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Water Cycle

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  • July 2008
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WATER CYCLE

Water Cycle, also known as hydrologic cycle, is a process that is constantly recycling the Earth's supply of water. This is important because humans, animals, and plants all need water to survive. It is controlled by the sun, which produces energy in the form of heat. This heat energy causes the water in the world's oceans, lakes, etc. to warm and evaporate. As the water is heated, it changes its phase from liquid to gas. This gas is called water vapor and this process is called evaporation. When plants give off water vapor, it’s called transpiration. When water evaporates, it rises into the cooler air, collects, and forms clouds. There, the water vapor molecules cool down and change back into liquid water. This is called condensation. As more and more water vapor cools into the clouds, the water droplets that form the clouds become larger and larger. When the swirling winds in the atmosphere can no longer hold them up, the droplets fall from the sky and precipitation is the term for the falling, condensed water molecules, which come down as rain, snow, sleet, or hail depending on conditions in the atmosphere. When water falls to the Earth, the water seeps into the soil because of the force of gravity. This seeping is called infiltration. Or the water flows over the land and into bodies of water, such as rivers and lakes.

Evaporation (the importance)

The water cycle is powered from solar energy. 86% of the global evaporation occurs from the oceans, reducing their temperature by evaporative cooling. Without the cooling effect of evaporation the greenhouse effect would lead to a much higher surface temperature of 67 °C, and a warmer planet. Most of the solar energy warms tropical seas. After evaporating, water vapor rises into the atmosphere and is carried by winds away from the tropics. Most of this vapor condenses as rain in the Intertropical convergence zone, also known as the ITCZ, releasing latent heat that warms the air. This in...