What weather added to the people's trembling as they sat in the square in Ezra 10?

Answer: Heavy rain

On the twentieth day of the ninth month the people sat trembling over the matter and because of the heavy rain.

“So within the three days, all the men of Judah and Benjamin assembled in Jerusalem, and on the twentieth day of the ninth month, all the people sat in the square at the house of God, trembling regarding this matter and because of the heavy rain.”— Ezra 10:9 (BSB)