[LINK] Not just oil: US hit peak water in 1970 and nobody noticed

[Kim Holburn]

http://arstechnica.com/science/news/2010/05/not-just-oil-us-hit-peak-water-in-1970-and-nobody-noticed.ars

> The concept of peak oil, where the inaccessibility of remaining  
> deposits ensures that extraction rates start an irreversible  
> decline, has been the subject of regular debate for decades.  
> Although that argument still hasn't been settled—estimates range  
> from the peak already having passed us to its arrival being 30 years  
> in the future—having a better sense of when we're likely to hit it  
> could prove invaluable when it comes to planning our energy economy.  
> The general concept of peaking has also been valuable, as it applies  
> to just about any finite resource. A new analysis suggests that it  
> may be valuable to consider applying it to a renewable resource as  
> well: the planet's water supply.
>
> The analysis, performed by staff at the Pacific Institute,  
> recognizes that there are some significant differences between  
> petroleum and water. For oil, using it involves a chemical  
> transformation that won't be reversed except on geological time  
> scales. Using water often leaves it in its native state, with a  
> cycle that returns it to the environment in a geologic blink of an  
> eye. Still, the authors make a compelling argument that, not only  
> can there be a peak water, but the US passed  this point around  
> 1970, apparently without anyone noticing.
>
> They make their case based on three ways in which water can run up  
> against limits on its use. The first is peak renewable water, for  
> sources that rapidly replenish, like river basins or snow melt. The  
> classic example here is the Colorado River where, for most years  
> since 1960, essentially no water has reached the ocean. Although  
> actual water use is governed by a series of interstate and  
> international agreements, these simply serve to allocate every drop  
> of water. Similar situations are taking place in other river basins,  
> such as the Jordan.
>
> The second is what they term peak nonrenewable water, as exemplified  
> by the use of aquifers that replenish on time scales that make them  
> closer to a finite resource. (This issue is so well recognized that  
> it has a Wikipedia entry.) At the moment, the Ogallala and Central  
> Valley Aquifers in the US, along with a number in China and India,  
> are being drained at a rate that far exceeds their recharge.  
> Ultimately, usage will necessarily peak and start dropping, as it  
> gets harder to get  access to the remainder. Eventually, these water  
> supplies will tail off to something in the neighborhood of their  
> recharge rate.


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Kim Holburn
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