Now i am thinking of the pakistani flood that has taken place recently. this is a good example of why Noah's flood was global and did take place. NO ONE puts a destructive local flood into their identity, religious works, or makes it a life changing event. Katrina is another example, the flooding there did not do anything to change america's identity, nor did they incorporate it as a major historical event that changed their civilization or made them put it into their religious writings.
If you don't think that the Pakistan flood is a life changing event for many people, particularly the thousands who have died or lost members of their family, and also for the millions who have been displaced and are now suffering from injury, hunger or disease, and that it will continue to affect their lives for many years to come, and that a great deal already has been and will continue to be written down to record the event and its consequences, there is something seriously wrong with your ability to comprehend reality.
Furthermore, you obviously fail to understand that any people who suffered such catastrophes thousands of years ago would have had little or no idea of the size of the earth and their place in it. To them, the local area was "The Whole World", so any local catastrophe would have been considered "global" (not that many of them would have thought of the world as an actual globe) and most people outside the area of catastrophe would have had little or no idea that it had even occurred. If anyone later heard a story of a great "global" catastrophe, they would have no way of knowing where it actually happened, that it maybe happened in some other valley and not where they lived. That's obviously very different to today where everyone knows that the recent floods only affected certain areas of Pakistan.
Today we find evidence in rocks and soils of large local floods in the past. In some cases, such as the floods that occured in North America as the glaciers melted at the end of the ice age, they were huge floods, far greater than anything witnessed in recent history. But there is no evidence in the soils and rocks of anything like a single global flood. If there were ever a single global flood (leaving aside the question of where all that water would come from and then go to) there would be evidence in soils and rocks of the same age all around the world. There is just nothing like that.