This needs two parts. Really, lot of steps, but easy.
○Previous tutorial : fav.me/d77tezx
As my friend requested, here is tutorial on how to paint lot of water, with mouse.
If you don't know how to draw water (sorry, i can't help you here), you can use existing lineart for help. Also, i'm using free human sketch from this wonderful person lucynickbakura.deviantart.com/…
Free to use line arts
Painting flood part 2 is next--water details, foam, background details and how-to-chage color of water.
Post what you have done so far in comments
○ Ask for any help or suggestion