Have you been following the California dam that might be failing? The largest, tallest dam in the country is leaking and might have a catestrophic failue. They have evacuated around 200,000 people down river. Several entire cities, one with a population of 65,000, and vast areas of farmland. They are now saying it could be several weeks before people are allowed back in.
How could you prepare for something like that? Obviously the basics... having go bags for family members, essential papers copied on thumb drives and stored with a family member out of town, enough cash on hand or available in an emergency fund account to stay in a hotel, but I think this particular case goes much deeper.
Everyone these people know and deal with on a regular basis are also being displaced. Their jobs are ceasing to exist for the duration of the evacuation... or permenantly if the dam fails. Any livestock will likely die is unattended for two or three weeks of the evacuation. If the dam fails, everything they own and everything around them will be gone.
Most of us will never have to face such an extreme event. A tornado might wipe out part of a town, but the rest of the town could be unscathed. A hurricane can wipe out a city, but the evacuation will only be for a few days before you know for sure whether you'll be able to go home or not. Same thing with a wild fire or chemical spill... it is a short term situation and then you know whether you can go home or start recovery. This thing has people in limbo. Stuck with no answers. The psychology of it must be as tough as the financial and logistical impacts on families.
If you are downstream of a dam, do some research and check on it's condition and any evacuation plans. Your local emergency managment office will likely have that information available. The Army Corps of Engineers has a great interactive website for the National Inventory of Dams. Here in Virginia, we have just over 2900 dams, and 468 of them are of a "high" hazard potential.
Keep those folks affected by the California situation in your thoughts and prayers. They are going to have a tough time of it for a while, even if the dam is stabilized.