Analysis: in drought, more Delta exports go to urban use

Governor Jerry Brown announced an executive order on April 1 mandating 25% statewide urban water conservation. This action is essential to conserve water in reservoirs to get through an extended drought. It might even help maintain minimum instream flows in rivers and estuaries so that endangered fish populations have a chance of surviving the drought.

Many people have cited statewide averages of 80% of California’s developed water supply going to agriculture, and 20% to urban use, derived from DWR’s estimates for 2001-2010 in the California Water Plan. Some conclude that urban conservation won’t make a significant difference in 2015 demand on rivers and the Sacramento-San Joaquin Delta. But these numbers are different in critical droughts such as 1977 and 2014-2015, when summer agricultural diversions are curtailed. And even in normal years, the Ag/urban percentages of diversions from individual river basins are different from statewide averages. For Delta exports, urban use has been greater than 20% for decades.

Since the State Water Project came online in the 1970s, urban water agencies have used ever an ever-increasing amount of Delta exports. The urban share of Delta exports has increased even more in the critical drought of 2014-15. While deliveries from the South Delta pumps to many agricultural contractors in the San Joaquin Valley were cut off in 2014, urban deliveries are continuing. Allocations of the State Water Project and Central Valley Project show that in 2015, about 48% of Delta exports are going to urban water agencies, 46% to agricultural water agencies, and 6% to wildlife refuges. Use of Delta exports by urban water agencies could actually be greater than use by agricultural water agencies this year.

Conclusion

Reducing urban demand on the Delta will significantly reduce total demand for Delta exports. The governor’s mandated urban conservation measures are essential. Mandatory statewide conservation will help avoid catastrophic conflicts between urban needs and the environment, should the drought continue into 2016 and beyond. Rapid implementation of these conservation measures could also help prevent major extinctions of endangered fish populations, including critically endangered pelagic fish in the Delta, including Delta smelt, Longfin smelt, and Winter run Chinook salmon.

Here’s some more information about the 2015 allocations by the State Water Project and Central Valley Project, planned Delta export operations, and how these estimates were derived.