This, in turn, has led to rise in power costs and in greenhouse gas emissions, a report by independent think tank on water issues Pacific Institute said.

Pacific Institute president Peter Gleick said: "This 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."

Natural gas and hydropower have been the top two sources of power in the US state, with the latter contributing 18% of the total energy requirements.

However, three years of drought has cut down hydroelectricity’s contribution to 12%, with natural gas becoming a more prominent and an expensive player.

According to the report, the total additional energy cost to the state’s electricity users during the six years of recent drought was $2.4bn.

"If the current drought persists, water flowing to drive hydroelectric turbines will continue to shrink and expensive and polluting natural gas will become even more of a factor in the electricity production game," the report observed.