## 3 Results
### Daily Analysis  
In Figure 6 the average daily rainfall for the whole study period is presented. Average values were calculated using all meteorological stations. The thick red and black lines resulted from smoothing raw IMERG and gauge average daily rainfall respectively so that trends can be easily analyzed. The smoothing procedure consists of applying locally weighted regression to scattered data [23]. In this figure, the dry and wet seasons during the study period can be easily noted. During the dry season (November to April [9]) average daily rainfall falls under 1 mm (see trend lines) and reaches higher values during the wet season. It is also shown that IMERG better represents the daily precipitation in the dry season and during the wet season IMERG mostly overestimates gauge data. Moreover, average daily rainfall values can reach over 18 mm/day during extreme precipitation events. In addition, Figure 6 shows the _COR_, _BIAS_ and _RMSE_ values calculated with IMERG and gauge daily rainfall data. A _COR_ value of 0.54 shows that daily IMERG estimates improve its agreement with respect to the hourly analysis. The bias indicates an overall overestimation of IMERG of 0.34 mm/day. Meanwhile an _RMSE_ value of 7.93 mm/day indicates that the deviations can be significant considering an average daily rainfall below 4 mm/day. Daily precipitation extremes have been also analyzed. Extreme rainfall events were determined by choosing the 98 th to 99.99 th percentile of the daily precipitation distribution from gauge data. Table 3 shows the statistics calculated for these data as compared with their corresponding IMERG 24-h precipitation estimates. The _BIAS_ and _RBIAS_ in Table 3 indicate that IMERG keeps underestimating rain gauges for extreme precipitation events. IMERG underestimates 46% of daily rain gauges, which is significantly less than that for the hourly analysis. The minimum daily precipitation considered here is about 27 mm/day; hence a deviation of 34.55 (see _RMSE_) shows also an improvement relative to the hourly analysis. The correlation (0.36) is also better than for the hourly analysis. Therefore, it can be said that IMERG accuracy improves with time scale from hourly to daily extreme precipitation events. Figure 6: Average daily rainfall (mm/day) for IMERG (thin pink) and gauge (thin gray) data from 1 April 2014 to 31 October 2015. Thick red and black lines resulted from smoothing raw IMERG and gauge data respectively. The _COR_, _BIAS_ and _RMSE_ values shown in the figure were calculated for these data. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Number. of Events** & **Min (mm/day)** & **Max (mm/day)** & **COR** & **BIAS (mm/day)** & **RMSE (mm/day)** & **RBIAS (\%)** \\ \hline
1141 & 26.92 & 180.59 & 0.36 & \(-\)21.03 & 34.55 & \(-\)46.00 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Extreme events statistics. Daily analysis. In addition, Figure 7 shows the absolute errors of the mean daily rainfall for each meteorological station and for precipitation intensities of 0-10 mm/day (solid cyan line), 10-25 mm/day (solid blue line) and 25 mm/day or greater (solid green line). These absolute errors were calculated using the mean values of the daily precipitation data (IMERG and gauge) for each station. They represent how much IMERG deviates from the gauge data. For example, the figure shows that for station 1 (x-axis) IMERG deviates from the gauge data in almost 5 mm/day for precipitation intensities of 25 mm/day or greater. Also, the absence of data in green and blue lines means that precipitation intensities corresponding to their respective ranges were not found for the corresponding meteorological station. What is worth noting in Figure 7 is that there is almost no deviation of IMERG from the precipitation observed when precipitation intensities are less than 10 mm/day. However, when precipitations are higher, the deviation can be over 15 mm/day. Also, there is no appreciable relation between this deviation and the elevation where a meteorological station is located.