Hydropower and natural gas are the principal sources of electricity for California’s millions of users. But California’s hottest and driest drought in recorded history, from 2012 to 2016, shifted the sources of energy for electricity with adverse economic and environmental consequences. The prolonged period of extreme drought reduced the river flows powering hundreds of hydropower stations in the state. Natural gas replaced the lost hydroelectricity, at high cost to both consumers and the environment.

This report is a comprehensive assessment of the costs to California of lost hydroelectricity during the four years of drought from October 2011 to the end of September 2015 (the official California “water year” runs from October 1 to September 30).

• The drought at the time of publication is more severe than past droughts. Hydropower generation is at 10.5 percent of total electricity generation during the four-year period from October 2011 through September 2015, compared to 13 percent during the 2007-2009 drought and the 18 percent average in non-drought years. For the 2015 water year hydropower was especially low, providing less than seven percent of total electricity generated in-state.

• This analysis finds that during the four years ending September 30, 2015 (the end of the 2015 “water year”), the added economic cost to California ratepayers of reduced hydroelectricity production was approximately $2.0 billion.

• In addition to the direct economic costs of replacing hydroelectricity generation, there are environmental costs associated with the additional combustion of natural gas, including increased air pollution in the form of nitrous oxides, volatile organic compounds, sulfur oxides, particulates, carbon monoxide (CO), and carbon dioxide – the principal greenhouse gas responsible for climatic change. Additional combustion of fossil fuels for electric generation led to a 10 percent increase in the release of carbon dioxide from California power plants.

Appendix 1A: Data Sources for Section 1: Drought and Domestic Water Shortages

Appendix 1B: Spreadsheet: Drought-Impacted Public Water Systems

Appendix 1C: Spreadsheet: State Reports of Household Outages, Aug 8 2016

Appendix 2A: Spreadsheet: Drought Charges

Appendix 2B: Spreadsheet: Affordability Analysis

Appendix 3A: Tribal Salmon Fishery Data

Website: California Drought

Impacts of California’s Ongoing Drought: Agriculture

Impacts of California’s Ongoing Drought: Hydroelectricity Generation

Impacts of California’s Five-Year (2012-2016) Drought on Hydroelectricity Generation