Those among the humans who had been taught by the Serpents of Wisdom, those who were wise and travelled the world, were very in tune with the energies of the world. They sensed that something very bad was about to happen, hundreds of years before it happened.
In preparation, they went to the leaders of their great civilisations, the city states, the technologically advanced, and advised them to prepare for these events. Whether it was the wandering wise or their own sages and mystics bringing them warning, many listened.
In many places across the world, large caverns were dug out deep under great cities or in the mountains, and filled with anything survivors might need. Often, they contained their sacred writings and ancient histories.