Not Related to YA Books But It's a 4.2 Kiloyear Event

This post is not related to books; at least, not to the usual books I've been featuring here. Books are associated with this, nonetheless, since I wouldn't have been able to piece together the sort-of answer to the question that has been bothering me since yesterday.

If you are following my Twitter account then you must have read something along the lines of me watching a Discovery Channel feature: Why Ancient Egypt Fell and my frustrations to the HOW and the WHY. To update you on what I'm talking about, this feature discusses the fall of the Old Kingdom approximately 4200 years ago. It tells of the end of the rule of the last king of the Old Kingdom in Egypt after a 94-year rule1, which coincided with a drought so severe that approximately 70+ settlements along the Nile were reduced to about four. The cause of the fall of the Old Kingdom was also connected to the fall of the Akkadian Empire, changes in the Indus Valley civilizations and collapse of some cultures in China.
The 22nd Century BC Drought (it was a hundred years long) was the cause (not the Aryans) but my question was why and how the drought came to be in the first place. That drought is called the 4.2 kiloyear event. One could put the word aridification in there somewhere2. It mirrors the 5.9 kiloyear event which led to the desertification of the Sahara, once a vast expanse of lush rainforest. There was also a mention of Bond Event 3 which refers to the "glaciation of northern climates" and it follows a 1-500 climate cycle. Let's just that there was a massive global climate changes in those events (there was also the 8.2 kiloyear event) and I still am not any closer as to why it happened. Humans were not as destructive to the environment as we are now. So why and I'm still not clear on the how. I've read somewhere that the 4.2 kiloyear aridification event was caused by an asteroid impact somewhere but the study results were not conclusive. If anyone finds the answers to my question...3 Notes:
1. A period which I found dubious since I didn't believe for a second that the pharaoh would've lasted that long given the history of Egyptian monarchy. I found myself right after a few turns of research journals which stipulated a 60+-year rule and different calculations between different calendars and such.
2. It's not all about drought and drying up but it was also a glacial period for northern places.
3. I don't even know why I'm writing this here in a book blog. This must be the result of my frustration of not knowing something. As you may have deduced, I've been carrying a torch for ancient civilizations and history and had once had the hope of being an archaeologist but alas life throws you a curveball (and different decisions at crucial times i.e. college applications) and my interests are now satisfied with reading scholarly articles and watching Discovery Channel specials.