The water cycle has no starting point. But, let’s begin with large bodies of water. The sun, which drives the water cycle, heats water.Some of it evaporates as vapor into the air. Evaporation rates increase as the temperature increases. (In fact, we sweat because the process of evaporation removes heat from the environment.Water evaporating from your skin cools you.)Rising air currents take the vapor up into the atmosphere, along with water evaporated from the soil and water transpired from plants. The combination of these two processes is what we call evapotranspiration. The vapor rises into the air where cooler temperatures cause it to condense into clouds. Air currents move clouds around the globe; cloud particles collide, grow, and fall out of the sky as precipitation. Some precipitation falls as rain. Some falls as snow and can accumulate as ice caps and glaciers, which can store frozen water for thousands of years. Snow packs in warmer climates often thaw and melt when spring arrives, and the melted water flows overland as snowmelt. Most precipitation falls into bodies of water or onto land where, due to gravity, the precipitation flows over the ground.Some soaks back into the soil and is used by plants to survive and grow.Some, especially water on bare ground, continues to flow as surface runoff. A portion of runoff enters rivers in valleys, with stream flow moving water toward larger bodies of water (even oceans). Runoff and groundwater seepage accumulate and are stored as freshwater in lakes. Not all runoff flows into lakes though. Much of it soaks into the ground. Some water infiltrates(seeps) deep into the ground and replenishes aquifers (porous subsurface rock that holds water), which store huge amounts of freshwater for long periods of time. Some infiltration stays close to the land surface and can seep back into bodies of surface water (and the ocean) as groundwater discharge, and some groundwater finds openings in Earth’s surface and emergesas freshwater springs.
It may sound as if all of the water is always moving. In fact, much more water is “in storage” for long periods of time than is actually moving through the water cycle.
There are four main stages in the water cycle. They are evaporation, condensation, precipitation and collection. Let's look at each of these stages.
Evaporation: This is when warmth from the sun causes water from oceans, lakes, streams, ice and soils to rise into the air and turn into water vapour (gas). Water vapour droplets join together to make clouds!
Condensation: This is when water vapour in the air cools down and turns back into liquid water.
Precipitation: This is when water (in the form of rain, snow, hail or sleet) falls from clouds in the sky.
Collection: This is when water that falls from the clouds as rain, snow, hail or sleet, collects in the oceans, rivers, lakes, streams. Most will infiltrate (soak into) the ground and will collect as underground water.
The water cycle is powered by the sun's energy and by gravity. The sun kickstarts the whole cycle by heating all the Earth's water and making it evaporate. Gravity makes the moisture fall back to Earth.
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