A natural disaster is unforeseen, severe and immediate. Pollution, ozone depletion in the stratosphere and global warming come in this category. Natural disasters include cyclones, earthquakes, floods, drought (though these two are now being increasingly considered ‘man- made’ disasters) heat and cold waves, landslides, avalanches, flash floods, severe thunderstorms, hail, low level wind shears, and microburst.
The destructive potential of any natural hazard is estimated basically by its spatial extent and severity. Spatial extent upto which the effect of a disastrous event could be felt may easily be classified into small, medium and large scales. The phenomenon extending from a few kilometers to a few tens of kilometers are termed as small scale.Growing industrialisation and unjustified exploitation of natural resources have brought our echo system to a verge of non-reversibility and imbalance. This has led to a threat from a set of natural hazards like pollution, global warming and ozone depletion on large or global scale.