During heavy rains or flooding

Living underground, unless your underground house is built sort of like a submarine and completely waterproof, you likely wouldn't want to be there if there were 5 to 10 feet of water running by on the surface, especially if you were living under flat lands or in a flood plain underground. So, one way would be to seal up your home underground during a flood and move out onto the surface of the earth either into a tree house that you build for this or a small structure you build on stilts higher than the floods have ever been in your area.

However, because of global warming and global Climate change, floods in some areas are going to be 2 or 3 times as bad as they were ever before like we saw in Houston this year as well as the problems in Florida, Puerto Rico and throughout the Caribbean. So, extreme flooding could occur literally any year in the future in this area once again, just like the devastation of a Hurricane Sandy could devastate the east coast again or worse any year now too with increased evaporation off the ocean from warming oceans above normal temperatures before 2000 and ever increasing winds also caused by increased water and air temperatures on a year around basis worldwide, even though some areas are going to experience colder temperatures than ever too because of polar vortexes slipping off the north and south poles. (for example, the north pole has completely melted off for a few days each the last two years). This hasn't happened on the south pole yet. But, when it does Antarctica will be dry land mostly when this happens since it doesn't snow there anymore mostly because it is too cold to do that anymore. It just blows the snow that is already there around.

So, as you can see, I'm proposing a solution that would be better than the path we are presently on which is: COMPLETE HUMAN EXTINCTION!

This century or next.