Hello, Englishnerd and Ahmed—I agree with you, Ahmed, that "falls" is the best choice of the four. ("Fills" doesn't work at all; "pours" and "drops" are rather silly.) Most English speakers would phrase the sentence differently, so that "rain" is a verb, not a noun, and weather "it" is subject. Another option is to use "rain" as a noun but have expletive "there" as the grammatical subject.
- In Egypt, it rains mostly near the northern coast.
- In Egypt, there is rain mostly near the northern coast.