Rain

Rain was a form of precipitation that came from rain clouds. Petrichor was the smell of dust after rain. (TV: The Doctor's Wife) When the Judoon used an H2O scoop to transport the Royal Hope Hospital to the Moon, the rain went up around the hospital, while no precipitation fell anywhere else. It rained again on the Moon when the hospital made the return trip. (TV: Smith and Jones)

As Amy Pond implied, it rained a lot in Scotland; when it was raining in a car park, she deducted that it must be Great Britain. (PROSE: Apollo 23) It also rained a lot of Grått, forcing the Tenth Doctor to employ an umbrella. (COMIC: The Whispering Gallery) The presence of rain clouds told the Second Doctor that he, Jamie McCrimmon and Zoe Heriot had arrived in English during the summer. (TV: The Invasion)

When Earth was returned to its proper location in the Sol system after the Daleks had relocated it to the Medusa Cascade, it rained a lot for a while afterwards due to atmospheric disturbances. (TV: Journey's End)

The Doctor's sonic screwdriver was capable of causing rain via atmospheric excitation. (COMIC: Death to the Doctor!, Mudshock)

Clara Oswald's tears turned telepathic snowfall into salty rain on Christmas 1892. (TV: The Snowmen)

Sally Sparrow first met Billy Shipton in the basement of Wester Drumlins while it was raining. After Billy got sent back by the Weeping Angels, she met an older Billy during the same rain. Billy died when it ceased raining. (TV: Blink)

The Sun of Fire and Rain was one of the "Five Suns in the Sky" according to the Aztecs. (TV: The Aztecs)

According to the legends of thwe Gonds, when the Krotons invaded their planet, they "caused a poisonous rain to fall", killing hundreds of them. (TV: The Krotons)

Predictions
Several species and objects were able to predict rainfall.

Bazoolium went cold before it was to rain. (TV: Army of Ghosts)

After the Pyroviles entered the Pompeii area, the soothsayers, the augurs and the haruspex inherited psychic powers and could predict crops and rainfall with absolute precision. The Tenth Doctor claimed that always knowing this would make life boring. (TV: The Fires of Pompeii)

The damages of rain
As Lucius Petrus Dextrus put it, "rain pleases the soil". (TV: The Fires of Pompeii) Rain was necessary to sustain plant life. The Tenth Doctor once said, "A little rain never hurt anyone." (TV: Gridlock) This, however, was most certainly not true.

According to Blon Fel-Fotch Passameer-Day Slitheen, while it was raining, "visibility was low" — this could lead to car accidents. (TV: Boom Town)

Excess rain could cause flooding. (TV: The Invasion) Acid rain, rain that was unnaturally acidic, could "melt" forests. (TV: The Doctor, the Widow and the Wardrobe)

A species resembling rain could easily cut through human flesh. When the human colonists arrived on its planet, they drank the water, and were consequently killed by it. The rain would keep on falling until at least one or two people were killed. (PROSE: Pitter-Patter)