The use of would and is in the paragraph

Solution 1:

The verb in you would pass is not in the past tense, but is a conditional open to the possibility of taking the described journey sometime in the future, at least as an imaginative exercise.

If you were to take a journey from north to south, you would see...

In this context, the choice of a conditional, the present, or future in the first clause is purely stylistic.

On a journey from north to south across this huge region, you pass through a fascinating series of hot tropic landscapes and plenty of rain falls in the far south, whereas the arid northerly region is prone to serious drought.

On a journey from north to south across this huge region, you will pass through a fascinating series of hot tropic landscapes and plenty of rain falls in the far south, whereas the arid northerly region is prone to serious drought.

The present tense invites the reader to imagine the journey as generic truth; the future to anticipate the dramatic change in landscape. The grammatical differences are slightly different ways of engaging the reader’s imagination.

That the north is arid and drought-prone is in the present tense because it is a statement of fact. Houston often floods. Philadelphia is miserable in August. New York City is full of yellow taxis.

Solution 2:

The author has used "would" to create an effect on the reader that if he/she does travel through this region, he would experience "fascinating series of hot tropic landscapes" and "plenty of rain falls in the far south". The author has used present tense to indicate that the "arid northerly region" is currently prone to serious drought. It wouldn't make sense for the author to say - "whereas the arid northerly region was/will be prone to serious drought." - because the area is still prone to serious drought emphasizing that the arid northerly region is not so fascinating. Therefore, the author is stating a fact. The author presents us with two possible situations, i.e., if you go here you would (generally) experience this, but if you go there you would (generally) experience something else.

Using "will" in this context is like telling a person (who does not know about the place) what he will experience if he/she decides to go to either place.

Hope this helps!