Wuwei
If all of the water in the atmosphere rained down at once, it would only cover the ground to a depth of 2.5 centimeters, about 1 inch.
Additionally, because only 1.7% of the earth’s water is stored underground,12 there is not nearly enough water in groundwater storage beneath the earth’s surface to account for the amount of water necessary to flood the entire earth to the extent described in the Bible.
Simply put: there is not enough water in Earth’s atmosphere to raise the ocean’s levels over an inch, much less to cover Mt. Ararat with water from 40 days of rain. There is simply not that much water in the system.
Thus, in order to even entertain the possibility of a worldwide flood, one has to bypass all laws of physics, exit the realm of science, and enter into the realm of the miraculous, which many biblical literalists are willing to do. It is hypothetically possible that, say, the polar ice caps melted.
This could raise the ocean levels beyond the 2.5 centimeters that all the earth’s atmospheric water could were it to all rain down, but even then the thaw would only slightly affect the world’s coastlines. Additionally, all scientific evidence points to larger polar ice caps in recent history, not smaller.