The ground's wet for half the winter (7)
I believe the answer is:
terrain
'the ground's' is the definition.
(terrain is land or ground)
'wet for half the winter' is the wordplay.
'wet' becomes 'rain' (wet weather).
'for' is a charade indicator (letters next to each other) (I've seen this in other clues).
'half the' suggests halving the letters.
'winter' cut in half is 'ter'.
'rain' put after 'ter' is 'TERRAIN'.
(Other definitions for terrain that I've seen before include "Tract of land with prevailing characteristic" , "Area of ground with a particular characteristic" , "(Type of) ground" , "Trainer (anag) - land" , "Land of a particular type" .)