This question already has an answer here:
I was listening to Hikawa Kiyoshi's ソーラン節 and instead of 浴びる he said 浴びりゃ， is there a normal pattern for this kind of pronunciation? Is it regional?
This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.
Song lyrics tend to take poetic license, but if not, this is a shortening of 「浴びれば」. As far as I'm aware, it's not regional, since I hear it in common speech in Tokyo and on television programs.