Albert Barnes Commentary 2 Samuel 21:10

"And Rizpah the daughter of Aiah took sackcloth, and spread it for her upon the rock, from the beginning of harvest until water was poured upon them from heaven; and she suffered neither the birds of the heavens to rest on them by day, nor the beasts of the field by night." — 2 Samuel 21:10 (ASV)

Dropped - Rather, this means “poured,” the proper word for heavy rain (Exodus 9:33). The “early rain,” or heavy rain of autumn, usually began in October, so Rizpah’s devoted watch continued for about six months. We learn how rare rain was during the harvest from 1 Samuel 12:17–18 and Proverbs 26:1.

The reason the bodies were left unburied, contrary to the law in Deuteronomy 21:23, was probably that their death was an expiation for the guilt of a violated oath. They were to remain exposed until the rain fell, which would be the assurance that God’s anger was appeased and the national sin was forgiven.

Birds of the air... beasts of the field - It is well known that in the East, when a camel in a caravan dies, for example, vultures instantly flock to the carcass .