The Water Cycle

Source: Food and Agriculture Organization of the United Nations, 2013, David Coates and Jacquie Grekin, CBD,   "The Youth Guide to Biodiversity" 1st Edition (Chapter 7) Youth and United Nations Global Alliance. Reproduced with permission.

Chapter 7. Verbatim.

The water cycle is the continous movement of water around the planet. During this cycle water can be in various states: solid, liquid or gas. Water moves by processes of evaporation (water turning from a liquid to a gas), transpiration (the movement of water through vegetation and soil), condensation andprecipitation.

Water travels above and infiltrates below the ground and accumulates in rivers, lakes and oceans and evaporates or transpires into the atmosphere where it condenses to form clouds and then returns to the Earth’s surface through precipitation (rain, snow, hail and sleet). 

The changes in the state of water during the cycle requires the exchange of heat, therefore cooling or heating the environment (for example, evaporation requires energy and therefore cools the environment). The water cycle also has the effect of purifying water courses, replenishing water supplies and moving nutrients and other elements to different parts of the world.

Biodiversity (i.e. trees and other plants) is a necessary part of the cycle. The soils in which they are rooted absorb water and store it safely, while their leaf canopies return water, in the form of vapour, to the atmosphere, where it becomes precipitation. Large‑scale removal of vegetation can disturb the cycle, often resulting in changed rainfall patterns and soil erosion. Biodiversity, therefore, supports the availability of water for people and other living things to use.