Area used to be hot and seriously flooded (5)
I believe the answer is:
awash
'seriously flooded' is the definition.
'area used to be hot' is the wordplay.
'area' becomes 'a' (maths abbreviation).
'used to be' becomes 'was' (ie used to be or was in the past).
'hot' becomes 'h' (abbreviation eg on taps).
'a'+'was'+'h'='AWASH'
'and' is the link.
(Other definitions for awash that I've seen before include "Deluged" , "Letting the 21 in" , "Doused in water" , "Partly under water" , "With the top just covered with water" .)