In our statistics, we quantified the number of days per km 2 on which
ΔH was greater than 3.5 km throughout the entire observation period
from 2005 to 2011. These days are referred to as radar-derived hail
days (RHD) to clarify the basis on which the statistics rely. Even if entire
hail streaks were determined from the 3D radar data, each grid point
was considered separately, independent of the surroundings. Tracking
was only used to interpolate between two consecutive radar images
as described above. Because hail at a specific location occurs only in extremely
rare cases more than once a day (if ever), the number of hail
days and the number of events are virtually identical (unlike the definition
of a thunderstorm day, for example). Note that even if the hail detection
criteria were calibrated and verified with insurance loss data, the
derived hail statistics are independent of this data set. This issue is crucial
and important for the reliability of the hail statistics presented since
insurance losses cannot be directly converted into hail probabilities or
intensities for several different reasons (see Section 2.3).