## 3 Results
### QPE Improvement  
#### 3.2.1 Rainfall Mapping  
The _qPrec_ software for quantitative precipitation estimation was developed in an iterative approach. Each upgrade or change of the software (e.g., incorporation of an additional QI, new input field, and modified algorithm) was validated against the 24-h precipitation amount from the network of about 600 climatological and pluviometric stations of the SHMU. A gradual expansion of the set of QIs in the _qRad_ software is mani  
Figure 4: Examples of visual improvements in a composite of several radars from the Central Europe (Slovakia, Hungary, Poland and Czech Republic). The column on the right (left) demonstrates a weather event from 5 August 2015, 13:10 UTC (19 August 2015, 12:30 UTC), by means of a composite of seven (nine) radars. The composites at the top are without quality information, whereas in the center, the quality information is incorporated in the process of compositing. The bottom line presents the corresponding fields of the final QIs. The CAPPI 2 km radar product was used: constant altitude PPI, i.e., a cross-section across a number of different PPI scans at the pre-defined altitude of 2 km above the ground. fested in the enhanced precision of the 24-h precipitation estimation by the _qPrec_ software. This fact is illustrated in Figure 5.  
Here, a traditional method of precipitation estimation based on the simple Marshall-Palmer relationship with no quality information (Figure 5 top) is compared with that derived by the _qPrec_ software, making use of the QIs (Figure 5 bottom), whereas the 'true' information on the precipitation amounts from the pluviometric stations are shown in both figures. The Marshall-Palmer conversion relationship between the reflectivity factor \(Z\) [mm\({}^{6}\)/m\({}^{3}\)] and the rainfall rate \(R\) [mm/h] was used in its simplest form:  
\[Z=200R^{1.6} \tag{8}\]  
Figure 5: A comparison of the 24-h rainfall measured with the network of \(\sim\)600 climatological and pluviometric stations in Slovakia (octagons) on 30 June 2017, with the estimation of those based on the radar data by means of a simple Marshall–Palmer relationship without quality information (**top**) and to the estimation of those by the _qPrec_ software with the calibrated reflectivity-rainfall-rate relation and quality information (**bottom**). There were significant differences in the radar-based estimation of the precipitation field (based on a composite of four radars located in Slovakia), mostly at the southern borders of Central and Eastern Slovakia, and in the Eastern parts of the country where the traditional Marshall-Palmer-based approach clearly overestimated the observed precipitation amounts. The QI-based estimation of the precipitation field, on the other hand, was much smoother, and successfully removed the majority of the non-meteorological signals as well as non-realistic estimates due to the bright band. A similar analysis is presented in Figure 6; however, instead of a 24-h accumulation, the focus is set on a long-term period, showing the comparison of the observed vs. estimated rainfall amounts for a 5-month period (1 May 2017-30 September 2017). The colored dots in the maps indicate the ratio \(r_{RG}\) of the radar-based estimation of rainfall amounts and the observed ones for three different approaches. A summary information on the frequencies of occurrence of the given values of \(r_{RG}\) is presented in Table 1.  
Figure 6: Ratios of the radar-based precipitation and the observed precipitation amounts for a long-term period (5 months, May to September, 2017) in Slovakia. The radar-based precipitation was estimated (**a**) using the Marshall–Palmer relationship, (**b**) by means of a calibration, but with no quality information, and (**c**) by means of a calibration, and with the quality information included. The analysis was based on 570 stations.