Actually, birth rate is most closely tied to education.
So by keeping a bunch of men and women essentially trapped in an open air prison for decades with no education, no way to leave, and nothing to do but eat, sleep, and fuck…

Well guess what, they are all going to fuck.

There are other forms of genocide though.
Cultural Genocide is the act of destroying a nation or ethnic groups identity, which fits Gaza pretty well. The IDF are bombing their shit and attacking civilian populations as a means of keeping a cycle of constant cultural struggles so the Palestinians do not have the chance to properly develop and grow, making the chance of a two state solution more plausible. It's no surprise, Israel's hard-right leadership does not want a two-state solution and is wanting to break the Palestinians into complete submission, whether Hamas is there or not.