Joseph told Pharaoh that his dreams came from God telling him to prepare for seven years of plenty followed by seven years of famine.  The task of Pharaoh was to find a wise and honest man to put some of the abundance of the years of plenty away to provide for the years of need and avert a terrible tragedy.  So who would you believe on rainfall in that region – Joseph or Obama? 

Rainfall in the Mediterranean Basin is influenced by ocean surface temperatures in the tropical Pacific and the north Atlantic.  Because of the importance of Nile River to the Egyptian civilisation water levels have been measured for 5,000 years and recorded for more than 1,300.  The ‘Nilometer’ – known as al-Miqyas in Arabic - in Cairo dates back to the Arab conquest of Egypt.  The Cairo nilometer has an inner stilling well connected to the river and a central stone pillar on which levels were observed.  The exterior of the stilling well can be seen in the photo below.  The Nilometer remained useful until the 20^th century when major dams changed the Nile River flow regimes.       

Source:  WaterHistory.org

Water levels varied from ‘hunger’ at 12 cubits (a cubit is approximately half a metre) through abundance at 16 cubits and to disaster at 18 cubits. 

D. Kondrashov and colleagues collated a record of Nile River water levels spanning from 622AD to 1922AD.   They calculated the mean of high water levels at 18 cubits.  This suggests that life in ancient Egypt might best be described as lived on the edge.  Perhaps not surprising given Joseph’s source of information – is that they found a strong 7 year signal in the data.  The record shows increasing water levels over the past millennia and a prominent spike towards the end.  There were signals of variability – more or less flooding – on a 256 year regime.        

Pacific variability has major impacts on global hydrology and can be followed in fine detail over the Holocene.

Source: Tsonis 2009

Moy et al (2002) present the record of sedimentation shown above which is strongly influenced by ENSO (El Nino Southern Oscillation) variability. It is based on the presence of greater and less red sediment in a lake core. More sedimentation is associated with El Niño. It has continuous high resolution coverage over 12,000 years. It shows periods of high and low ENSO activity alternating with a period of about 2,000 years. There was a shift from La Niña dominance to El Niño dominance that was identified by Tsonis 2009 as a chaotic bifurcation – and is associated with the drying of the Sahel. There is a period around 3,500 years ago of high ENSO activity associated with the demise of the Minoan civilisation (Tsonis et al, 2010). Red intensity exceeded 200 – for comparison the red intensity during the 97/98 El Nino was 99. It shows ENSO variability considerably in excess of that seen in the modern period.

Whatever the cause – global hydrological variability - extreme drought, extreme floods and extreme temperature changes such as has not been seen in the 20^th century - will occur again.

The solution – such as it is – is to build prosperous and resilient communities.  As Joseph tells us – to avoid catastrophe in the times of need requires a wise and honest person to manage things in the times of abundance.