This is something special.
Addicting gameplay.
I would suggest changing a bit of the randomness of card draws. It might work better as an actual 'deck' of cards. Dealt from a stack than shuffled etc. So you would have a deck of
fire 1, 2, 3, 3, 4, 4, 5, 6
hurricane 1, 2, 3, 3, 4, 4, 5, 6
earthquake 1, 2, 3, 3, 4, 4, 5, 6
flood 1, 2, 3, 3, 4, 4, 5, 6
for example. So, you would never get a hand of flood 1, flood 1, flood 1, etc..
You could even add modifiers like a real deck building game. Something like, each time you obliterate 10 cities, you can choose a bonus, with a condition.
Removes all 1 disasters from the deck, but 1 cities always grow to 3.
Add a Hurricane 7 to the deck, but 7 cities spawn 2s.
Coastal Cities take double damage from Hurricanes, but none from Fire.
Something I found not fully explained is that order is important. For example, if you use a Hurricane on a 7, and a Fire next, and the fire is barely touching the 7, the 6 it turns into may be to small to touch your fire. Very tricky.
Really solid game even without any changes.