Dry deserted country briefly in the ascendant (4)
I believe the answer is:
arid
'dry' is the definition.
('arid' can be similar in meaning to 'dry')
'deserted country briefly in the ascendant' is the wordplay.
'deserted' becomes 'd'.
'country' becomes 'iran' (I've seen this before).
'briefly' means to remove the last letter.
'in the ascendant' says the letters should be written backwards.
'd'+'iran'='diran'
'diran' with its last letter removed is 'dira'.
'dira' backwards is 'ARID'.
(Other definitions for arid that I've seen before include "Very dry, having little rain" , "Without water" , "Dry and parched, as with regions" , "water shortage?" , "Dry and infertile" .)