Answer:
that depends on the calamity. Some calamities however, can't be prevented, like many natural disasters. An earthquake for instance, is caused by suck great forces of nature, that we can't prevent it from happening. What we can do, is create a plan to minimise damage. so for instance you'll be able to evaquate many people quickly from the disaster area.
still, your question is quite general. with some calamities you can do more than with others.