Concerning or involving calamity, disastrous. (adjective)
Examples of word calamitous
By this it appears that it was advisable and seasonable only in calamitous times, and times of present distress, 1
To give to them who are thus marked an assurance of God's favour, that they may know it themselves; and the comfort of knowing it will be the most powerful support and cordial in calamitous times.
Such an attack would truly be "calamitous" -- to use the same description as the Chairman of the U.S. Joint Chiefs of Staff, Admiral Michael Mullen.
We will recall the calamitous response to that disaster, during which some kids weren't reunited with their families for up to six months.
I'm not sure I would want to turn Goodwin's sympathies on, say, Woodrow Wilson, lest personal feeling claim a larger portion of her focus than the long-term calamitous consequences of a president's good intentions; but cynicism doesn't get anyone very far with Lincoln.
Rather than be an alarmist and claim that Global Warming caused it, lets turn what the Al Gores of the world would call a calamitous event into a situation that actually creates jobs and economic prosperity.
That is what is most calamitous, that is the most dramatic.