The long-term average streamflow in the Colorado River at Lee’s Ferry, Arizona is 13.5 million acre feet. From 1579-1598 the average was 11 million acre feet.
For the last two decades, the average has been 12.4 million acre feet. The reduction has been largely due to diverting huge amounts of water across the Continental Divide to the Colorado Front Range.
Even with the diversions, the average streamflow has been considerably higher than the 1579-1598 drought, but that doesn’t stop Scientific American from simply making up fake statistics.