Was the Flood Local or Global? The scope of the flood
While this question may seem innocuous and obvious to modern readers, there is a problem inherent with how we even phrase this question. Modern people read this question and instantly are thinking about scientific things. They want to measure the flood and its impact, they want to describe the flood in terms of geological phenomenon, its geographical extent, its effects on biology, and its meteorological processes.
The problem with this kind of thinking is that in the original story these elements are mere details in the background, the story itself presents the flood as a literal historic event that is presupposed, while the narrative is much more concerned and centered upon the impact the flood has on humanity, and God's redemptive act through Noah. The details are foregone conclusions. This leaves modern readers to adjust the background details to their pre-existing scientific ideas, which may or may not be supported by the text itself. This is best seen in the language that describes the flood.
The first evidence of this is illustrated best by asking the question whether the flood was global. Even the idea of a globe (a geographical descriptor of the whole plant earth, referring to its spherical structure) is non-existent in the text. Instead kol eretz and ha eretz (translated as whole earth, the earth) have a much more localized and grounded meaning in Hebrew. Every timekol eretz is used in Genesis, it is speaking of a limited area. Eretz itself is actually better translated as soil or ground. (see Robert Alter's translation of Genesis)
When God creates ha shamayim and ha eretz in Genesis 1 (this is a Biblical merism, by the way), the text is not talking about "planet earth" and "space", it is quite literally saying that God created everything between the ground and the skies. It presupposes that everything else that exists was created by God as well (because He is the only creator), but for the sake of men and women - to whom the story is being written, it limits the scope of its descriptions to the things that we are directly familiar with that is the ground and the sky. In the same vein there is no mention of when or where angelic beings or the spirit realm were created, because they don't fall within the purvey or purpose of the story, they're simply presupposed to have been created by God, without any more details given.
When Genesis says that all the earth was covered, including the mountains, the scope of the language is by definition limited and local. Saying in English that all the soil was covered in water is very different from saying the whole earth was covered in water, although some may miss the distinction. Interestingly enough, even the quote from 2 Peter 2:5 talks in the same way - it doesn't say that the the planet earth was destroyed, instead it says that the LORD destroyed the world of the ungodly, limiting the scope of the destruction to that part of the world which was under the rule of ungodly men.
The Effects of the Flood
What then was the effect of the flood? Essentially, God reset His creation. He destroyed the world He created to cleanse it of sin, and cut off the corruption of men and Nephilim.
But wouldn't God have had to flood the entire planet, to achieve His goal of wiping out humanity? Simply put, no. The idea that humanity was spread out before the flood is born out of a mis-understanding of the text and how it relates to pre-history and current scientific theory about human development. The text clearly indicates that all of humanity after the flood descends Noah's family alone, therefore any human settlements would naturally be post-flood, and post-babel.
There is nothing to lead us to believe that humanity (or animal life) had spread over the entire globe, or wasn't otherwise concentrated and localized (actually, the story in Genesis regarding the tower of Babel seems to imply at the very least the human custom of staying closely together may have been both cultural and normative during this time period).
In this case, a severe, but local flood would have been enough to wipe out all of mankind, because all of mankind was centralized around the Garden of Eden and surrounding areas.
Other Theories about the Genesis, and the Flood's Effects and Reach
There are, of course, other theories about the flood's impact, some of which try to align themselves in varying degrees to contemporary scientific accounts of prehistory and human development. Some Biblical interpreters would postulate that Adam and Eve were not the first humans, rather the first human's with consciousness and therefore having souls (nephesh).
These commentators assert that evolution happened for millions of years before God chose Adam and Eve - and that these other proto-humans (and their descendants) who would have populated the earth would not have needed destruction by the flood because God was only destroying wicked humanity.
While it can be understood why some commentators feel the need to mesh scientific understanding with Biblical interpretation, the above remains to me an example of how quickly things can get completely outside of the text if we are not careful with our hermeneutics. The above theories proved very popular 60 years ago before the human genome project confirmed 1 common ancestor pair for all human beings.
About our modern biases
Asking then, if the flood was global presupposes modern interpretive bias by introducing concepts and language into the discussion that aren't actually present in the Hebrew text of Genesis. But as modern people we are so scientifically minded, that we automatically interpret things through a scientific lens.
Because of these linguistic insights, some Bible scholars have tried to re-examine their modern-biased readings of the text, in favor of a more literal interpretation, based on the literal Hebrew meanings. To quote Dr. Gavin Ortlund in the article that was provided as a source by the questioner,
At the very least, allowing for the possibility of a local flood should not be written off as circumventing the “obvious meaning” of the text. For me, as far as I am aware, it is an effort to take seriously the meaning of the text, which involves what the original author meant for the original readers to take from it in its original context. In fact, what inclines me to imagine a huge but non-global event here in Genesis 6-8 is the text itself (the meaning of the Hebrew terms and phrases as they occur elsewhere in the Old Testament, for instance; or the sequence of Genesis 8:4-9).
While it may be in vogue in our culture to look at everything through the lens of scientific understanding and fit our theological framework into our cultural worldview, it's important to remember that Genesis itself was written as a polemic against the predominate cultural and continues in the same function today.
We shouldn't be surprised if Genesis does not always fit neatly with our cultural beliefs, especially when considering the cultural bias against Scripture and belief in Christ predominant in the West.
Conclusion
While I remain open to the geographical scope of the flood myself, the idea that a regional flood rather than a worldwide global event can only come from acquiescence to scientism, rather than simple hermeneutics, is erroneous. As is the idea that somehow a local flood would necessitate God lying or misleading people in regards to His actions. A local flood interpretation of the text is wholly congruent with the text itself and may fit better with the general scope and flow of the narrative.
As always, we should strive to have our minds teachable, and open to the correction that the study of scripture provides.
