All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
There is absolutely no contradiction between what you called as the scientific evidence and the Hadeeth which you mentioned in the question.
The Hadeeth does not mention the number of times that the woman's semen discharge happens and it does not mention how often it occurs whether many or few. Rather, the Hadeeth illustrates a Sharee’ah ruling which is that if the woman sees a semen discharge, she is obliged to perform Ghusl.
Therefore, the Hadeeth does not restrict this to only one time in a month, and it [the Hadeeth] does not imply as well that it may happen more than once in a month, or even in a year, and this is very clear.
Allaah Knows best.