After outlying event, this essentially sees arid remnant transformed (13)
I believe the answer is:
mediterranean
'after outlying event this' is the definition.
The definition suggests a singular noun which matches the answer.
'essentially sees arid remnant transformed' is the wordplay.
'essentially' indicates the central letters.
'transformed' indicates anagramming the letters.
The central letters of 'sees' are 'ee'.
'ee'+'arid'+'remnant'='eearidremnant'
'eearidremnant' is an anagram of 'MEDITERRANEAN'.
Can you help me to learn more?
(Other definitions for mediterranean that I've seen before include "Sea linking three continents" , "Sea south of Europe" , "Inland sea" , "Sea north of Africa" .)