b, The intertropical convergence zone (ITCZ). The ITCZ was defined asregions that received a mid-summer (January (turquoise colour gradient)or July (red colour gradient)) mean monthly total rainfall of >20 cm,for the period 1979–2017. Where both January and July had rainfall of>20 cm, we show the measurement from the month with the largest total.The ITCZ is a strong predictor of the distribution..