The fall's from 7.9 million tons in 1916 to 4.9 million tons in 1917 that is 3 million tons.Hmmm... so it appears the Italian coal supply remained relatively stable until 1917, the massive drop in imports then I'm assuming possibly due to the resumption of USW?
UK coal production fell by about 8 million tons between 1916 and 1917, that is from 256.4 million tons to 248.5 million tons in 1916. That could be the reason for the reduction in Italy's coal imports.