I have been considering building one of those emergency dome shelters for just this purpose (including shelter). One of the advantages of them is that if you don't get them built ahead of the disaster, if you have the simple & minimal equipment, you can build one in a day or two. They are stable in earthquakes, & I suspect with extra soil dumped over them & planted with something like clover that has an abundant root system, they could be incredibly handy for those in Tornado Alley who also have high water tables that prevent you from having a basement. Maybe not all that useful for those in hurricane areas, but I have no experience there.

The equipment consists of sandbags (number depends on size of the shelter), a shovel or two, a roll of barbed wire, & something to use as a door. And a string & 2 sticks or large nails.

Tie one of ends of the string to one stick or nail. Measure 4 or 5 ft, then tie the other stick or nail there. Punch one of them into the ground & use the other end to scribe a circle in the ground. Or use the scribing end to measure & some flour or lime, etc to mark the circle.

Start digging to mark the edge of the circle clearly, & put the soil in the sand bags as you go. Lay the filled sandbags at the outer edge of the circle, end to end, leaving a gap for the entrance.

As soon as you have one circle of bags on the ground, cut 2 lengths of barbed wire & lay it on top of the bags, in 2 rings. The wire stabilizes the bags & keeps them from shifting. Lay another ring of bags on top of the wire & repeat. There must always be 2 rings of wire between each layer. You would probably want to put in a few short pieces of plastic pipe between a few of the bags for ventilation as you're stacking them.

With each circle of filled bags, work them inward just a bit, gradually building a dome.

Depending on climate, some people have covered the dome with a single sheet of heavy plastic, and then covered the dome with 8-12" of soil & planted it to stabilize it.

Others have applied a layer of concrete over the bags to form a smooth impervious surface. Some add a bit of dry concrete to the soil put in the bags to firm them up (esp in the sandy desert, I would suspect).

As you build, you can leave or carve out sleeping platforms, or include shelving as you stack the bags. How about a small fireplace with a chimney hat sticking out? (I don't know what those things are called.) And a good, sturdy door.

For a visual, you can go to the CalEarth site at http://www.calearth.org/emergshelter.htm. These photos look like the domes were built on flat ground as samples, but then you would have to bring in soil to fill them.