A concept of nowcasting of convective precipitation using an X-band radar for the territory of the Zlín Region (Czech Republic)

Abstract

The paper presents the first results of precipitation nowcasting that is targeted to a smaller administrative unit in the Czech Republic (Zlin region), to aid better preparedness of the staff of crisis management of the region. The methodology is based on the scans of the X-band radar located at Holegov (240 m above the sea level). More specifically, the CAPPI 2000 data were used, which, in the first step, were converted into a 4-category system of warning classes (0: no event; 1/2/3: weak/moderate/strong events) for all the 13 smaller administrative districts of the region. Besides the radar echo extrapolation method TITAN that is operationally available in the region, a further extrapolation-based nowcasting method (COTREC) was selected and compared with a third approach (Persistence) that supposes no changes in the observed field of precipitation. The predictions of the CAPPI warning classes within the 13 districts with the lead times ranging from 5 to 30 min with 5 min intervals were compared with the observed CAPPI warning classes. Since the analysis was carried out in the framework of imbalanced ordinary regression, several issue-specific binary metrics had to be developed. Our first results indicate that the COTREC model outperformed the TITAN method, both in terms of the POD (probability of detection) and FAR (false alarm ratio) statistics, for all the lead times and the relevant binary metrics. Further we found that the reliability of the predictions sharply decreases with increasing lead times, and they are of low practical usability beyond the horizon of 30-40 min.