Notes-Class 7- Science-Chapter-10-Disaster Management-Maharashtra Board

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There are two types of disasters, viz, man-made and natural disasters. They are linked together. Some disasters can be prevented while during some disasters, we can take precautions.

• Due to phenomena of climate change, the frequency of natural disasters is increased.
• Natural disasters such as famine, lightning strikes, cloudbursts, storms, etc. result due to climate change.
• During such calamities, there is possibility of loss of life and damage to property.

Famine:
(1) Long term and severe scarcity of food grains and water, results into famine.

(2) Famine is categorized as mild famine and severe famine,

(3) Mostly famine is due to natural causes but sometimes because of human activities a famine like condition can arise.

(4) Asia is the most famine affected continent of the world.

Causes of famine :

• Drought is the most important cause for famine,
• Heavy rains and floods due to which crops getting washed away or damaged.
• Environmental changes such as climate change and global warming.
• Damage of crops due to attack of pests, locusts or diseases. Damage caused by animals like mice and rats.
• A natural calamity like earthquake, storms, cold or fog.
• Man-made causes of famine are war, internal unrest, absence of transport routes, uncontrolled population growth, etc.

Man-made causes of famine:

(1) Imbalance between rainfall and increased human population

(2) The excessive demand for water resulting into water scarcity. Unlimited lifting of water and its misuse.

Due to green revolution there is increase in the production of food grains. But at the same time there is environmental imbalance due to excessive use of chemical fertilizers, pesticides and weedicides, it causes erosion of land.

Ways to ease the severity of a famine.

(1) Planning for usage of water along with its reuse.

(2) Adopting practices of water conservation and harvesting at the local level.

(3) Large scale plantation of trees and prevention of deforestation.

(4) By taking into account the weather forecasts the appropriate changes in agricultural practices, should be adopted.

Cloudburst:

(1) Cloudburst means very heavy rains as if a cloud has burst. It occurs when there is sudden raining over a specific and small region at a rate of 100 mm per hour or more.

(2) Water coming down from rain clouds does not reach the land in the form of rain. But due to very high temperature near the land, it vapourizes again and goes back into the same clouds. This results in very high amount of water vapour in clouds which result into cloudburst.

(3) Incidences of cloudburst: In Leh (Ladakh) on 6th August 2010 and in Mumbai on 26th August 2005, On July, 20, 2017, a cloudburst at Thathri town of Doda district caused huge damage and killing more than 7-8 people. In Belagavi, Karnataka on May 4, 2018, a cloudburst had occurred. Weather stations in the area reported 95mm rain in an hour.

Floods :

During floods, water is accumulated at one place in a very large amount. This is caused due to heavy rainfall. The river may also overflow and spread its water along the banks.

Effects of flood :

(1) Huge loss to life and property. The excessive rain water cannot be drained due to choking of drain pipes.

(2) Transportation and electric supply gets halted.

(3) Soil erosion takes place resulting into damage to farms and crops. Cattle lose their life.

(4) The epidemics spread and harm the health of the people after the flood water recede.

Protective measures in view of floods :

(1) Constructing small dams and percolation tanks in mountainous regions.

(2) Making river beds flat. Connecting rivers.

(3) Mass tree plantation and thereby cultivation of new forests

Government interventions :

• Government of India has established the National Flood Commission in 1976.
• The Commission tries to control floods.

 Lightning:

(1) Temperature of lightning is more intense than that of the sun

(2) About 95% of the lightning flashes occur only in the sky whereas only 5% of lightning reaches the ground.

(3) Generation of lightning occurs either within one cloud or between two clouds. Sometimes it takes place between a cloud and the ground.

(4) In the atmosphere, about forty lightning flashes occur per second

(5) There is very high temperature, due to lightening. This causes sudden expansion of the air under high pressure which results into loud thundering.

(6) Generally lightning strikes maximally on the open ground. The chances of lightning falling on the open ground are higher than that of under the tree or near water. At high places or near tall object, the chances of lightning strike are much higher. Lightening can kill a person or there are long term harmful effects. Immediate treatment of lightning affected persons is essential to save their life.

(7) Proper precautions should to be taken during thunder storms:

Volcano :
A volcanic eruption is a natural phenomenon in which the solid, liquid and gaseous substances below the earth's crust which are very hot are pushed towards the crust. When they come out of the crust, it results into an eruption causing great damage.

Effects of a volcano :

• The molten lava, vapour, hot mud, sulphur, etc. are collected on the surface of the earth forming mountains and hill.
• The air pollution occurs due to ash and gases ejected by the volcano. It often rains due to effect of volcanic eruption.
• The hot gases that are emitted out, raise the temperature. Settlements and forests may get buried under the hat mud.
• Volcanoes erupt in the sea too, causing formation of an island. This may form upheaval of water and creation of huge waves.
• It is impossible to prevent the eruption of a volcano and to control the effects of eruption. However, now due to progress in science and technology, the earthquake activity can be predicted. Some immediate steps for disaster management are taken if it is needed.

Tsunami :

(1) Tsunami means 'harbour wave'. It is a huge wave, formed due to an earthquake or volcano occurring on the ocean floor. The energy released pushes the sea water upwards. Due to this tsunami waves are formed which are not very high near the source. These waves spread very fast to long distances with the velocity of 800 to 900 kilometer/hour

(2) Upon reaching a coastal area, their velocity is reduced, but their height increases tremendously, to about 30 meters. At the coastal region they cause tremendous destruction.

Destructive effects of tsunami. 

• Large scale damage to life and property. Great financial loss.
• Infrastructures like buildings, bridges etc. collapse.
• The industries related to the sea are adversely affected. Large scale damage is caused to harbours, boats and ships.
• Trees are uprooted and landslides take place on a large scale.
• Original land forms change near the coast giving rise to swamps.
• Transportation is affected due to damaged roads.
• Normal day-to-day life is disrupted.

Precautionary measures for 'Tsunami:

With the help of an artificial geostationary satellite prediction about Tsunami can be understood. It gives an immediate estimate about the progress of tsunami. In such prediction, people from coastal area are warned and relocated to save their lives.
Storms:

There is formation of high and low air pressure belts in the atmosphere. This causes strong winds to blow. The weather suddenly changes due to this resulting into storms.

Effects of storm : There is a large scale damage to the property and life. The storm affected regions are greatly damaged. The electric supply and transportation is disrupted.

Precautionary measures against storms:

(a) If you are away from home : take shelter at the safe place.

(b) If you are in your home: stay safe with all possible precautions.
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