Flood, downpour (6)
I believe the answer is:
deluge
This clue is a double definition.
'flood' is the first definition.
(I know that deluge is a more specific form of flood)
'downpour' is the second definition.
(I know that downpour can be written as deluge)
(Other definitions for deluge that I've seen before include "Overwhelm with water" , "Severe flood" , "A heavy downpour of rain" , "Inundation" , "Cloudburst, downpour" .)