Extreme Drought and Water Supply Management in California

The geological record contains extreme droughts beyond those seen in historical hydrologic records. For California, the geological record contains several extreme droughts the last few thousand years. Two of these droughts are 120–200 years long, with mean annual streamflows between 40% and 60% of the historical mean. This study synthesized a 72-year historical record for a drought of this character, having a mean flow of 40% of the historical record. This hydrologic time series was used as input to an economic-engineering optimization model of California's water supply system (CALVIN). The model allows exploration of how California's water management system might respond to such an extreme drought and provides preliminary estimates of economic costs and effects of such a drought on water operations and demands. The overall results show the importance of management flexibility and adaptation in response to extreme stresses on water systems. Results also illustrate the physical ability of extensive, diversified, and highly intertied water systems with heterogeneous water demands to economically respond to such extreme stresses. The study provides a different approach to climate change studies, focusing on observed past changes in climate from the geologic record rather than downscaled general circulation model results to provide hydrologic scenarios.