Or HaChaim on Genesis 41:54/אור החיים על בראשית מ״א:נ״ד

1 ותחילנה …כאשר אמר יוסף. The famine began just as Joseph had said. It was necessary for the Torah to repeat "as Joseph had said;" Joseph's interpretation of Pharaoh's dream was proven true especially after the seven years of plenty were followed by the famine. Had the famine not commenced at that time, people would have said that the seven years of plenty had nothing to do with Joseph's forecast.

2Another reason for the Torah telling us the events in this manner maybe that the Torah emphasised a different aspect of Joseph's forecast. After seven years of abundant surplus it is most unusual to feel the onset of a famine immediately. The Torah therefore tells us "as Joseph had said," i.e. that the years of plenty would be completely forgotten, that people would eat but not be satisfied during the years of famine. This lack of satisfaction with the food one ate became evident already at the beginning of the first year of the famine.