Water is nature’s basic element. Nearly 70% of earth’s surface is covered by water (Huntington, 2006). Water provides life to all animals and plants. To have water levels on earth remain constant; the process of the water cycle, which is the movement of water on and below, and above earth’s surface, has to occur. Processes such as evaporation, condensation, sublimation and infiltration among others at all help in maintaining the water level on the planet at a constant level to support life on the planet.
Evaporation and condensation are the first and second steps respectively (Huntington, 2006). Evaporation is a process which entails water on the earth’s surface evaporating. As water absorbs energy from the sun, it changes into vapor. The primary sources of evaporation are water bodies such as seas, oceans, lakes, and rivers. Through this process, water finds its way into the atmosphere from the hydrosphere. Also, through evaporation, the temperature of these water bodies falls. The second step is condensation (Huntington, 2006). Through evaporation, water rises into the atmosphere. At very high altitudes, water changes its state from gaseous form to solid as ice. The vapor can also change into water droplets. When these tiny particles come together, they form clouds in the sky or fog.
Sublimation is the third step of the process. Another process which brings about water vapor in the air, apart from evaporation is sublimation. Sublimation is the process where ice turns into vapor without first changing into the water in liquid state (Huntington, 2006). Low temperatures and high pressure accelerate the process of sublimation. The North and South Poles ice sheets are the primary sources of water from sublimation. Mountain ice caps also contribute to water vapor from sublimation. Precipitation then occurs after sublimation. Due to wind and temperature change, clouds in the sky pour down in the form of rain or snow. Precipitation happens when the tiny water vapor droplets in the sky combine to form bigger masses. Another condition that may bring about precipitation is when water concentration in the air is too high, and air cannot hold anymore. Water droplets lose their heat energy at high altitudes due to the low temperature in these regions. In high altitudes where the temperature is less than zero degrees, water pours down as snow. Water may also precipitate through other forms such as hail, drizzle or sleet. Through this process, water gets into the lithosphere.
After precipitation, transpiration is the next step. After precipitation, some water gets into the soil. Pants then absorb this water through their roots; hence water getting into the transpiration process. Transpiration is the process through which plants lose water into the atmosphere through their stomata (Schlesinger et al., 2014). Because photosynthesis is an essential process for plants, they absorb water to use when making their food. However, plants often absorb more water than needed. The plant, therefore, loses the excess water into the atmosphere as vapor through the stomata (Schlesinger et al., 2014). Through this process, water finds its way into the biosphere and leaves into the gaseous phase.
Water runoff and infiltration are the second last and last steps respectively. When water pours from the sky, it leads to a runoff. Runoff is a process where water which has fallen in the form of rain, snow, sleet or drizzle runs over the earth’s surface. Through the runoff, water displaces some soil and mineral elements and carries with them into streams, rivers, lakes, oceans, and seas. After this step, infiltration occurs. Infiltration is the last step of the water cycle. Not all the water that falls from the sky ends up in water bodies, is absorbed by plants or evaporates. Some water percolates into the deep soils and rock. This process raises the level of the water table. The water on the water table is often clean and drinkable. One can measure infiltration as inches of water the soil absorbs per hour.
- Huntington, T. G. (2006). Evidence for intensification of the global water cycle: review and synthesis. Journal of Hydrology, 319(1), 83-95. Accessed from the Web at https://people.ucsc.edu/
- Schlesinger, W. H., & Jasechko, S. (2014). Transpiration in the global water cycle. Agricultural and Forest Meteorology, 189, 115-117. Accessed from the Web at http://www.as.wvu.edu