There are several synonyms that can be used instead of the phrase "annual Nile occurrences". One option is to use the phrase "regular Nile events", which conveys the same idea of regular happenings along the river. Another possible synonym is "yearly Nile phenomena", which suggests a more scientific or natural perspective on the occurrences. Alternatively, the phrase "annual Nile happenings" could be used, which is a more straightforward and colloquial way of referring to the recurring events. Regardless of the synonym chosen, the important thing is to convey the idea of repeating, predictable events along the Nile.