If so, the period of no rain was brief, and we must conclude that it rained before the flood. If so, the preflood rivers would have been mere trickles. A third possibility is that the mist, lakes, and rivers were supplied by water forced up through porous regions of the earth's crust from the high-pressure subterranean water described on page 93 . A humid atmosphere would supply heavy dew each day during the cool morning hours. Vegetation would thus receive a steady supply of water, especially vegetation with large surface areas.
Rainbows form when raindrops refract sunlight.
This suggests that rainbows were first seen after the flood, and there was no prior rain. Other interpretations, however, are possible. Perhaps rainbows were visible before the flood, but after the flood God simply associated His promise with rainbows. This would be similar to the promise that a married couple associates with their wedding ring. Rings existed before the wedding, but the ring on a person's finger carries a special significance afterwards.