Guest post by Mike Jonas
9 Sep 2020
News today is that the highest floods in over a century are threatening Sudan’s ancient pyramids (not to be confused with Egypt’s pyramids):
The authorities in Sudan are trying to protect the country’s ancient pyramids from flooding as heavy rains have caused the nearby River Nile to reach record-breaking levels.
Now I do understand that one flood does not a cycle make, but the news immediately made me think of the NASA report of 2007 that found a link between the Nile water level and solar activity:
NASA Finds Sun-Climate Connection in Old Nile Records
Long-term climate records are a key to understanding how Earth’s climate changed in the past and how it may change in the future.
Now, however, a group of NASA and university scientists has found a convincing link between long-term solar and climate variability in a unique and unexpected source: directly measured ancient water level records of the Nile, Earth’s longest river.
“Since the time of the pharaohs, the water levels of the Nile were accurately measured, since they were critically important for agriculture and the preservation of temples in Egypt,” she [Joan Feynman of NASA’s Jet Propulsion Laboratory] said. “These records are highly accurate and were obtained directly, making them a rare and unique resource for climatologists to peer back in time.”
A similarly accurate record exists for auroral activity during the same time period in northern Europe and the Far East.
The researchers found some clear links between the sun’s activity and climate variations. The Nile water levels and aurora records had two somewhat regularly occurring variations in common – one with a period of about 88 years and the second with a period of about 200 years.
So what causes these cyclical links between solar variability and the Nile? The authors suggest that variations in the sun’s ultraviolet energy cause adjustments in a climate pattern called the Northern Annular Mode, which affects climate in the atmosphere of the Northern Hemisphere during the winter. At sea level, this mode becomes the North Atlantic Oscillation, a large-scale seesaw in atmospheric mass that affects how air circulates over the Atlantic Ocean. During periods of high solar activity, the North Atlantic Oscillation’s influence extends to the Indian Ocean. These adjustments may affect the distribution of air temperatures, which subsequently influence air circulation and rainfall at the Nile River’s sources in eastern equatorial Africa. When solar activity is high, conditions are drier, and when it is low, conditions are wetter. [My bold]
From the WUWT solar reference page, it does indeed appear that solar activity has been heading lower for a while, though the data appears to be not quite up-to-date:
So the question is: Are the unusually high Nile Floods caused by this lower level of solar activity?
To try to answer the question, I plotted rainfall for Sudan:
[Annual precipitation anomaly 1979-2019, requested lat 10N-20N lon 25E-35E, from NOAA. Hopefully I have accessed and charted the data correctly. I couldn’t find a longer record.]
Well, it doesn’t look much like a cycle to me, but then 40 years would not be long enough for one to show up. However, it does look like there was a big step-change from 2013 to 2014. Any ideas on what could have caused that? Could it have been because of a change in solar activity?
The IPCC has not managed to shed much light on this issue. Their latest Africa Report shows that the third IPCC assessment report predicted “Threats of desertification and droughts to the economy of the continent“, but the fourth report predicted “Potential impacts of extreme weather events (droughts and floods)“. The fifth report said “A continued warming in the Indian-Pacific warm pool has been shown to contribute to more frequent East African droughts over the past 30 years during the spring and summer seasons. It is unclear whether these changes are due to anthropogenic influences or multi-decadal natural variability.” but then (maybe just as the 2014 rains were starting?) they went on to say that “Projected increases in heavy precipitation over the region have been reported with high certainty [..]”. Looks like the IPCC were hedging their bets when the climate wasn’t following their script. Africa Renewal didn’t worry too much about the hedging. A few years later, under the scary heading Global warming: severe consequences for Africa, they reported that “Every bit of additional warming adds greater risks for Africa in the form of greater droughts, more heat waves and more potential crop failures.“.
My guess is that the 2013-14 step-change is fortuitous, and that it is a part of a cycle that would normally have taken several years but this time happened to occur very sharply. The cycle itself is more likely to be driven by the Indian ocean (or maybe the Atlantic) than solar activity. Ocean cycles would have a more obvious effect than solar activity on precipitation in places like Sudan over decade+ timescales, but solar activity would show up on century+ timescales. Also that the combination of ocean and solar cycles would be significant. But that’s only a guess.