## 5 Conclusions  
In this research, the IMERG precipitation data have been evaluated over a Mexican region during the period between 1 April 2014 and 31 October 2015. This assessment has been made for different time scales (hourly, daily and seasonal) using precipitation gauges, as the reference data, from 99 automatic meteorological stations. The main conclusions of the study are summarized below:  
The IMERG hourly precipitation product is able to reproduce the diurnal cycle. A small agreement was found with respect to hourly rain gauges with an average _COR_ of about 0.35. IMERG tends to overestimate mean hourly values with relatively large deviations. For extreme values of hourly precipitation, its performance is quite poor with a _COR_ of 0.18 and a trend to underestimate rain gauges by 61%. IMERG shows better performance at the daily time scale resolution, with a _COR_ of 0.54. An overall bias of 0.34 mm/day over mean daily rain gauges was found. For extreme precipitation events the _COR_ (0.36) also improved with respect to the hourly analysis and a trend to underestimate daily rain gauges by 46% was observed. In addition, the deviations of IMERG are minima for precipitation intensities below 10 mm/day and they increase for precipitation rates over this value. The seasonal analysis showed good results, particularly for the dry season with a _COR_ of 0.69 and a positive bias of 1.11 mm. For the wet season a _COR_ of 0.51 and positive bias of 96.36 mm was found. For this season, very large deviations of IMERG may be expected. In terms of categorical statistics, the _FAR_, _POD_ and _CSI_ values were found to improve from hourly to daily time scales. The _FAR_ decreased from 0.7 to 0.4 approximately; the _POD_ values increased from 0.5 to 0.8 in average and _CSI_ values increased from 0.2 to 0.6. These statistics were also found to improve with topography. However, in this study this relationship becomes more evident for the daily than for the hourly precipitation. While _FAR_ values decreased with elevation, _POD_ and _CSI_ values behaved the other way around. According to this research, the IMERG hourly precipitation product should be used with caution over Mexico. Users should be aware of its poor performance, especially during heavy rainfall events. The daily and seasonal IMERG precipitation estimates are more reliable. Our findings differ from the suggestions of [PERSON] et al. [6] that IMERG would perform poorer over mountainous areas. This study found that IMERG tends to improve precipitation detection and to decrease magnitude errors over the higher terrain elevations of Mexico. This result could be highly influenced by a non-homogeneous distribution of gauges along the elevation ranges. In order to support our finding, it is advised to include all (daily and synoptic) rain gauges available in the country, which were disregarded in this study due to their relatively low time resolution. However insufficient and sparse these rain gauges are over the region, IMERG is not quite yet an accurate substitute for real observations. This research is, to our knowledge, the first study to evaluate IMERG precipitation data over Mexico and provides a reference for IMERG users on its performance. Consequently, it opens a window for future works regarding spatial verification of modeled precipitation and hydrological applications over the region. The results presented in this article are of great value to Mexico where the current precipitation data sources are still insufficient. Also, this study complements previous research and helps in improving our understanding of the IMERG database. The following are available online at www.mdpi.com/2072-4292/9/5/503/s1, Figure S1: Scatter plot for the 99.99 th to 100 th percentile of the hourly rain gauges. Rain gauges vs. IMERG from 1 April 2014 to 31 October 2015 over the Mexico region. Table S1: Hourly statistics analysis for 99.99 th to 100 th percentiles of the hourly precipitation distribution. Other supplementary materials are available upon request.