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Short video of rainfall. Red areas indicate heavier precipitation. Visualization courtesy of the NASA Scientific Visualization Studio.

Water is essential for life. About sixty percent of the human body consists of water and it needs to be replenished constantly. 

Water operates in a cyle - evaporating, condensing, precipitating and flowing back to the ocean to continue the cycle. Precipitation is responsible for the deposit of fresh water on Earth. While we would like a steady amount of rainfall to maintain reservoirs, nourish crops, and provide for home consumption and recreation, precipitation patterns vary. Some areas get more than enough precipitation in a year. Lloro, Columbia gets an average of 523.6 inches of rain per year. In North America, the Henderson Lake in British Columbia gets 256 inches per year according to NOAAWeather Underground reports that New Mexico experienced the some of the worst rainfall events during 2013. On the other hand, Arica, Chile gets an average of just 0.03 inches a year! 

Despite local and regional variations, evaporation and precipitation over the whole Earth balance each other. Over continents, precipitation exceeds evaporation, while over the ocean, evaporation exceeds precipitation. Most of the precipitation that falls on land comes from the ocean. About 80 percent of all evaporation comes from the ocean. Winds move the water vapor around the globe, yet 77 percent of all precipitation falls back into the sea. The amount of water in the atmosphere is only a small fraction of Earth's total water supply.

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