I think that this is an interesting question and it is clearly a topic that will bring several different answers.

I will give you my opinion and be interested in seeing comments.

Yes, it did rain on earth before the flood and since there was sun prior to the flood, there were also rainbows.

The reasons:

1. God created the earth and all climatic cycles at the beginning of time. Generally, rain is created in at least two ways. First, orographicly where precipitation (rain) is created by the action of wind and temperature change created where mountains are present (e.g. Oregon Coast). Second, by convection hot air rises and through atmospheric action creates precipitation. The sun, seasons, day and night and atmospheric pressure all work together to make this happen. I believe that God created this process in the beginning and rain occurred as a result of the natural process. The earths atmospheric balance is one of the fabulous wonders that God has given us to experience.

Rainbows are cause by sunlight and moist air. Both were present before the flood. On the rainbow, Gen. 9:13 says I set my rainbow in the cloud, and it shall be a covenant between Me and the earth. And it shall be when I bring a cloud over the earth, that the rainbow will be seen in the cloud. (MKJV). It doesnt say that the rainbow is new nor does it infer that clouds were never present before the flood. God had cleansed the earth of sin with water and was using the rainbow as a water related feature that was noticeable and would remind man of Gods power and promise. The rainbow had been there before but had no such symbolic meaning.

More on atmospheric cycles. During the flood the seasonal cycles were severely interrupted. It was a year that probably had no real summer. Thats why God promised that the seasons would continue forever which was a parallel promise to the rainbow as a symbol (Gen. 8:22).

2. Scripture does not say that it had not rained. Many a VBS teacher or pulpit preacher has said so but it doesnt appear that God did. In Gen. 2:5 For the LORD God had not caused it to rain on upon the earth, and there was no man to till the ground. But there went up from the earth a mist and watered all the face of the ground&. (MKJV). Then in verse 7 it says that God formed man from the dust. It appears that the no rain situation was before man was created or at least was before man was banished from the garden. I understand that this may be debatable. But I feel that scripture provides no real evidence that the earth was watered by mist for approximately 1000 years.

God said that he was going to flood the earth. He did this to cleanse sin from the earth. I just cant find where the scripture says that it had never rained. In Hebrews 11:7 the faith of Noah is commended because he moved with fear when warned of things not yet seen. I believe that it was the flood that is the subject here. Noah had seen rain, but he hadnt seen a flood that was so large the it would totally destroy the earth

3. It wasnt just rain that made the flood, in fact it was probably mostly NOT rain. It says that the fountains of the deep were opened and it rained. The opening of the fountains of the deep was a natural miracle that was created. God made it flood in a way that man had never seen before, and, by Gods own word, will never see again. He made water and rain to flood the earth.

4. It doesnt make God greater if it had rained before the flood. Gods power shown through the unfathomable cycle of climate, seasons, the firmament, he is no greater if we believe that he created rain and a rainbow at the time of the flood. It doesnt make Noah have any more faith because he had to believe that God would flood the earth. Lot had to believe that God was serious in his threat to destroy Sodom, Gomorrah and the cities of the plain.

P