The water cycle in nature
The water cycle in nature or the hydrological cycle is defined as the cycle that is responsible for the movement of water in the Earth's atmospheric system, and it is represented in many processes; Such as evaporation, transpiration, condensation, precipitation, runoff, and others, where water is recycled through this cycle to maintain the existence of water bodies, the continuity of clouds condensation, and precipitation over time.
Phases of the water cycle in nature
The water cycle in nature goes through several stages, namely:
Evaporation is defined as the process by which water changes from a liquid state to a gaseous state, and is the main pathway for the transition of water from its liquid state to the water cycle again in the form of atmospheric vapor.
Thermal energy is one of the main factors in the evaporation process; This is because it breaks the bonds that exist between water molecules, so it evaporates faster when it reaches a boiling point equivalent to about 100 degrees Celsius, It is worth noting that both snow and ice can turn into water vapor through a process called sublimation. ).
The evaporation stage in the water cycle occurs when the surface temperature of the Earth increases due to the sun's rays, as the sun's heat increases the speed of water molecules, increases their kinetic energy enough to be released into the atmosphere in the form of gas.
These particles remain in the atmosphere for about 10 days, during which they rise vertically until their temperature begins to decrease, and when it becomes cold enough, they begin to condense and turn into a liquid state in the form of water droplets suspended in the atmosphere, and then turn into clouds to start the precipitation process.
The evaporation process results in the formation of fresh water; Since the main source of evaporated water in the atmosphere is the salty ocean waters that cover the surface of the earth by 70%, and when the ocean water evaporates, the salt remains and the pure water vapor condenses in the form of clouds and then falls to feed rivers, lakes, and streams with fresh water,
Also, about 90% of the atmospheric moisture comes from the evaporation of the waters of the oceans, seas, and rivers on the surface of the earth, while the rest of the moisture in the atmosphere comes from the process of transpiration of plants.
Plants absorb water through their roots from the surface layer of the soil and release it again in the form of steam through their leaves through a process known as transpiration. the water in it.
Transpiration rates depend on temperature, humidity, availability, and intensity of sunlight, precipitation, soil type and saturation, wind intensity, land slope, and others.
Forests release large amounts of water into the atmosphere through the leaves of their trees and the roots of vascular plants through the process of transpiration; The leaves of plants are the main source of evapotranspiration from forests, which increases the rate of forest drying.*.
The term evaporative transpiration refers to the total evaporation processes emanating from the transpiration of plants on the land and the surfaces of the seas and oceans into the atmosphere. It is one of the most important stages in the water cycle in nature, in which forests play an important role, and water moves from plants to the atmosphere in other ways. The most important of which is the so-called parachute interception *.
Condensation is defined as the process of converting water vapor into liquid water, meaning it is the opposite of the evaporation process.
Clouds are formed when the temperature of vapor decreases due to its rise in the atmosphere, where the temperature at the top is directly related to the decrease in pressure; The total heat content in any system depends mainly on the amount of substance in it.
The higher the altitude above sea level, the lower the air pressure as a result of the decrease in air molecules per unit volume, so the density and temperature of the air decrease.
Water vapor molecules begin to condense around small particles suspended in the air, forming clouds, and it is worth noting that water vapor is an essential component of air, regardless of its quantity, which may vary from time to time.
Humans can see water vapor in the form of fog when it is near the surface of the earth during very humid weather.
Precipitation is defined as the water that falls from the clouds in the form of rain most of the time, or in the form of sleet, sleet, snow, or hail at other times, and this stage is responsible for the transfer of water from the atmosphere to the Earth.
Rain is formed in two ways; The first is when the size of some droplets increases as a result of additional vapor condensation due to the collision of water molecules with each other, and if the collisions are sufficient to produce a drop of water with a falling speed greater than the speed of the rising current of the clouds, This causes the cloud to fall as rain.
The second and most effective way for a drop of water to reach the size of a drop of precipitation is through the Bergeron process, which expresses the growth of ice crystals much faster than the condensation of water vapor in the cloud. The crystals fall as snow or melt and fall as rain.
The following are the most common types of precipitation:
- the rain
Liquid drops of water form when steam condenses around dust particles inside the clouds, forming small drops that continue to inflate until they become too large for the cloud to be able to carry. lower.
- the snow
Small blocks of a frozen waterfall from the sky and each of these blocks are formed from ice crystals when water vapor rises, or when the vapor changes directly from a gaseous state to a solid in the form of snow.
- the cold
Ice grains form in thunderstorms, where the rising air prevents the frozen water beads from falling, and accordingly, the size of the grains begins to increase due to their collision with very cold water drops until the cloud becomes unable to carry hail due to the increase in its mass, which may reach more than 0.68 kg per grain It usually falls in the form of circular grains, and scientists indicate that the speed of hail may reach 128.75 km/h.
- snow rain
A mixture of rain and snow falling from the sky, formed as a result of the freezing of raindrops as they fall to the ground, and the size of its grains is smaller than the size of hailstones and wetter than it.
Runoff occurs when rainfall increases and the soil is saturated; So the surface of the earth becomes incapable of absorbing more water, so rivers and lakes are formed, and then the water returns again to the oceans.
Surface runoff can sometimes cause water to evaporate directly into the atmosphere; When the flowing water flows towards a lake with no outlets for the water to flow out of it, the water will evaporate because there is no other way for the water to return to the atmosphere, and thus the impurities and salts in the lake will increase until it becomes salty; Like the Great Salt Lake in Utah, and the Dead Sea in Palestine.
The importance of the water cycle in nature
The importance of the water cycle in nature lies in the following:
- Providing fresh water necessary for all living creatures on the planet, and renewing its sources on the globe, that is, renewing the water of rivers, seas, and streams.
- Climate regulation.
- Maintain air humidity.
- Provide suitable soil for cultivation.
The effect of the water cycle on the movement of the elements
The importance of the water cycle appears in the effect of the phases of its movement in nature and the patterns of precipitation in it, mainly on the natural systems of the planet.
Runoff and precipitation are also among the most important factors that contribute to the cycle of transmission of various elements; As the element carbon, nitrogen, phosphorous, and sulfur, the runoff process contributes to the transfer of elements on land to different aquatic ecosystems.
The impact of climate change on the water cycle in nature
Climate change affects the percentage of water vapor, cloud formation, types of precipitation, and types of flowing currents that are mainly related to the water cycle in nature, through the following:
- When the air temperature rises, the evaporation of water increases and the air becomes saturated with evaporated water particles, and thus strong rainstorms occur that lead to floods.
- On the other hand, the high temperature of the air and the increased evaporation of water from the ground lead to dryness in the soil, and when rain falls, the soil cannot absorb it, and water flows towards rivers and streams.