Figure 4: K-means station clusters for each period, onset (a), peak (b), and retreat (c).
The relative humidity is then averaged over the stations in each cluster to obtain cluster indices for the three periods and a time series of their standardized values are shown in Figure 4. The Although the actualabsolute relative humidity varies between each cluster, but the figure shows that the they all have similar temporal variability (not shown). All three periods exhibit an upward trend from ~1988 through 2012, which corresponds to the upward trend found in the Sahel rainfall index (Janowiak 1988).
