in the form of rain, sleet, hail or snow, this is called (5)precipitation. Most precipitation falls as rain.
After precipitation occurs three things can happen to precipitation.
- The first thing that can happen is that the water will soak into the ground and could stay there forever – (6)Infiltration
- The second thing that can happen is that it will fall directly into rivers and lakes and oceans and other bodies of water – (7)Accumulation
- The third thing that might happen is that the precipitation will land on mountains and will run down them into rivers and lakes and oceans and other bodies of water – (8)Runoff
Oceans and lakes collect water that has fallen. This water again evaporates into the sky again and the cycle continues.
