Flooded area used to be source of hope (5)
I believe the answer is:
awash
'flooded' is the definition.
('awash' can be a synonym of 'flooded')
'area used to be source of hope' is the wordplay.
'area' becomes 'a' (maths abbreviation).
'used to be' becomes 'was' (I've seen this before).
'source of' suggests taking the first letters.
The initial letter of 'hope' is 'h'.
'a'+'was'+'h'='AWASH'
(Other definitions for awash that I've seen before include "With the top just covered with water" , "Deluged" , "Doused in water" , "Crawling" , "Partly under water" .)