Farm revenue in California dropped by more than $9 billion last year as the drought forced farmers to scramble for water and crucial commodities declined in price, according to data released by the state and federal governments Tuesday. The U.S. Department of Agriculture’s economic research service said farm income totaled $47.07 billion last year in California. That compared with a record $56.61 billion in 2014. All through the drought, which has cut off deliveries of surface water supplies to large swaths of the Central Valley, farmers have been able to increase revenue by pumping more groundwater and switching to high-dollar crops such as almonds.