I have to say, that I absolutely love this picture Your realistic style is amazing and it really fits the scene and the many details like the firey sun, the fire around Celestia's horn and the dark colour of the mountains add a lot to the apocalyptic feeling The composition is also cleverly done, since the diagonal horizon adds a lot to the chaoticness. I think it's great, that you made her mane look more like actual hair than her normal mane, because it fits the tone of the image better and it doesn't look to much like bubble gum to me I think the objects, that those high waves are splashing against should be better visbile, because the way it is, it looks like their splashing against nothing, but that's just a minor nit-pick and you did a fantastic job overall
lol i see the seen from Lord of the Rings: the Two Towers, see the falling towers are there and the water is from when the Ent's broke that wall and the tree tops sticking out are Ents. Celestia's just supervising to make sure the good guy wins.
Celestia and Luna have just defeated Discord, ending his forever kingdom of chaos. The flood is one the many, many aspects of his keeping Equestria in an "eternal state of unrest and unhappiness" (per RoH, S2E1) that they must now cleanse and purify. So Celestia starts the process of "creating harmony for all the land" (per FiM, S1E1) by producing the very first sunrise in the very first dawn (ditto). Later that same first day Luna will step forward to "begin the night" (ditto) by causing the very first moonrise, and with that harmony's creation will be complete, Equestria finally starting to recover.
Here's one: First time trying to raise the Moon after Nightmare Moon's banishment. Screwed up the orbital mechanics, caused ridiculously huge tides that flooded whole towns, and now after teleporting everypony out she's struggling to fix this mess. It took her a decade before she got it right.