rain on (someone or something)
1. To pour or fall on someone or something from above in a rain-like shower. Dirt and debris rained on us following the explosion. Bombs continued raining on the city from above.
2. To cause some liquid, loose substance, or multitudinous small objects to fall down in a shower on someone or something. In this usage, a noun or pronoun is used either before or after "down." The castle defenders rained boiling oil on the attackers below the ramparts. The dark clouds began raining down hail on us halfway through the hike. The other kids started raining down snowballs on us from the other side of the yard.
3. To give or bestow something on someone in abundance. In this usage, a noun or pronoun is used either before or after "down." The boss has been raining praise on Janet all week for the work she did. People across the country are raining down condemnations on the prime minster for his handling of the crisis.
rain (up)on someone or something
[for rain, or something similar] to fall on someone or something. (Upon is formal and less commonly used than on.) The ashes from the erupting volcano rained on all the people fleeing the village. It rained on the fields until they were flooded.