Supplement: The sentence is a response. There's a context before the sentence. And the "where ..." part is a clause. So, the sentence is not saying "get sunburnt because of staying in the tropics" but responding "That's because the city is in the tropics. And in the tropics, many people get sunburnt."

The city is in the tropics where the horrible/blazing sunshine can burn people’s skin. … Because isn’t necessary here.

We would not normally begin a sentence with 'Because', but if this was a response to a question by characters in a book then it reads perfectly well. I think the apostrophe is in the correct place. I hope that helps.

It has a grammar mistake. You begin with the word "because," which is part of the pattern "Because X, Y follows," there isn't any Y. The word "where" introduces a clause that explains the word "tropics." I can't explain what's wrong but "where the horrible sunshine there" isn't right, either. Also, the apostrophe ought to go after the letter "s" in "peoples'" Here are several correct sentences: "Because the city is in the tropics, where the horrible sunshine can burn peoples' skin, everyone uses sunscreen." BECAUSE the city is in the-tropics-where-the-horrible-sunshine-can-burn-people's-skin [THEREFORE] everyone uses sunscreen. "Because the city is in the tropics, the horrible sunshine can burn peoples' skin." BECAUSE the city is in the tropics [THEREFORE] the horrible sunshine can burn peoples' skin. We can put in an optional "there." It doesn't change the meaning, but it emphasizes that the reason has to do with location: "Because the city is in the tropics, the horrible sunshine there can burn peoples' skin." P.S. Just as a matter of factual detail, you don't need to be in the tropics to get sunburn!

‘Horrible’ and ‘sunshine’ don’t go together. ‘Sunshine’ is positive and ‘horrible’ wouldn’t normally apply to either Sun or sunshine. The city is in the tropics and the intense sun there burns the skin. (If the speaker is human we know he is talking about human skin) The tropical Sun (of this city) can cause sunburn. It’s also factually a strange thing to say because sunburn can occur outside of the tropics. What you probably mean is that people are more susceptible to sunburn there compared to somewhere else.