Intensified by climate change, the current 20-year arid period is one of the worst on record, with wide-ranging effectsThe Enterprise Bridge passes over a section of Lake Oroville that is nearly dry in 2014 in Oroville, California. The region is in the grip of a 20-year megadrought, research suggests. Photograph: Justin Sullivan/Getty ImagesWhen Ken Pimlott began fighting US wildfires at the age of 17, they seemed to him to be a brutal but manageable natural phenomenon.