Water moves in a continuous movement from the oceans to the air, then it moves from the air to the upper layers of the atmosphere to return to the earth and from there to the water sources again in a natural cycle that occurs regularly on the earth, which is the water cycle in nature, and the water cycle in nature ensures the continuous movement of water between the earth The atmosphere, also known as the hydrological cycle, consists of successive phases, namely, evaporation, condensation, precipitation, and flow, and the water distribution varies between these stages, but the total amount during the water cycle remains constant.
Evaporation is one of the basic stages in the water cycle, and what happens during the process of evaporation is the transfer of water molecules from the surface of the water to the atmosphere, since when water molecules have kinetic energy that allows them to separate from each other, their liquid state changes to rise in the atmosphere in the form of water vapor in Its gaseous state, and this energy comes from the sun’s heat and is responsible for breaking down water molecules and separating them from each other.
Among the most important factors affecting water evaporation are temperature and humidity, in addition to the wind speed, and one of the most important sources of water vapor in the atmosphere is the oceans, and ice and snow play a major role in increasing the proportion of water vapor in the atmosphere when it is transformed from a solid-state to a gaseous state from During the sublimation process without passing through the liquid state, as evaporation occurs in the soil as well, and evaporation occurs in vegetation through the process of transpiration, and water vapor is one of the main factors leading to the formation of moisture in the atmosphere and the formation of fog, clouds, and precipitation. It can be said that the oceans, seas, and lakes contribute approximately 90% of the atmospheric moisture through evaporation, while plants contribute about 10% of the atmospheric moisture through the process of transpiration, and evaporation stops when the atmosphere reaches the degree of saturation, i.e. the humidity in it reaches 100%. And water vapor remains in the atmosphere in a region called the troposphere, which is the region below the altitude of 10-13 km, equivalent to 6-8 miles.
Condensation is a process in which water vapor turns from a gaseous state to a liquid state, and it is the primary means by which water returns to the earth, so what happens during condensation is the exact opposite of what happens in evaporation, and condensation occurs when the atmosphere is filled with water vapor particles, that is, it reaches a state Saturation, and when the air masses whose temperature is different mix with each other, when the water vapor rises in the air it cools, and the sun, in turn, heats the air near the surface of the earth and when the air temperature rises, its weight becomes light and rises to the top to meet the cold air, and then condensation occurs and clouds form And clouds.
After clouds form, rain falls, and if the water vapor cools to a suitable degree for the snow to form, then it falls the snow, and the steam falls in the form of rain, as the water vapor condenses at the beginning on the particles of dust or smoke suspended in the atmosphere to be the core on which the raindrop is formed Then these raindrops collect to form clouds, but they do not fall directly due to the rising air, which in turn raises them upward, which prevents them from falling, but when the clouds are filled with water droplets and become heavy, the water particles collide with each other, and when the collision increases and is very fast they fall Rain, or when a small drop of water joins with a drop of larger than it, then the drop of water that results from them has a very heavyweight that the cloud cannot carry, so it falls in the form of rain.
After falling on the surface of the earth, the rain is distributed in four main ways, some of which evaporate and return to the atmosphere again, and some of it is absorbed by the vegetation and expelled into the atmosphere through the process of transpiration again, and there is part of the rainwater that is absorbed by the soil to enter it and permeate its layers, where water forms The groundwater is part of it, and there is the remaining part going on the surface of the earth to pour into the seas and oceans, and studies have shown that about 75% of the rainwater falls over the seas and oceans, while the water that penetrates the soil and becomes part of the groundwater can flow slowly in the rocks until it returns to rivers, to pour into the sea at the end, and from the groundwater that is formed what remains inside the earth and seeps deep into the aquifer.