Joseph told Pharaoh that his dreams came from G0d 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. The variability in ocean surface temperature year to year, decade to decade, century to century result in persistent regimes of droughts and floods. Because of the importance of Nile River flows 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 20th century when major dams changed the Nile River flow regimes.
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 climate and can be followed in fine detail over the Holocene. ENSO (El Niño Southern Oscillation) has an influence on global surface temperatures, Australian, American, Indian and African rainfall and Atlantic cyclones.
Source: Tsonis 2010
Christopher Moy and colleagues presented the record of sedimentation shown above – it is a high resolution proxy strongly influenced by ENSO variability. It is based on the presence of more or less red sediment in a lake core and provides a very long term insight into global hydrological variability. More sedimentation is associated with El Niño. It has continuous coverage over 11,000 years. It shows periods of high and low El Niño 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 Anastasios Tsonis as a chaotic bifurcation – and is associated with the drying of the Sahel. There is a period around 3,500 years ago of high El Niño activity associated with the demise of the Minoan civilisation. Red intensity exceeded 200 – for comparison red intensity during the 97/98 El Niño 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 20th 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.