Climate

Hello, I know that the following sentence is awkward English but I'm not sure how that can be said:
Roberts investigated the matter in the hot climate of California, US.

Although you can say "California has a hot climate", we don't usually use "climate" to describe the weather at a particular time. Since both "hot" and "climate" carry other meanings, "hot climate" here could mean "politically sensitive atmosphere", for instance.

Assuming you do mean hot to refer to temperature, "in the California heat" would be better. I cannot think of a way to incorporate "US" into that phrase, but is it needed?

So if I use weather instead of climate would it be correct?

Badmar said:

So if I use weather instead of climate would it be correct?

Your original sentence1 seems OK to me, but we need some context (background) and the source of the example.

1 apart from "US", which you do not need and should not use - see Uncle Jack's comment.