West Africa rainfall decomposition. Illustration of ‘time scales decomposition’ for west African box shown on the map, for the July-August-September season. The numbers on each graph are the percent of variance of the full observational timeseries explained by each of the timescales. The determination of the trend component is as dscribed in Figure 2. The “natural variability” remaining after subtracting the trend component, is filtered into a low-frequency, or decadal component, and a high frequency, or interannual component. The difference between the sum of these numbers and 100% is the covariance between the interannual and decadal components. As in Figure 2, the precipitation data is taken from University of East Anglia’s Climate Research Unit version 2p1 (UEA-CRU2p1: (Mitchell & Jones 2005)). Data and maps available at IRI Time Scales map room available at: http://iridl.ldeo.columbia.edu/maproom/Global/Time_Scales/. Note that the observational dataset used on the Time Scales map room, may be updated over time.