Pageviews last month

Tuesday, 11 December 2012

Missing the rains down in Africa--and other likely causes of the Seven Bad Years

Counter In an earlier post, I mentioned in passing what may have caused the 14 years of changed climate reported in Genesis chapters 41-47. I thought my readers would like a more extended coverage of this topic.

Prior to the building of the Aswan Dam in the 1960's, the annual flooding of the Nile from June to September was the make-or-break season of the year for the entire Egyptian civilization. The flood level varied from 12 cubits to 18 cubits at the Delta, with the most desired level right between those two extremes.

What made the flood so vital to life in Egypt were two things: the water itself, and the rich sediment it carried. The water extended out toward the limits of the floodplain, soaking the soil enough to supply in one watering the moisture needed to germinate the crops. The sediments were left behind as the flood receded, enriching the soil with nutrients.

There are two ways that agriculture in Egypt could be devastated: one by too much water, and one by too little water. Too much water would rise high enough to wash away the farmers' homes, scour the fertile silt from their fields, and dampen the remnants of the previous year's harvest, damaging their seed and leaving them no grain to subsist on until the next harvest.

Too little water would mean unflooded fields, unable to sustain a crop until harvest.

Now, the scenario in Genesis is 7 years of plenty, during which a huge surplus of crops was stored up. This was followed by 7 years of famine, during which the surplus was eaten. This scenario doesn't fit very well with the too-much-water theory, which would have washed away or at least dampened the surplus grain. The too-little-water theory is a much better fit with the evidence.

Now, what could cause the twice-normal bumper crops for 7 years running? The most likely answer is a biannual flooding of the Nile, allowing two crops a year to be grown.

This is the usual Nile annual cycle:

Akhet (June-September): The Flooding Season. 
No farming was done at this time, as all the fields were flooded. Instead, many farmers worked for the pharaoh (king), building pyramids or temples. Some of the time was spent mending their tools and looking after animals.

Peret (October-January): The Growing Season. 
In October the floodwaters receded, leaving behind a layer of rich, black soil. This fertile soil was then ploughed and seeded.

Shemu (February-May): The Harvesting Season. 
The fully grown crops had to be cut down (harvested) and removed before the Nile flooded again. It was also the time to repair the canals ready for the next flood.

In order to fit in two crops a year, the seasons would have had to be shorter in duration, with each flood following hard on the previous harvest:

Akhet I (July-August) - The First Flooding Season.

Peret I (September-October) - The First Growing Season. 

Shemu I (November-December) - The First Harvesting Season. 

Akhet II - the inundation (January-February) - The Second Flooding Season.

Peret II (March-April) - The Second Growing Season. 

Shemu II (May-June) - The Second Harvesting Season. 

Now, interestingly enough, there already are two annual flood cycles on the Nile: one on the White Nile, and one on the Blue Nile.  Flow on the White Nile starts to climb in March and peaks in October; flow on the Blue Nile and other Ethiopian tributaries begins to pick up in June and peaks in August. Thus the Blue Nile flood is superimposed in the White Nile flood, causing a huge fluctuation in the annual flow of the Nile downstream of Atbara, especially so because, at its peak, the Blue Nile contributes nine times the volume of water than the already-flooded White Nile.

Now, what could possibly cause these two flood cycles to spread far enough apart to occur opposite each other on the annual calendar? Furthermore, it had to have been something that happened only once, as the Nile has never again experienced this sort of 14-year cycle.

The obvious answer is that it had something to do with the melting of Ice Age glaciers in the high mountains of Ethiopia.  Prior to this, Egypt would have only received one flood a year, from the White Nile. Rainfall in Sudan was probably considerably higher than it is now, but still seasonal. Thus Egypt was used to a single annual increase in Nile volume spread out over half the year, from say June to January. But one year the glaciers in Ethiopia began to melt, with just a small outflow the first summer, say from June to August. This, on top of the already rising waters of the White Nile, provided a gentle watering of the river valley suitable for the cultivation of orchard crops such as dates, figs, and pomegranates. As colder weather returned in September, the glaciers stopped melting and the floods receded long enough to allow the orchards to dry out and harvesting to occur.

Meanwhile, the rains in Sudan and Uganda--perhaps even on down into the Southern Hemisphere, if the Nile was longer back then--continued to swell the White Nile to another peak in January, soaking the ground for the planting of spring crops like flax, barley, wheat, and spelt (according to Exodus 9:32, none of these were ripe yet in April). These were just nicely grown to full size for harvesting in May before the water level rose again in June.

Now, let's say it took seven years for the Ethiopian glaciers to melt. It was also about this time that the Sahara was turning from green to brown, so the rainfall in Sudan probably dropped considerably as well. Wind patterns keep moisture-laden air from reaching the Ethiopian highlands where it could precipitate to fill the Blue Nile tributaries. The level of the Nile began to drop after the 7th year, and just kept getting lower and lower. It would half-heartedly flood each summer, but not enough to reach the fields--the fruit trees survived the drought with greatly diminished harvests, but the grainfields remained too parched to even plant, year after year.  Finally, after another seven years, wind patterns shifted around to once again bring those rains down in Africa, and one June the Nile began to rise to pre-drought levels.

Well, this is just one scenario. Another possibility is that the seven bad years were caused by double floods that kept the fields too wet to plant until there wasn't enough time left to harvest before they were flooded again. I don't know which is the more likely, or better fits the evidence; but at least I've fleshed out one theory for the origin of the Seven Good and Seven Bad years of Genesis 41-47.

One last comment: the Nile is now able to support a greatly increased population due to irrigation schemes that allow most of inhabited Egypt to grow two crops a year. The downside is that the Aswan High Dam has ended all the benefits of the annual inundation.

In that sense, every agricultural year in modern Egypt is equally both Good and Bad.

UPDATE 12/12/12: This just in:
Matt Konfirst, a geologist at the Byrd Polar Research Center, speaking at the annual meeting of the American Geophysical Union, presented evidence of a devastating drought in Sumeria about 4000 years ago. He estimates it lasted about 200 years. I would propose that he is off by a factor of 20.

UPDATE 03/23/13
Well, according to research reflected in the map at this website, there were no Ice Age glaciers in Ethiopia. In fact, no tropical glaciers are thought to have existed. So, back to the drawing board--either for me, or for them. Probably for AIG--this website clearly shows that there are equatorial glaciers in Africa now; surely there also were then.
"Despite Mount Kilimanjaro’s location in the tropics, the dry and cold air at the top of the mountain has sustained large quantities of ice for more than 10,000 years"

1 comment:

One comment per viewer, please--unless participating in a dialogue.