Ancient Egyptain civilization heavily relied on the Nile for sustenance. This included flooding of the Nile river and the various irrigation systems (redirecting water, sometimes 'far') that were built to support agriculture in and around the Nile basin. The river was also used as a transport channel, eventually bridging Lower and Upper Egypt in the 'unification'. Since the reliance on the Nile was so pervasive in all walks of life, changes in conditions could considerably hamper efforts at maintaining a stable harvest and distributing it throughout Egypt.
If rainfall was low in one particular year (or several years) this could impact transport of crops along the Nile, irrigation of surrounding fields, crop yields, etc. and also lead to conflict. Here is one example where the authors suggest that a decrease in rainfall led to the fall of the Old Kingdom.
Furthermore, different pharaohs and rulers in ancient Egypt had vastly different temperaments. This impacted their social policy. Poor planning together with unexpected climate conditions (and more) could certainly have caused or contributed towards widespread famine or even local famine due poor to distribution.
Aside: In the modern age, conflicts arising from water disputes are widespread. In one National Geographic (April 2010) edition on Water the authors attributed 30+ wars in the middle-east to be water related in the 20th century. Just for interest: note that Yaakov (and family) came to Egypt and lived in the land of Goshen (partly in the Nile delta) with enough grazing land to support their livestock (despised but tolerated by Egypt, see Bereishit 46:31-34)