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Nile Flood
Wed Oct 06, 2004
Listen in RealAudio 
According to Greek historian Herodotus in the 5th Century B.C.: "Egypt is the gift of the
Nile," Hi, I'm Bryan Yeaton, and this is The Weather Notebook.
Herodotus wondered why the Nile floods every summer, adding several centimeters of
fertile soil. Normally, he thought, floodwater is fed by snowmelt coming off of the
mountains in the spring. But the Nile starts in the south, and in Egypt, the farther south
you go, the hotter it is. So melting snow couldn’t be the answer.
So how did Herodotus explain the flooding of the Nile? Simple. It doesn't flood. What
appears to be a flood in the summer is just the regular flow of the river. He believed
that, during the winter, strong winds somewhere to the south blew so hard that they
made the sun come to a complete halt. And since it’s just sitting there, there’s more
heat to evaporate waters of the Nile so that the river becomes lower in the winter. Now
when the wind dies down in summer, the sun moves on, things go back to normal,
and then comes the flood. An interesting theory, but wrong.
The Nile flood normally begins in August and ends around October. The floods are
mostly due to monsoonal rains, some thousands of miles away in the highlands of
Ethiopia and from as far south as even Rwanda. And some of the water comes, sorry
Herodotus, from the snowcapped Mountains of the Moon on the Uganda-Zaire border.
Henry Stanley, of Dr. Livingston fame, rediscovered the Mountains of the Moon, which
had been referred to in the 2nd Century CE by Greek geographer Ptolemy. Stanley,
however, called them by their native African name: Ruwenzori, or Rainmaker.
The Weather Notebook is a production of the Mount Washington Observatory, with
underwriting provided by Subaru of America.
Today's Links
Mountains of the Moon
http://ca.essortment.com/wherearethem_rlsu.htm
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