# Precipitation Products' Inter-Comparison over East and Southern Africa 1983-2017
## 4 Results
### Temporal Stability of the Rain Detection and Estimation Capabilities  
The temporal evolution of the area-averaged statistical parameters (i.e., dichotomous and quantitative indices) was analyzed in order to evaluate the mutual stability of the precipitation products as a function of time. Starting from the daily time series of the three datasets, the statistical parameters were computed for each year and pixel and then averaged over the EA and SA regions. Figure 15 presents the annual evolution of dichotomous parameters (i.e., HK, POD, FAR and BIAS) relating to the EA region. Figure 14: Maps of CC (**a**), ME (mm day\({}^{-1}\)) (**b**) and MAE (mm day\({}^{-1}\)) (**c**) for SA. Different trends can be seen in Figure 15, with BIAS and FAR being the most variable indices over the 35 years examined. Similar behavior characterizes the intercomparisons of CHIRPS vs. TAMSAT3 and CHIRPS vs. MSWEP (Figure 15a,b), with a decrease in BIAS (from 1.2-1.3 to 0.9-1) and FAR (from 0.4-0.5 to 0.2-0.3) up to the end of the 1990s and a weak increase in the POD, especially for CHIRPS vs. TAMSAT3. This behavior is caused by the TAMSAT3 and MSWEP FA decrease as a function of time with respect to CHIRPS (not shown), followed by a stabilization of values starting in the year 2000. The situation is different for the TAMSAT3-MSWEP intercomparison (Figure 15c), where FAR decreases only slightly, from 0.4 to 0.3, but without the juxtaposition of the pre- and post-2000 behaviors, and BIAS increases up to 1.1-1.2 after an initial phase characterized by high variability, denoting the tendency to overestimate the number of precipitating days by TAMSAT3 with respect to MSWEP already mentioned in Section 4.2.1. In this case, TAMSAT3 misses with respect to MSWEP exhibit a negative trend over the whole period, whereas false alarms substantially decrease during 2000-2017 compared to 1983-1999 (not shown). Generally speaking, the HK index shows an increasing trend in all intercomparisons, indicating an increasing similarity among the three products in discriminating precipitating and non-precipitating days. An analogous convergence of the quantitative estimation capabilities of the three products with time is shown in Figure 16, with increasing CC and decreasing MAE values, especially for the intercomparisons with respect to CHIRPS (Figure 16a,b). The MAE values for CHIRPS vs. TAMSAT3 and CHIRPS vs. MSWEP intercomparisons, after a first phase characterized by a negative trend, stabilize around 1.5 mm day\({}^{-1}\) after 2000, whereas there is not a negative trend with time for the MSWEP vs. TAMSAT3 intercomparison (Figure 16c), but rather a variation in MAE from 1.5 to 2 mm day\({}^{-1}\) with a sort of decadal periodicity. MSWEP denotes a permanent underestimation with respect to CHIRPS with ME values in the range of [-0.25, 0.] mm day\({}^{-1}\) without any significant evolution with time (Figure 16b). Unlike this case, TAMSAT3 exhibits increasing ME values (Figure 16a,c); the tendency is more pronounced with respect to MSWEP (i.e., a progressing overestimation up to a maximum of 0.5 mm day\({}^{-1}\) during the whole period) than to CHIRPS, where TAMSAT3 overestimation takes place only after 2000. Considering the dichotomous parameters for SA, again an increasing similarity among the products is evident (see Figure 17). The MSWEP-CHIRPS pair shows the more stable values as a function of time, with only a weak increase in POD and HK and a decrease in FAR supported by a weak decrease in misses and false alarms for MSWEP with respect to CHIRPS (Figure 17b). Both intercomparisons involving TAMSAT3 present the typical decreasing tendency for BIAS and FAR, with the turning point in the year 2000 already observed in EA for CHIRPS vs. TAMSAT3 and CHIRPS vs. MSWEP, mainly due to a decreasing number of false alarms. Figure 15: EA-averaged annual HK, POD, BIAS and FAR (right y-axis) for TAMSAT3 with respect to CHIRPS (**a**), MSWEP with respect to CHIRPS (**b**) and TAMSAT3 with respect to MSWEP (**c**).