Persistent drought slashed output from hydro generation and cost California’s consumers US$2 billion over the last four years, Oakland-based water policy think tank the Pacific Institute calculates.

In 2015, low reservoirs slashed hydroelectric output from its usual 18% share of California’s electricity to as low as 7%. To make up for the missing generation, the Bee reports, utilities have had to turn to fossil fuels, increasing greenhouse gas emissions from the sector by 10%.

Things may look better this year, with a strong El Niño delivering more precipitation than in several recent winters. However, most climate simulations forecast long-term drying over most of the U.S. southwest, including California.