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Lake Mead plummets to unprecedented low

Glenn MacGrady

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Just because some very downstream reservoirs are full doesn't mean the total river system storage capacity, as a series-of-reservoirs whole, can't be at historically low levels. If it is.

Low water levels can be a function of increased water demand or of drought. Over the decades, it's obvious that the Colorado River has been tapped for significantly ever-increasing water demands, primarily by California and Arizona, and also that there have been periodic regional droughts, which may or may not be due to interglacial global climate warming.
 
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For the Colorado, and many western rivers, the decline in snowpack over the last 70 years has had predictable consequences. While eastern Colorado is dry the Colorado Rockies are, or were, a different story, with up to 60 inches of rain/snow precipitation in some mountain areas.

In most of the West, snowpack has decreased since the 1950s, due to earlier melting and less precipitation falling as snow. The amount of snowpack measured in April has declined by 20 to 60 percent at most monitoring sites in Colorado.”

There are still “wet” years, but the trend is towards decline, so in spring the water management agencies capture as much as allowed for storage in reservoirs, and hope it is sufficient to tide them over until the following spring.

Not just the Colorado; many western rivers are dependent on melting snowpack. In 2018 parts of the Rio Grande essentially dried up into a series of desiccated puddles.

https://sourcenm.com/2021/09/18/mem... Rio Grande,been ripping with spring snowmelt.

That wasn’t the first time in recent memory parts of the Rio Grande ran dry. In 2000-ish the Rio Grande in the Big Bend area ran dry when Mexico abrogated water release agreements from the Rio Conchos.
 
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