2.3.4. Geospatial and Temporal Analysis

The difference between the IMERG products and rain gauge measurements may depend on geospatial conditions, time of the year, and the rainfall nature at the different geospatial locations. To investigate this dependency, the evaluation indices presented in Section 2.3.2 were calculated for different categories of geospatial factors, such as the elevation, slope, latitude, and longitude of satellite grids corresponding to rain gauges locations. The evaluation was carried out for additional factors, including the average annual rainfall, mean dry period (intervals between rainfall events), and rainfall index (average annual rainfall/mean dry period) for stations representative of the frequency and amount of rainfall at a given location. For simplicity, a location with a lower or higher rainfall index is, alternatively, mentioned as a dryer or wetter location, respectively.

We used box plots to illustrate the variation of the indices for 10 different categories of rain gauges. These categories were based on selecting 11 range limits of a given geospatial factor so that an equal number of rain gauges was placed into each category (37 rain gauges out of the selected 370 synoptic stations). Therefore, the 1st and the 11th limits were the minimum and the maximum values of the geospatial factor among the selected locations of the study.

Further, the spatiotemporal evaluations were separately reported for each month and season using combined maps. That is, plotting the spatial variation of the indices, e.g., POD, and, at the same time, the factors, e.g., topography, for a given month or season in a single map.
