# Precipitation Products' Inter-Comparison over East and Southern Africa 1983-2017
## 4 Results
### Cluster Analysis and Precipitation Seasonality
From a first qualitative analysis of the graphs in Figure 6, it is possible to observe a general tendency of MSWEP to underestimate precipitation compared to the other two datasets, whereas a greater agreement between CHIRPS and TAMSAT3 emerges. The MSWEP underestimation is particularly evident during the precipitation peak months in western EA (cluster 5), but it appears also during the transition between the two rainy seasons, as in clusters 4 and 6. Clusters 2, 4 and 5 are characterized by the greatest intra-cluster variability (i.e., high standard deviation values). The terrain complexity of these areas, with highlands and escarpments, motivates this high variability. To quantify the differences presented in Figure 6, monthly ME and MAE were computed for each cluster, comparing the monthly climatology of the precipitation products pixel by pixel and then spatially averaging monthly ME and MAE on each cluster (Figure 7). The agreement between the TAMSAT3 monthly climatology with CHIRPS is confirmed in Figure 7a,b, with the lowest overestimation of monthly precipitation by TAMSAT3 (ME \(<\) 10 mm month\({}^{-1}\) except for cluster 4 in July and October) and a more marked underestimation from April to June for clusters 6 and 8. This translates into MAE values generally lower than 10 mm month\({}^{-1}\) except for clusters 1, 4, 6 and 8, during the rainy seasons. Looking at the comparisons between MSWEP and CHIRPS (Figure 7c,d) and TAMSAT3 with respect to MSWEP (Figure 7e,f), it is evident how MSWEP systematically underestimates monthly precipitation compared to the other two datasets, with the major MEs found in cluster 5 for the months of July and August. The greatest MAE values come from TAMSAT3 with respect to MSWEP, exceeding 30 mm month\({}^{-1}\) in clusters 1 and 8 in April, and cluster 5 in July and August. The k-mean clustering method was exploited to subdivide the SA territory into homogeneous sub-areas with respect to the annual precipitation cycle. Figure 8a shows the six identified clusters, whereas in Figure 8b the corresponding average annual precipitation cycles from the GPCC_Clim data are presented. Different numbers of clusters were tested in order to obtain the best compromise between the minimization of the intra-cluster variance and excessive fragmentation of the territory. A further increase in the number of clusters out of the six identified resulted only in a further fragmentation of cluster 2, creating two transition zones at the boundary with cluster 3 (i.e., RSA at the boundary with Botswana and Zimbabwe, and northern Angola with the southern Democratic Republic of Congo). Moreover, the corresponding monthly climatology of these transition zones was almost identical to that of cluster 3, with slightly lower quantities in January and February. Figure 6: _Cont._  
SA is characterized by a more homogeneous precipitation seasonality than EA, as shown in Figure 8b, but with variable precipitation amounts. With the exception of cluster 6, which includes the Cape Town region, all clusters show very similar monthly climatology, characterized by a wet season occurring during the austral summer from October to March (ONDJFM) and a dry season coinciding with the austral winter from April to September (AMJJAS). Cluster 1, which includes the pre-desert region in Namibia, northern Mozambique and the northwestern coast of Madagascar, and cluster 3, covering central Madagascar and central SA, are characterized by very similar precipitation annual cycles, with a dry season from May to October with very low precipitation and a rainy season coinciding with the period ONDJFM and culminating during JF. Cluster 3 is slightly more abundant in precipitation than cluster 1 during the early phase of the rainy season in OND. Cluster 2, which includes northern Angola, Eastern RSA at the boundary with Botswana, Zimbabwe, Mozambique, and south-central Madagascar has a shorter dry season from May to August, and is characterized by more abundant rainfall compared to clusters 1 and 3 in the period of September-November.