One glaring reason to consider a global flood over a local one in the Genesis account would be the necessity of saving the land animals and birds. This would seem to be an unnecessary labor for Noah and his family, if the flood were a local phenomenon. One author even suggests that Noah was kept in ignorance of the true extent of the flood and only believed it would be global. Notice:
It would require real energy and faith to follow Noah’s example and build other Arks, but it would have required neither of these to pack up a few things and migrate. There is nothing Noah could have done to stop them except disappearing very secretly. Such a departure could hardly act as the kind of warning that the deliberate construction of the Ark could have done. And the inspiration for this undertaking was given to Noah by leaving him in ignorance of the exact limits of the Flood. He was assured that all mankind would be destroyed, and probably supposed that the Flood would therefore be universal. This supposition may have been quite essential for him.
If others would repent, why would it be necessary to build additional arks? If Noah’s preaching were successful, God’s judgment would have been canceled or at least been delayed or curtailed to only a portion of mankind. Moreover, this doesn’t speak very highly of the honesty of God. Why would he deem it necessary to deceive Noah? Does virtue arise out of deception? Nevertheless, concerning the necessity of saving the land animals and birds Rich Deem has this to say:
“Some animals are indigenous only to the Mesopotamian area. More importantly, it would have taken hundreds of years longer to replace the fauna if everything had been wiped out and had to migrate back in. In addition, Noah would have had a huge problem replacing his herds.
“If the Flood was local, why would birds have been sent on board? They could simply have flown to a nearby mountain range. Most birds (other than a few migratory birds) have a very localized territory. They would have been killed in the local flood, since they are not designed to fly long distances. Certainly archaeopteryx was not a strong flyer. Hummingbirds would drop dead in 20 minutes or less. One thing that you will notice when there is a strong rain is that birds do not fly. Flying in heavy rain is not easy. They would have sat on their perches until the water drowned them.”
There have been many local floods throughout history, and God never again called anyone to save the animals indigenous to that area. The Genesis Flood is the single exception. If God didn’t account it necessary to save the animal kingdom from local floods, why would he make an exception in Noah’s day, if, indeed the flood were local? Moreover, Deem’s perspective demands that no animal species could have migrated to other parts of the earth by the time of Noah, and he presumes that indigenous species to the Mesopotamian valley were always so. Animal behavior, at least in some respects, changed after the Flood (Genesis 9:2). Even if, Deem’s perspective concerning indigenous animals is correct, why would God be required to save a particular breed from extinction, when history proves this was not an overriding concern of his?
Concerning Noah’s herds and the length of time it would take to replace the animal kingdom either locally or globally, God is the one who causes men or animals to multiply. Time is of little consequence to him, for he causes all things to work out according to his original plan. As for Noah, it was an inconvenience to wait for his herds to replenish, but this didn’t keep him from enjoying the vegetation. He did become a vinedresser (Genesis 9:20). Moreover, he could have occasionally enjoyed meat from his growing herds, or he could have hunted for meat among the clean wild animals, and certainly the fish were plentiful. So, an inconvenience on Noah’s part does not demand the necessity of a local flood.
 Arthur C. Custance, The Nature of the Forbidden Fruit; (1958), page 18