In the beginning it isn't clear what has happened although from the conditions the narrator, Mia, finds herself in, we could guess it's the aftermath of a hurricane.  When the book takes place is also vague, I believe purposely.  Although it has to be in the future, we can easily surmise it isn't by much.  The world Callea describes is credible given the underlying assumption of the string of natural disasters and the repercussions that would stem from them.