The water cycle.

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Water covers 70% of the earth's surface and is vital to all living things. Water is always circulating between the earth's surface and the atmosphere in the water cycle.

Many processes work together to keep the Earth's water moving in a cycle. There are five processes at work in the hydrologic cycle:

  1. Condensation

Condensation is the process of water changing from a vapour to a liquid. Water vapour in the air rises mostly by convection. This means that warm, humid air will rise, while cooler air will flow downward. As the warmer air rises, the water vapour will lose energy, causing its temperature to drop. The water vapour then has a change of state into liquid or ice.

  1. Precipitation

Precipitation is water being released from clouds as rain, sleet, snow, or hail. Precipitation begins after water vapour, which has condensed in the atmosphere, becomes too heavy to remain in atmospheric air currents and falls.

  1. Infiltration

A portion of the precipitation that reaches the Earth's surface seeps into the ground through the process called infiltration.

The amount of water that infiltrates the soil varies with the degree of land slope, the amount and type of vegetation, soil type and rock type, and whether the soil is already saturated by water. The more openings in the surface (cracks, pores, joints), the more infiltration occurs. Water that doesn't infiltrate the soil flows on the surface as runoff.

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  1. Runoff

Precipitation that reaches the surface of the Earth but does not infiltrate the soil is called runoff. Runoff can also come from melted snow and ice.

When there is a lot of precipitation, soils become saturated with water. Additional rainfall can no longer enter it. Runoff will eventually drain into creeks, streams, and rivers, adding a large amount of water to the flow. Surface water always travels towards the lowest point possible, usually the oceans. Along the way some water evaporates, percolates into the ground, or is used for agricultural, residential, or industrial purposes.

  1. And evapotranspiration.

Evapotranspiration ...

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