What is Hydrological cycle?
Hydro-logical cycle, also known as water cycle is the most important of the various cycles of the environment. It involves natural process resulting in the exchange to water between various water bodies, i.e., the oceans, seas, rivers etc. The hydro-logical cycle involves three different and continuous processes, i.e., evaporation of water followed by condensation leading to rainfall. Finally the rain water returns to the water bodies. Water also finds its way into ground water by seepage from the land.
The ground water is again taken up by plants, which in turn release water as vapors in the atmosphere. The hydro-logical cycle can be compared to distillation, which involves vaporization of water by heat.
The vapors on cooling get converted back into liquid form. The water in the oceans moves as it is of different temperature and salinity at different locations. Surface waters are also moved by winds, giving rise to surface ocean currents. Warm water is lighter or less dense than cold water which is more dense or heavier and salty water is also more dense than fresh water. The combination of the water’s temperature and salinity determines whether it rises to the surface, sinks to the bottom, or stays at some intermediate depth.
Water circulates between the living and non-living components of the biosphere in the form of unending cycles. (Fig. Below) Tn hydro-logical cycle, there is movement of water from the oceans to the atmosphere by evaporation and from atmosphere to oceans and land by precipitation, from land to oceans by run off and from streams and rivers and from land to the atmosphere by evaporation. The energy required for the above cycle is provided by the sun in the form of solar energy. Tn the above cycle, water in oceans, seas and lakes, etc. circulates between them and the atmosphere.
n an alternative pathway for hydro-logical cycle, the soil water or the underground water is circulated by plants, animals and the atmosphere. The plants take up the soil water through their root system. A part of this water is utilized by plants for photosynthesis and the excess water is given off into the atmosphere during transpiration. (Transpiration is the loss of water from the leaves of the plants via evaporation).
Transpiration, in fact, is the main source of water into the atmosphere. The decay of dead plants by microorganisms release water back into the soil. Animals consume water by drinking from various sources and also via plants they eat. Water vapor is again released into the atmosphere by breathing and evaporation from the surface of animals (sweating) and excretion.
Whatever the route is followed, the water vapors being lighter rise in the air, where it gets cooled and condenses into tiny droplets to form a cloud. The water from the clouds ultimately falls on the earth in the form of rain, part of which gets absorbed by the soil and the remaining finds its way into water bodies. fig below