Annual airborne pollen counts xi(t) for 120 sites from 2003 to 2016. (a) The time series expressions of xi(t) for 120 sites in eight regions. Red lines indicate the mean value in each region. (b) Time–space diagrams of xi(t) in each term [t − t + 1]. Orange: increased state, Blue: decreased state, Green: unchanged state, White: no data.