The growing food crisis, which is impacted by the Covid pandemic, is turning into a world famine because of the war.

The grave food crisis, which is impacted by the covid pandemic, has led to a world famine caused/ exacerbated by the war. We use "which" here to introduce your relative clause. It gives us more information about the food crisis. It is only extra information (non defining relative clause). Without it the sentence still makes sense. There are other ways to write this. If you need help on using relative clauses for complex sentences please book a lesson. I have quite a few students studying this at the moment.

The grain crisis impacted by the Covid pandemic has brought about a world famine since the war.