The most common and most likely answer to this crossword clue is the 4 letter word AREG
A
R
E
G
More clues leading to the result AREG
Buddy explains!

The straight part
We know that "Dry zone" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case dry zone = areg.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does AREG mean?
AREG noun- A large desert region of sand dunes with little or no vegetation, especially in the Sahara.