Population increase, decrease etc do not matter. The definition of genocide:
Genocide is an internationally recognized crime where acts are committed with the intent to destroy, in whole or in part, a national, ethnic, racial, or religious group. These acts fall into five categories:
- Killing members of the group
- Causing serious bodily or mental harm to members of the group
- Deliberately inflicting on the group conditions of life calculated to bring about its physical destruction in whole or in part
- Imposing measures intended to prevent births within the group
- Forcibly transferring children of the group to another group
Per the definition of genocide, you only need to commit 1 of the 5 crimes, with the intent to destroy, in whole or in part a national, ethnic, racial or religious group.
Israel has time and again, both shown intent (their own politicians have) and committed atleast 3 of the 5 crimes above.