This isn't a standard way to capitalize, and there's no simple way to describe it.
We can say that "drip" is in lowercase, "Drip" is capitalized, and "DRIP" is in all-caps. There is no simple term for the others.
Here is how I personally would describe it, although it's not a perfectly precise description:
"The writer suggests that the drip is getting louder by repeating the word 'drip' five times, first in lower case, then capitalizing one more letter each time, so that the fifth repetition is in all-caps."