http://eelriver.org/2015/03/the-impacts-of-californias-drought-on-hydroelectricity-production/
The Pacific Institute just released a report that evaluates how California’s drought has resulted in less energy produced by hydroelectric dams and a greater reliance on the more expensive process of burning natural gas.
The current severe drought has many negative consequences. One of them that receives little attention is how the drought has fundamentally changed the way our electricity is produced. Under normal conditions, electricity for the state’s millions of users is produced from a blend of sources, with natural gas and hydropower being the top two. Since the drought has reduced the state’s river flows that power hundreds of hydropower stations, natural gas has become a more prominent player in the mix. This is an expensive change.
According to the Institute’s report, between October 2011 and October 2014, California’s ratepayers spent $1.4 billion more for electricity than in average years because of the drought-induced shift from hydropower to natural gas. In an average year, hydropower provides around 18 percent of the electricity needed for agriculture, industry, and homes. Comparatively, in this three-year drought period, hydropower made up less than 12 percent of total California electricity generation. The figure below (Figure 6 from the new study) shows the monthly anomalies in state hydropower generation in wet and dry years, and the severe cuts over the past three years.