This letter appeared
in South American Explorer, 31, May 1992.
Loren McIntyre's claim about the flow of the Amazon [Magnum Bunkum, South American
amounts to the proverbial argument about comparing apples and oranges.
compare the Amazon's annual supply of fresh water to the total amount of fresh
water on Earth, including that held by ice caps and glaciers, ground water, lakes,
soil moisture, atmosphere, biota, and rivers. Orange:
To compare the Amazon's
annual supply of fresh water to the world's annual supply of fresh water that returns
to the sea from the land. McIntyre's quote of the article by LaRiviere in Scientific
American, 261(3), Sept. 1989, in support of his statement that the Amazon
contains less than 1/10000 (0.01%) of the total fresh water on Earth is an
The same article states that the World Resources Institute estimates that 41,000
cubic kilometers of fresh water return annually to the sea from the land. UNESCO
(Studies and Reports on Hydrology No. 25, 1978) lists the mean annual discharge
of the Amazon river at its mouth at 220,000 cubic meters per second, based on a discharge
of 157,000 measured at the Obidos narrows. This translates into 6,900 cubic kilometers
returned annually to the sea, or roughly 1/6 of the total volume of fresh water
returning to the sea. This is an orange. Viewed in this light, there is no popular
misconception to correct.
Victor Miguel Ponce
Mouth of the Amazon river at Macapa, Brazil