The most common and most likely answer to this crossword clue is the 8 letter word FLOODING
I've seen this crossword clue in Independent
F
L
O
O
D
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More clues leading to the result FLOODING
Buddy explains!

The straight part
We know that "Disaster" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case disaster = flooding.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does FLOODING mean?
FLOODING verb- To overflow, as by water from excessive rainfall.
- To cover or partly fill as if by a flood.
- To provide (someone or something) with a larger number or quantity of something than can easily be dealt with.
- To paste numerous lines of text to (a chat system) in order to disrupt the conversation.
- To bleed profusely, as after childbirth.
- An act of flooding; a flood or gush.
- Emotional overwhelm sometimes leading to a primal state of rage or panic.