Not only have consumptive uses north of the Delta exceeded exports for many years, the outflows have not collapsed as some claim. What these figures do not show is the timing of these various diversions and outflows. Our better understanding of and regard for fish needs underlines the importance of timing.And here's the picture that we've all been waiting for [click for larger]:As you can see, south of Delta exports average somewhere in the 5.5MAFY range. That's large but only relative to in-delta diversions. Upstream consumptive use is much greater.
Addendum: This figure is Figure 7B in the Final Report [PDF] of Delta Vision.
But note one thing, in-Delta diversions were FIRST; upstream diversions were SECOND; and south-of-Delta exports were LAST. Even small diversions can be blamed for "breaking the smelt's back," and the south of Delta interests were "last in time, last in right."
On a related note, PB also sent this analysis from a partisan:
On March 31, 1977, the CVP had 3,035,300 acre-feet of water stored in its northern California reservoirs. This point is still considered the driest on record and yet the CVP was able to deliver to its SOD ag service contractors 25% of their contract supply and some additional water to help protect permanent crops.State Senator Cogdill (eastern San Joaquin Valley) makes similar claims of a "regulatory drought" caused by 3-4MAF of "environmental takings."
In 1991, the fifth year of a protracted drought, the CVP was again forced to curtail its deliveries to SOD agricultural customers to only 25% of contract supply. Under those true drought conditions, CVP storage ran approximately 37% and 44% of capacity, respectively.
On March 31, 2009, northern CVP storage stood at 5,033,200 acre-feet or 61% of capacity [and CVP deliveries are penciled in at 10%]. The difference between these “dry” periods is attributable entirely to changes in the regulatory constraints placed upon the CVP since the last natural drought.
On August 4, 1989, the National Marine Fisheries (NMFS) issued an emergency interim rule listing the Sacramento winter-run Chinook salmon as threatened under the federal Endangered Species Act (FESA). Since that time, other FESA listings combined with implementation of the Central Valley Project Improvement Act and federal Clean Water Act through the State Water Resource Control Board’s Water Quality Control Plan have resulted in the reprioritization of at least 3,200,000 acre-feet of CVP and State Water Project water [every YEAR!] for environmental purposes.
This volume does not include potential impacts that may result from the longfin smelt’s recent listing under the California Endangered Species Act nor the soon to be released NMFS revised biological opinion for salmon, steelhead, and green sturgeon.
 ~500,000 af Shasta cold water pool; ~400,000 af Trinity River restoration flow; ~800,000 af Sacramento River and Bay-Delta restoration flows; ~400,000 af wildlife refuge supply; ~1,090,000 af 2009 FWS Biological Opinion; ~100,000 af additional Water Quality Control Plan costs. Many of these numbers may be better or worse depending upon hydrological year type.
Bottom Line: Seems like there's some space for a north-to-south market in water trades :)