Rain of Acid

Area 
Droplets of acid rain from the sky onto the area, causing 1d-1 acid damage per second to all within it. Characters and creatures under the rain of acid take damage on their own turns; if less than an entire second is spent in the affected area, damage is halved (round down). 
The spell can only be cast out of doors. Armor protects in the usual fashion. A shield with a DB of 2 or better can be held overhead to block the droplets, but it may take damage (p. B484). This requires two hands and a Ready action, and succeeds automatically in protecting the character once the shield is readied upwards, but this unreadies the shield from its normal protective functions! 
In addition, acid rain eats objects away at the rate of 1 HP every 10 seconds; the object’s DR protects it completely for 3 seconds per DR. This includes buildings.

Duration: 1 minute. 
Base cost: 3. Same cost to maintain. 
Prerequisites: Magery 2, Create Water, and Create Earth.

Item 
Staff. Usable only by mages.  
Energy cost to create: 1,200.