In my field study Environment Eng. disaster is used for natural happenings which cause irreparable results in the nature and human beings' lives, but I have seen and read people use them for different or similar matters. Could you please make clear what the correct usage of those terms is?
This website describes the difference between a disaster and a catastrophe as follows:
In my own understanding of the words, I would describe a catastrophe to be a disaster of such high magnitude that you could not have prepared for it, because you would not have expected that something so bad could happen.
EDIT: @J.R. reminded me about the less literal usage of the two words, which you could use to say that things turned out badly, for example:
In this hyperbolic form, I believe that disaster is more common, but you could use catastrophe if you really want to exaggerate.
When Disraeli, then out of power, was asked the exact same question, he explained:
(Here is a reference)