The Hydrologic Cycle
The hydrologic cycle is the process, powered by the sun’s energy, which moves water between the oceans, the sky, and the land. We can start our examination of the hydrologic cycle with the oceans, which hold over 97% of the planet’s water. The sun causes evaporation of water on the surface of the ocean. The water vapor rises and condenses into tiny droplets which cling to dust particles. These droplets form clouds. Water vapor usually remains in the atmosphere for a short time, from a few hours to a few days until it turns into precipitation and falls to the earth as rain, snow, sleet, or hail. Some precipitation falls onto the land and is absorbed (infiltration) or becomes surface runoff which gradually flows into gullies, streams, lakes, or rivers. Water in streams and rivers flows to the ocean, seeps into the ground, or evaporates back into the atmosphere. Water in the soil can be absorbed by plants and is then transferred to the atmosphere by a process known as transpiration.
