Mercury: FIRE authorities and farmers are bracing for a punishing summer after yet another winter of below-average rainfall. Parts of Tasmania’s East Coast are now so dry that nothing short of a torrential downpour will alleviate the extremely high bushfire risk. The Bureau of Meteorology’s soil dryness index is one of the tools used to predict the length and severity of the fire season — and this year the prediction is not good. At zero the soil is fully saturated, with any …