Rain and other forms of precipitation occur when water accumulates in the clouds and falls to the ground. This occurs due to the water cycle, which continually recycles the water on Earth.
Water on the surface of the Earth can evaporate and rise into the atmosphere. As it rises, the water cools and condenses inside of a cloud. Water is stored in clouds until enough water droplets have accumulated. Then precipitation occurs; depending on the temperature on the ground, the precipitation can be rain, snow, sleet or ice. The cycle constantly repeats itself, but it can be affected by pollution, global warming and climate change.