The water cycle is important because it results in the distribution of water on land surface, purifies water, supports plant growth, facilitates agriculture and sustains aquatic ecosystem. The water cycle promotes human civilization and development.
The water cycle, also known as the hydrological cycle, is the circulation of water as ice, liquid and vapor throughout the earth and its atmosphere. The cycle begins with the evaporation of water from large water bodies and transpiration from plant leaves. This vapor rises up to the upper atmosphere and condenses due to low temperatures. Condensed water vapor accumulates resulting in the formation of clouds. Due to the effect of winds, the clouds are often blown away to other areas. Accumulation of clouds and subsequent saturation leads to the formation of water droplets which fall back to the earth as rainfall. In some instances, the water droplets are exposed to very low temperatures hence the formation of sleet, hail or snow. The water from precipitation finds its way into rivers and streams which channel them back to the large oceans and lakes. Hence the cycle repeats itself.
The following are some of the important contributions of the hydrological cycle.
Distribution of Water The hydrological cycle facilitates the distribution of water on the earth‰Ûªs surface. The cycle takes the sea water and irrigates the land surface through rainfall. In addition, the presence of streams and rivers on the earth‰Ûªs surface assist in the distribution of water. In this regard, without the hydrological cycle, water would be constrained in seas and oceans, resulting in dry and arid land.
Purification of Water Oceans, seas and some lakes contain salty water which is unsuitable for human consumption. Evaporation of such water helps in the purification process since the salts and other impurities are left behind.
Moreover, the infiltration of surface water into the ground assists in the purification process. Infiltration leaves behind solid particles and impurities thus ensuring only clean water finds its way into porous rocks. This water may later emerge on the surface of the earth as springs, providing clean water for human consumption.
Supports Plant Growth The water cycle results in the formation of rainfall and other forms of precipitation. Water from precipitation supports plant growth. In addition, the seasonal flooding of rivers in lowlands leads to the deposition of fertile soils on the flood plains. Such fertile soils promote agricultural activities and growth of vegetation.
Supports Aquatic Ecosystem Aquatic plants and animals largely depend on the presence of fresh clean water for survival. Animals such as fishes, crocodiles, frogs and snakes, and plants such as marshes, grasses and water lotuses constitute the aquatic ecosystem. These plants and animals would be unable to survive in inland environments without the presence of rivers, streams and lakes. In this regard, the hydrological cycle ensures that inland water bodies have water hence the sustenance of aquatic ecosystems.
Growth of Human Civilization and Development The growth of human civilization greatly depends on the availability of clean water for domestic and industrial use. Free flowing water in rivers may be used for water transport, irrigation, as raw material for industrial processes or for generation of hydro-electric power. In this regard, the water cycle is essential for human civilization and development.