CBSE Book Class 8 Disaster Management Cyclones

CYCLONES

12th May 1990

Andhra Pradesh coast was hit by a severe cyclonic storm on 8th May 1990 with wind speed about 240- 250 km/h and 5-6 metre-high storm surges. The area all along the coast of Krishna and Guntur districts was affected severely by the storm, which was accompanied by gales and heavy rainfall. Other areas were affected by flooding due to heavy rainfall. The cyclone affected 9 of the total 23 districts, while the number of villages affected was 5,923. The cyclone killed 928 persons and around 24,000 cattle. A total of about of 7.8 million people were affected by the cyclone. About 827,100 houses were partially damaged while 569,000 were completely destroyed. More than 500,000 hectares of agricultural and horticultural land was affected. Total damage to property was worth Rs 125 million.

Source: Press Release, Government of Andhra Pradesh The extract on the right from a newspaper gives you an idea of the devastating power of a cyclone. The Indian subcontinent is the worst cyclone-affected part of the world, as a result of low-depth of the Ocean bed and the way our coast is shaped. The Indian Ocean is one of the six major cyclone-prone regions of the world.

Look at this picture. It shows children standing outside their school whose roof was partly blown off, during the Orissa Cyclone on 29th October 1999. Every year cyclones take their toll on thousands of people, and property. But the magnitude of destruction can be reduced to a large extent through knowledge and preparedness.

What Is a cylcone?

A cyclone is a region of low atmospheric pressure, which occurs in the hot oceans of temperate and tropical latitudes. It is a swirling atmospheric disturbance, accompanied by powerful winds (exceeding the 300 km/h sometimes) blowing in a clockwise direction in the Northern hemispheres and anti clock wise direction in the Southern hemisphere, by pouring rain, and enormous waves in the ocean. Cyclones occur due to a combination of warm sea temperature, high relative humidity and atmospheric instability.

In a cyclone, clouds gather around a centre that is called the “eye of the cyclone”. A zone of calm, accompanied by good weather characterises the eye. It is in edge of the eye called the “wall of the eye” (in a radius of 20 to 30 kilometres) that the worst conditions prevail, with devastating winds. So, as the eye of the cyclone crosses an area, the wind drops. As it passes, the wind speed rises again, and hence the calm should not be confused as the ‘end’ of the cyclone.

The diameter of the cyclone is often several hundreds of kilometres. That of the eye varies between 20 and 50 km and the cloudy mass of the cyclone raises to occupy all of the troposphere.

What happens during a cyclone?

The principal dangers from a cyclone are:

(i) Gales and strong winds; (that may uproot trees, destroy telephone lines and electricity poles which may disable power and communication)

(ii) Torrential rain that can cause flooding

(iii) High tidal waves (also known as ‘storm surges’). Most casualties are caused by coastal inundation by tidal waves and storm surges.

The rise in water level caused by a storm surge can cause severe flooding in coastal areas, particularly when this surge coincides with the normal high-tide. Preparing for cyclones

Knowing about the areas that are most likely to be hit by cyclones is the first step towards preparedness. Cyclones usually occur between 5-20 degrees latitude, North and South of the equator.

Please refer to the link below for - CBSE Class 8 Disaster Management - Cyclones