The number increases in emergencies (6)
I believe the answer is:
crises
'emergencies' is the definition.
(I've seen this in another clue)
'the number increases' is the wordplay.
'the number' becomes 'c' (C is an example).
'increases' becomes 'rises' (rise is a kind of increase).
'c'+'rises'='CRISES'
'in' acts as a link.
(Other definitions for crises that I've seen before include "lot of emergencies" , "difficult moments" , "Moments of panic" , "Catastrophes" , "desperate situations" .)