Genèse 7:4

For, behold, I give you space of seven days; if they will be converted, it shall be forgiven them; but if they will not be converted, after a time of days yet seven, I will cause rain to come down upon the earth forty days and forty nights, and will destroy all bodies of man and of beast upon the earth.

כי לימים עוד שבעה, G’d commanded both Noach and the animals to enter the ark already seven days prior to the onset of the deluge in order to assign to them their various accommodations and in order to get them used to their change in diet, especially the flesh eating beasts which had to adjust to a vegetarian diet. According to the Midrash (Sanhedrin 108) Metushelach had died during these days and G’d suspended the decree until after the days of mourning for him had expired. He had been a righteous man and it was no more than appropriate that his passing should be noted with appropriate eulogies and mourning rites. We know that these eulogies were spread over a period of seven days from Genesis 50,10 where, even though Yaakov had already been mourned for 70 days in Egypt prior to the transfer of his remains to the cave of Machpelah in the land of Canaan, he was eulogized again. We had already demonstrated that according to the data provided by the Torah Metushelach must have died at the time the deluge commenced.

אנכי ממטיר, G’d did not make mention of the fountains of the earth bursting forth as it is a well known fact that this usually happens as a corollary to unusual amounts of rain falling on earth. The fact that the rainwater softens the earth’s crust, enables these subterranean wells held in check by the earth’s crust to burst forth without restraint. These additional waters then flood the surface of the globe. After all, as we explained already during the report of the creation, it is the natural tendency of water to inundate the dry areas of the globe. From a scientific perspective, all we have to remember is that the specific weight of water is lighter than that of earth, so that if allowed free reign, earth would always sink to the bottom of the water. The deluge therefore was not an unnatural event but it was a return to what had been natural until G’d had given a directive at the beginning of the third day that the waters concentrate in a single area to enable the earth to become visible. G’d had imposed unnatural restraints on the waters at that time, something that our sages have called an agreement made by Him with the waters, to comply with G’d’s commands when the need would arise.