这四个词都有灾难的意思。
disaster为普通用词，用于描述所有类型的灾难。
例子：Thousands died in the disaster.
calamity侧重灾难带来的悲伤。
例子：It will be a calamity for farmers if it keeps raining.
catastrophe侧重灾难的结局。
例子：Food is required immediately to avert a humanitarian catastrophe.
cataclysm意为大动荡，宽泛的来说可以表示所有剧变。
例子：an international economic cataclysm