Charles Ellicott Commentary 2 Samuel 21:9

"And he delivered them into the hands of the Gibeonites, and they hanged them in the mountain before Jehovah, and they fell [all] seven together. And they were put to death in the days of harvest, in the first days, at the beginning of barley harvest." — 2 Samuel 21:9 (ASV)

The beginning of barley harvest. —This was immediately after the Passover (Leviticus 23:10–11), and therefore around the middle of April. The autumn rains began in October, so Rizpah’s watch must have lasted about six months. She spread the sackcloth like a tent to form a rough shelter during her long watch. The term water dropped should be understood as water poured; the original word is used for melting or flowing and thus signifies heavy rain. It was not until these rains began (which were probably somewhat earlier than usual) that the people were assured of Divine forgiveness, and therefore the bodies of the executed were left unburied until then.