It would be nice to have finer control over evacuations and emergency planning. For example: if a tsunami warning or a type of disaster that will affect a significant portion of the city and gives plenty of preparation time, it'd be better to have citizens evacuate from the city via highways/buses, trains, ships, and etc. For disasters that have more precise impact or too short time to leave the city, it'd be more appropriate to have citizens shelter in-place, like for tornados, earthquakes, and thunderstorms.
That could be presented in-game as a series of buttons: Leave City, Shelter In-place, Seek Shelter
It'd also help to have control over which populaces to alert so that the rest of the city isn't unnecessarily disrupted. Like being able to issue District-specific warnings as well as Citywide warnings.
A set of additional preparative policy measures should also be introduced to help improve the chances of survival in specific disasters, such as retrofitting structures to tolerate stronger earthquakes, and subsidized survival/Red Cross training (which could also help slightly improve the overall well-being of the citizenry). An option to command existing mass-transit resources to aid in evacuation should also be available.