The Hydrological Cycle

Hydrological cycle describes the continuous water circulation on, above or below the Earth surface which include lithosphere, hydrosphere, atmosphere and biosphere. Without hydrological cycle exist in Earth, biogeochemical cycles could not exist, ecosystems could not function and life could not be maintained (Smith, 1992). Oceans play the main role in the hydrological cycle as they hold 97% of the total water in Earth. Natural processes on Earth rely on the forces produced by the hydrological cycle to support and provide enough water supply for plants, animals and human. Besides, the movements of nutrients, pathogens and sediments also occur in process of hydrological cycle. Solar energy is the driving force behind the cycle. The heating of

Rivers are the primary movers of water over the globe, they tend to balance the evaporation deficit of the oceans. Wetzel (2003) states that precipitated water may either be intercepted or transpired by plants or may run off over the land as surface runoff. However, about 80% of the intercepted water and surface runoff are returned to the atmosphere by evaporation. Besides, precipitated water may also infiltrate the ground. Infiltration is the process of movement of water through the boundary area in the soil. Transfer of water depends on the porosity and permeability of the soil. Infiltrated water may be stored temporarily as soil moisture prior to being evapotranspired. The average renewal time for storage is approximately 280 days (Wetzel, 2003).The storage capacity of the soil is made continually available by evaporation and plant transpiration. When the rate of rainfall or snow melt water influx exceeds the absorptive capacity of the soil, the excess water flows over the surface as overland flow. In general, the intensity of rain increase, the rate of infiltration increases. Some of the water percolate or seep down to an impervious layer of clay or rock to be stored as ground water. In ground water zone, percolation happened which is caused by gravity and capillary forces, the water find its way into streams or springs, and

The evaporation is the process of a liquid converting to the gaseous state. In this cycle, the evaporation occurs when the ocean has been evaporated to the cloud. It occurs from land, the oceans, and other water surfaces. Transpiration is the loss of water by evaporation in ground-dwelling plants, accompanied by a corresponding uptake from the roots. This cycle always supplies forces to help in reducing the water into roots from soil. Precipitation process is a reaction that leads to the formation of a great solid in a light liquid; the precipitate so formed at the bottom of the container. As for runoff is that portion of precipitation on an area which does not penetrate or evaporate, instead, it is being discharged from the area while infiltration is the act of or process of infiltrating, as of water into a porous physical matter. Once the water from precipitation reach the earth, it then becomes runoff and ground water, which balances the water on land before much of it are evaporated back, and the cycles are repeated. Nowadays, human modification of the environment such as clearing of forest or land to build more building, agricultural purposes or any other human development to support the increase in human population have greatly alter the global water balance and the climate. There is a theoretical hypothesis stated that