# Precipitation Products' Inter-Comparison over East and Southern Africa 1983-2017
## 4 Results  
### Cluster Analysis and Precipitation Seasonality  
The k-mean clustering method (Section 2.3) was used to identify homogenous sub-areas with respect to the annual precipitation cycle in the EA and SA regions. Eight clusters have been adopted for the EA region, as proposed in [37], but without the further subdivision of cluster 1 (see Figure 3a in [37]). [PERSON] et al. [37] have already demonstrated that the different zones (red zones in Figure 5a) which compose cluster 1 do not imply a variation of the precipitation seasonality but only a variation of precipitation amount. Figure 5a shows the spatial distribution of the clusters obtained from GPCC_Clim, while the corresponding precipitation annual cycles are presented in Figure 5b. As clearly evident in Figure 5 and previously described in Section 3.1, EA is characterized by a spatially highly variable monthly precipitation climatology. Clusters in eastern EA show bimodal annual cycles, with two precipitating seasons well separated by a dry period. This is the case in cluster 1, mainly covering Kenya and other areas around the west coast of Lake Victoria, Rwanda, the tip of the Horn of Africa, and a small coastal portion of Somalia, which is characterized by two precipitating seasons, i.e., with March-April-May (MAM) more intense and lower precipitation values in October-November-December (OND), separated by a dry season in June-July-August-September (JJAS) with precipitation lower than 40 mm month\({}^{-1}\). Cluster 3, including central Somalia together with a small area north of Lake Victoria, has an annual cycle similar to the previous one, with lower peak values in MAM and a second rainy season with a peak in October. Cluster 6, a coastal area located on southern Somalia and Kenya, and cluster 8, which includes northern Tanzania and  
Figure 4: Same as in Figure 2, but for SA. Burundi, show annual cycles analogous to cluster 1 but with more precipitation during the dry season in JJAS (cluster 6) and higher precipitation during January-February (JF) (cluster 8). Figure 5: Map of the EA clusters from GPCC_Clim data (**a**) and corresponding precipitation annual cycles for each EA cluster (**b**). Moving north-west, the dry season during the boreal summer tends to be reduced, with annual cycles characterized by a single precipitating season peaking in July and August, as is the case for clusters 5 (South Sudan and western Ethiopia) and 7 (northern Sudan), this latter with very scarce precipitation not greater than 40 mm month\({}^{-1}\). Clusters 2 and 4 represent areas characterized by transitional precipitation annual cycles, where two precipitation peaks develop without a real dry break in MAM and JJAS and in April-May and July-August for cluster 2 and 4, respectively. Cluster 2 encompasses central Ethiopia, the Rift Valley and escarpments of the Ethiopian Highlands, as well as small areas in Uganda and Kenya, whereas cluster 4 encompasses the coast of Somalia on the Gulf of Aden and the eastern range of the Ethiopian Highlands, the central region of Uganda and part of the Democratic Republic of the Congo. Figure 6 shows the annual cycles for the different precipitation products averaged over each cluster (Figure 5a), depicting the response of the satellite products to EA partitioning on the basis of precipitation seasonality. For each curve, the shaded areas represent the standard deviation associated with the monthly mean values, highlighting the spatial variability of the monthly precipitation within the indicated cluster. The verification of the homogeneity of the annual precipitation cycles (homogeneity in terms of precipitation seasonality) within each cluster was carried out for each satellite dataset considering the CCs between the annual precipitation cycle of each pixel of a given cluster and the average annual cycle of the same cluster. For each cluster and dataset, the mean CC value exceeds 0.8 with a \(p\)-value \(\leq\) 0.05 (confidence level \(\geq\) 95%).