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Spectroscopy is an important technique used in Chemistry Topics to analyze the interaction of matter with electromagnetic radiation.
Water cycle – Definition, Diagram, Facts and Importance
The continuous circulation of water from the earth’s surface to atmosphere, and from the atmosphere back to earth, is called water cycle in nature. A labelled diagram of the water cycle in nature is given in Figure.
The water cycle in nature can be described as follows. Water is present on the earth in rivers, lakes, ponds, oceans and soil. Some water is also present under the ground.
(i) Heat from the sun evaporates water from rivers, lakes, ponds, oceans and soil to form water vapour. This water vapour goes into the air. The plants and trees absorb water from the soil through their roots. The plants and trees lose water as water vapour by the process of transpiration (through the pores of their leaves). This water vapour also goes into the air.
(ii) The air containing water vapour is heated by the sun. Hot air, being lighter, rises high in the sky. It is cold at high altitudes in the sky. So, when the air containing water vapour rises to a high altitude, the water vapour present in it get cooled. The cold water vapour condense to form tiny droplets of water. These tiny droplets of water form clouds in the sky. The tiny droplets of water in the cloud join together to form bigger drops of water. These drops of water fall down on earth in the form of rain. In very cold regions, the water drops in the sky freeze to form snow (ice). So, water also falls down to earth in the frozen state called snow.
(iii) Water formed by the melting of snow and some of the rain water flows into rivers and finally goes into oceans. The rain water also fills the lakes and ponds, and gets absorbed by the soil. Some of the rain water seeps through the soil and goes under the ground.
In this way, water which was taken from the earth, returns to the earth and hence the water cycle is completed. Once again the water evaporates and water cycle is repeated. The occurrence of water cycle in nature is a continuous process. The water cycle never ends.
Importance of Water Cycle in Nature
Water cycle is important because of the following reasons :
1. Water cycle makes fresh water available in the form of rain. The sea-water is highly salty which is not fit for drinking by animals or for the growth of plants. But the rain water (formed from sea-water by evaporation followed by condensation) is pure water. It can be utilised by animals as well as plants.
2. Water cycle keeps the amount of water on the earth’s surface constant. This is because the water removed from the earth during evaporation and transpiration is put back to the earth during rain and snowfall.
What If It Rains Heavily
Every place in the world gets rains sometime or the other. The time, duration and amount of rainfall varies from place to place. For example, in some parts of the world, it rains throughout the year whereas in other parts it rains only for a few days in a year. In our country, most of the rainfall occurs in the monsoon season (rainy season). Rains are always welcome. Rains give us many advantages. For example :
- Rains bring relief by cooling the environment after hot summer days.
- The sowing of many crops depends on the arrival of rains during monsoon.
- Rains provide water in the rivers and dams of hydroelectric power plants.
- Rains fill the lakes and ponds which act as sources of water.
- Rains are also responsible for the groundwater which gets stored under the surface of earth.
When it rains heavily for a long time, we get excess rainfall resulting in too much water all around. The excessive rainfall due to heavy rains leads to many problems. Some of the problems caused by heavy rains are given below :
(i) Heavy rains in city areas lead to waterlogged roads and streets (see Figure). This disrupts the traffic on roads and causes inconvenience to the people.
(ii) Heavy rains (or excessive rains) may cause floods. This happens as follows : Heavy rains lead to too much rise in the level of water in rivers. The river water starts overflowing from its banks and spreads over a large area of land causing floods (see Figure). The flood water may submerge cities, villages, crop fields, and forests causing damage to property (houses, etc.), human life, domestic animals, standing crops, and wild animals of the forests.
(iii) The animals living in water are carried away by the fast flowing flood waters. These water animals often get trapped on land areas and when the flood water recedes, they die.
(iv) Heavy rains also kill the animals living in soil because such animals do not get air to breathe when all the soil gets covered with flood water.
What Happens If It Does Not Rain For A Long Period
Sometimes it so happens that it does not rain in a region for a year or more. This leads to shortage of water in that region causing dryness everywhere. An environment of dryness is called drought. So, we can say that if it does not rain in a region for a long time it causes drought (or sookha). Drought is a long period without rains leading to severe shortage of water in the region. This happens as follows.
The soil in the fields is normally moist because it has water in it. The soil continues to lose water by evaporation and transpiration. The water lost by soil is usually made up by rains. If, however, it does not rain at all (or the rainfall is very low) for a long period, the loss of water from the soil is not made up and hence the soil becomes dry (see Figure).
Due to lack of rains, the water level in the lakes and ponds also goes down and some of them may even dry up completely. In the absence of rains, no water seeps into the ground and hence the level of groundwater in wells, etc., falls drastically. Due to this the groundwater also becomes scarce. In this way, a prolonged period of no rains (or very low rains) causes all round shortage of water leading to drought. Thus, the lack of rains for long periods may cause drought.
The people living in areas having drought conditions face many difficulties in leading a normal life. Some of the problems faced by the people because of drought in an area are as follows :
- In drought conditions, the soil does not have sufficient moisture (or water) to grow crops well. Since the crop plants do not grow well, drought leads to severe shortage of food for the people in that region.
- In drought conditions, the vegetation such as grass and other fodder does not grow well and leads to shortage of fodder for the domestic animals (like cows and buffaloes).
- Due to shortage of food and fodder, many people living in drought affected areas even migrate to other places along with their domestic animals in search of food and fodder. Some people and do-mestic animals may even die of starvation.