## 3 Comparative Analyses Results
### Rain-Gauge vs. Radar Observations
#### 3.1.3 PANTHERE and OPERA vs. RADOME  
Over France, the rain amounts provided by both PANTHERE and OPERA radar products were based on a quasi-identical radar network. These differences between the two radar products could reside in the processing applied by Meteo-France, for PANTHERE, and by EUMETNET, for OPERA. The rain accumulated patterns were quite similar in PANTHERE (Figure 4a,b) and OPERA (Figure 5a,b) for both cases, but there were few differences locally. In order to better quantify the differences in the rain estimates from both radar products compared to the rain-gauge observations, Figure 6 presents the absolute biases obtained using OPERA compared to those obtained using PANTHERE as a function of the RADOME values for both cases (without distinguishing the areas defined in Figure 2c). Figure 6 shows that OPERA provided generally higher rain amounts than PANTHERE for both cases. For the April case, both radar products tended to agree with the RADOME observations when rain gauges captured rain amounts up to 20 mm but the main differences appeared when rain gauges captured rain amounts higher than 40 mm. In that case, both radar products greatly underestimated (by more than \(-20\) mm) the rain amounts. We can also note that the observations of a few rain-gauge stations seem greatly underestimated by OPERA, while PANTHERE provided rain values less underestimated or slightly overestimated (dashed red line in Figure 6a). For the June case, Figure 6b shows that the  
Figure 6: Comparison of the biases obtained between both radar products (OPERA and PANTHERE) and the RADOME rain-gauge network. Colours correspond to the accumulated precipitation values observed by the RADOME rain gauges for both (**a**) the April and (**b**) the June cases. The grey dashed line represents the 1:1 curve. The red dashed line corresponds to a specific situation defined in the text. absolute biases were between \(-20\) mm and \(+20\) mm with PANTHERE, whereas they were between \(-20\) mm and \(+40\) mm with OPERA (compared with RADOME observations). Moreover, Figures 4a,b and 5a,b, show that even though both radar products well-detected the presence of precipitation over the reliefs of the south of France or over the north of the Massif Central for the April or the June case, respectively (as in RADOME, Figure 2a), a few major differences could be observed. Indeed, for the April case, the zone where the rain accumulation was greater than 55 mm was more extended in OPERA (Figure 5a) than in PANTHERE (Figure 4a), and OPERA recorded light precipitation accumulations (\(<\)3 mm) in the north of France, whereas a larger no-precipitation zone was observed by PANTHERE. For the June case, Figure 5b shows that the zone where the rain amounts were greater than 100 mm was more extended in OPERA than in PANTHERE, explaining that the important difference in the mean absolute bias calculated over the NMC was with the two radar products (Table 3). Note that the field of the high accumulated rain amounts at the surface seemed more discontinued in OPERA than in PANTHERE (e.g., over the northeast of France in Figure 5b compared to Figure 4b), which was due to the different spatial resolutions of the two radar products (see Table 1). Focussing on the specific areas defined in Figure 2c for the April case, OPERA maximum estimates were higher than the PANTHERE ones for the WMC, DUR, CEV, and JUR (Table 2). We can also note that even if the mean absolute biases were quite comparable for WMC, SAL, and CEV in the PANTHERE and OPERA products, the trends were opposite for two of them (Table 3). Moreover, the differences in the rain amounts estimated by both radar products became more striking for DUR and JUR (see Table 3). Indeed, for these specific areas, the median of the accumulated rain amounts was equal to 28.0 mm in PANTHERE and 16.11 mm in OPERA for DUR, while it was equal to 22.6 mm in PANTHERE and 27.63 mm in OPERA for JUR. Figures 4a and 5a also show that the rain distributions were quite different over these two specific areas for the April case.