Answer: to show that producing drinking water is just one good result of fog collection.
Explanation:
The author use the phrase "a harvest of many benefits" to show that producing drinking water is just one good result of fog collection.
The intent of the phrase was to show how important fog collection was. Apart form the fact that it produces drinking water, it can also irrigate crops and change high deserts into green landscapes.
A semicolon can be used to combine two closely related independent clauses if they are not already joined by a coordinating conjunction (and, but, or, nor, for, so, or yet).
