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Re: E-M:/ USGS report: How Much Water is Lost in Great Lakes Basin?

Enviro-Mich message from Rane L Curl <ranecurl@umich.edu>

On Tue, 27 May 2008, Rita Jack wrote:

How Much Water is Lost in the Great Lakes Basin?

"We found that irrigation and livestock had the largest losses compared with
total water withdrawn from the Great Lakes basin" said Kimberly Shaffer,
hydrologist with the USGS and author of the report. "Of the total water
withdrawn for irrigation, 70-100 percent was lost to the basin"

A fact sheet titled "Consumptive Water Use in the Great Lakes Basin" by
Kimberly H. Shaffer, is available at http://pubs.usgs.gov/fs/2008/3032/

The cited report gives estimates of the total consumptive use of water from the Great Lakes Basin of about 4,224 million gallons per day (Mgal/d), of which 28% is via public water supplies, 26% via thermoelectric power generation and 20% via irrigation. These values must, however, be judged in terms of the total water budget for the Great Lakes Basin. Therefore, to put it in perspective, I list the following values for a base average water budget from Mcauley_nov2004.pdf :

Total Basin precipitation:   474,200  Mgal/d
Total Basin evaporation:     299,300  Mgal/d
Total Basin runoff           142,400  Mgal/d

The amount of water lost to the Basin by consumptive uses is therefore about 0.91% of precipitation, and about 1.4% of natural evaporation (from water bodies and evapotranspiration).

The total water budget is what affects lake levels, an aspect of particular concern, and these are changed by the accumulation of small percentage differences in annual precipitation, evaporation and runoff. Therefore small differences due to climate variability and consumptive uses can have large cumulative effects, However consumptive should not be looked at in isolation, but rather in terms of the overall management of the water budget of the Basin.

--Rane L Curl

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