This script changes a dry landscape to a wet one. I scripted my tutorial from here: https://www.flickr.com/groups/gimpusers/discuss/72157623477454455/
Copy it into the scripts folder from GIMP, you will find it then under Filters → Light and Shadow → Rainy Landscape.
It doesn’t have many options, because you can change them afterwards in the layers menu (CTRL-L).
If you like it, hug someone.