If I were asked to pinpoint the cause of the collapse of the Old Kingdom in Egypt, I would have to point my finger at the environmental changes in that time period. This collapse was marked by the weakening of the monarchy and allowed provincial governors to assume royal power over their region. This breakdown of the Old Kingdom, however was caused by the sudden and unexpected reduction in the Nile floods the persisted over two or three decades. As we have seen the evidence for in class, a severe famine gripped the region, and it is this that in turn paralyzed the central political institutions
We can clearly see this lapse in flood levels, shown by sediment cores collected from the area. These low floods were related to a larger scale global climatic cooling which reduced the amount of rainfall in Ethiopia and East Africa. In Iceland, researchers have detected a transition from birch and grassland vegetation to arctic conditions in about 2150 BC. This correlates with a shift to drier climate in south-eastern Europe c.2200 – 2100 BC. Also, the reappearance of oak at White Moss, UK, suggests fluctuating wetness in around 2190 – 1891 BC. In Italy, drier conditions are found around 2200-1900 BC in Lake Castglione. Dry spells have also been detected as far away as Western Tibet at Lake Sumxi.
The most interesting, and relatively recent discovery, was made when scientists made a high-resolution study of dust deposition from Kajemarum Oasis in north-eastern Nigeria. The study conclusively revealed that a pronounced shift in atmospheric circulation occurred in around 2150 BC. This data indicates that an abrupt, short-lived event of cold climate led to less rainfall and a reduction of water flow in a vast area extending from Tibet to Italy. This of course, led to the catastrophic events that we see depicted in studies from the Egyptian Old Kingdom.
From year to year, the long-term variations in Nile floods may be beyond the perceptions of people living at that time, without the use of accurate measuring devices, but the effects are surely felt. The volume of flood discharge varies wildly in episodes, which range from decades to hundreds of years. Furthermore, there is the impact of freak years where the floods can be disastrously low or high. The Nile, today and during the prosperous times of the Old Kingdom, can be regarded unquestionably as the source of life in Egypt. Ironically it seems, the Nile had just a big a hand in destroying the State it had built.
An interesting article on the topic (even if it is a bit old) http://www.geotimes.org/apr05/feature_NileFloods.html