With an average annual runoff of 70 million acre-feet (maf) and a demand of 30 maf,1 California’s water supply problem is a spatial and temporal one; two-thirds of the natural runoff occurs north of Sacramento while two-thirds of the population and the major share of irrigated agriculture is south of that point.2 Over 80 percent of the precipitation occurs between November and March, which is the period of lowest use.3 The maldistribution is mitigated by several water storage and delivery systems, the largest of which are the federal government’s Central Valley Project and California’s State Water Project. Both export projects utilize the Sacramento-San Joaquin delta east of San Francisco Bay as a “pooling place” from which northern California (Sacramento River) waters are exported southward (Figure 1).