When Zeus' son Sarpedon meets his fate, Zeus expresses grief for his dead son by causing blood to rain (Iliad 16: 459-461). In Egypt, the function of rain is replaced by the Nile which fructifies the soil. Accordingly, the Biblical Plague of Blood (Exodus 7: 19-25) is the Egyptian equivalent of the bloody rainfall in the Iliad.

Ch.VII Further Observations on Homer - The Common Background of Greek and Hebrew Civilizations (1965 [1962])