calamity最重
adversity和misfortune程度一样,可互换
mishap最弱
字典为证(柯林斯字典):
Acalamityisaneventthatcausesagreatdealofdamage,destruction,orpersonaldistress.(FORMAL)
Adversityisaverydifficultorunfavorablesituation.
=misfortune
Amishapisanunfortunatebutnotveryseriouseventthathappenstosomeone.