Water cycle called as hydrological cycle, explains how water moves between the surface of earth and through the atmosphere. Water exists in three states – solid, liquid and vapor (gas). The water cycle is all about the processes involved in changing into various states and between major sources like rain, ground and surface (lakes, rivers).
Evaporation happens when water on the surface gets heated up by the sun and changes into vapor state. These vapors rise above and into the atmosphere. Also plants take up water from the soil and release vapor through their leaves or stem. This process is called transpiration. Thus water enters the atmosphere in vapor form due to evaporation and transpiration.
As the hot air rises, it experiences drop in temperature with altitude, cools forming water droplets around tiny bits of dust in the air. This is called condensation. When enough vapors are there, it is nothing but a cloud. As the air gets moister, droplets fall from sky. This is precipitation. It can be in the form of rain, snow, sleet or hail depending on air temperature.
Infiltration is the process of water seeping through the surface into ground. So once in the ground, the water can join the earth's groundwater supply. The water that reaches the surface but doesn’t seep through the ground is called runoff.
Thus water moves in a constant cycle - evaporates from the land, travels through the air, rains down on the land and then flows back to the ocean.
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