By the Grace of God and Guru,
Here is a mantra for rain:
""Nikame nikame nah parjanyo varsatu",
this is a very powerful mantra . It is chanted with strong conviction, "The clouds have to form, the clouds have to form, it has to rain, it has to rain!" And a sankalpa - firm resolution is made for it to rain in a particular place," this "is a mantra
from the Vedas... the Yajur Veda.
It is chanted to bring rain to a particular area, " says Karunamayi Amma of www.karunamayi.org in Her book "The Nectar of Jnana" pages 206,208