*3.4. Temporal Performance of IMERG Products*

To explore the temporal characteristics of the calculated criteria for daily and monthly IMERG products, a monthly-based comparison was conducted using radar charts. It is noted that due to the similarity of the results for IMERG-Final and -Monthly, the monthly radar charts are separately displayed in the Supplementary Materials.

Figure 7a–h show a comparison of the eight criteria indices, including CC, rBIAS, MAE, FAR, POD, Under, Equal, and Over for each month considering IMERG-Early, -Late, and -Final products. The results show that, in general, there is a major temporal discrepancy in the criteria values obtained for different months. In most of the calculated criteria indices, the IMERG-Final shows noticeable improvements relative to IMERG-Early and -Late as compared to the rain gauge measurements.

**Figure 7.** Radar charts for criteria indices for IMERG daily products at the monthly time scale.

In the case of rBIAS (Figure 7a), it can be seen that the largest overestimation is in May for IMERG-Early (1.07) and IMERG-Late (0.98) while the overestimation reduced to 0.13 for the

IMERG-Final product. It seems that the applied corrected algorithm considerably reduced the bias for the Final product relative to Early and Late products. All three products showed largest MAE in March and the lowest MAE in July (Figure 7b). The lowest CC is observed for the summer months, June, July, and August, for all products (Figure 7c) while the highest CC is obtained for February (0.49), December (0.48), and October (0.46), which is consistent with the rBIAS results. The weak performance of the IMERG products with regard to the detection ability of the satellite relative to gauges in the summer months is noticeable in the POD and FAR indices (Figure 7d,e). The detectability of the satellite is the highest from February to May, with POD between 0.68 and 0.82. The lowest FAR is obtained for the same months, between 0.51 and 0.62 (Figure 7d,e). The under, equal, and over values show that from IMERG-Early to -Final, the percentage of the under index increased from May to August for which the over index decreased (Figure 7f–h). On the other hand, the under index decreased from November to March while the over index increased.
