He's referring to the general outcry that will be raised against him. The people of Salem had already begun to question his motives when he discovers that Abigail has run off with his money (and his reputation). He knows that not only will he lose his job, but also his reputation. Once word of mouth spreads he will not be able to get a job in another town.
Also keep in mind that Parris is a man solely concerned with his reputation. Knowing this, it is easy to see why he would be concerned with the things people will say about him. He knows that they will be vocal and awful in the things they say.
It is important to remember a few details about this quote. One, at what point of the play does he say this ( the context of the quote)? The other, why does playwright Arthur Miller choose the word "howl" to characterize Parris in this line?
The quote is referring to Parris' response to Thomas' comment of the possibility of being accused of having witchcraft in his house. Parris lives in constant fear of his community. He does not trust his parish.
Remember that in plays the characters are developed through the words they speak. They are carefully chosen by the playwright for that reason.
So, let's look at the word howl. The definiton of "howling" is an sound/action of a group of wild dogs often heard at night after a successful hunt. The connotation ( shade of emotional meaning) is more powerful when the word spoken gives the audience perspectives that a character is feeling.
Parris is a fearful character who is constantly sucked in by the antics and hysteria of others. Parris' use of "howl" illustrates his attitude toward the "pack of wild dogs" that is his community. The use of language is Miller's way of illustrating Parris as a character and reveals how Parris feels about the other members of his community.
If Parris would have said "they will run me out of town" it would not have the same imagery. "Howl" is a derogatory ( put down) in reference to members of his community. Parris obviously does not respect the people he serves: he thinks of them as wild dogs that will hunt him down if given a reason.