## 3 Results
### Hourly Analysis  
Figure 2 describes the variation of the mean hourly rainfall for the studied period and for all meteorological stations where gauge and IMERG data were computed. Highest values of the mean hourly rainfall are found during the late afternoon and night-time hours. The lowest values correspond to hours between 07:00 and 20:00 UTC hours, reaching a minimum between 15:00 to 17:00 UTC hours. Additionally, a lag of approximately 2 h between the hourly minimum and maximum peaks of the IMERG and the rain gauge data is observed. Moreover, where higher values are found, IMERG seems to overestimate gauge data, while it underestimates gauge data for lower mean hourly precipitations. Overall, it can be seen that the IMERG data reproduce the daily cycle of the average precipitation over the study area fairly well, although it appears that the IMERG product behaves differently (with respect to gauges) during daytime and night-time hours. Also, hourly correlation (blue), bias (yellow) and root-mean-square error (green) average values are presented in Figure 2. Mean statistics were computed for each hour and for all meteorological stations. In Figure 2, it is shown that hourly correlations range from 0.25 to 0.5. Biases are close to 0 mm/h with a slight trend for IMERG to overestimate gauge data during night-time hours. As shown in Figure 2 the \(RMSE\) values range from 0.2 to 1.5 mm/h and follow IMERG hourly trends. Note that minimum values for \(RMSE\) are found during daytime hours when correlations are higher. IMERG's ability to capture extreme rainfall events has been also analyzed in this study. For this, the 98 th to 99.99 th percentile of the observed precipitation values have been compared with their corresponding IMERG estimates. Table 2 shows the statistics resulting from this comparison. Here, a bias of \(-2.7\) mm/h indicates that IMERG tends to underestimate extreme precipitations. The \(RBIAS\) shows that IMERG precipitation estimates account for only 61% of the mean rain gauges for precipitation intensities between 1.2 and 35.79 mm/h. In addition, the \(RMSE\) indicates that mean deviations are higher than 5 mm/h, which is considered large because it is four times higher than the  
Figure 2: Average hourly rainfall (mm/h) for Integrated Multi-satellite Retrievals for Global Precipitation Measurement (IMERG) (red) and Gauge (black) data for the period 1 April 2014 to 31 October 2015. Hourly average statistics results are shown. Pearson correlation coefficient (\(COR\)): blue; bias (\(BIAS\)) (mm/h): yellow; and root-mean-square error (\(RMSE\)) (mm/h): green, for the same period. minimum (1.2 mm/h) and also because of the weak correlation value of 0.18. We also analyzed the behavior of the very extreme rainfall events (cases above the 99.99 th percentile) with similar results (See Figure S1 and Table S1). Here the underestimation of IMERG increased remarkably to 89%. Also in this section, continuous and categorical statistics are used to describe the IMERG characteristics with respect to gauge locations. This analysis gives a spatial perspective of the IMERG behavior. To this end, Figure 3 shows correlations statistics. Figure 3a shows correlations as a function of the location of the meteorological stations, colors are given by correlation intervals; Figure 3b is a scatter plot diagram for gauge vs. IMERG hourly precipitations for all meteorological stations and Figure 3c shows the actual correlations values (red line) for each meteorological station, which have been ordered following their elevations (gray, shaded area). The regression line (in black) shown in Figure 3c describes the relationship between the correlation and topography. It can be noted from Figure 3a that most meteorological stations show correlation values between 0.2 and 0.4. However, a slight trend is observed for some meteorological stations located at higher elevations to have correlation values below 0.2, while some others closer to the coast and located at lower elevations show correlation values higher than 0.4.