FREQUENCY DISTRIBUTION OF PRECIPITATION 277 
Duration 
213 %o 
196 Min. 
I71 Ko 
mm 
a020 aaa 
Intensity 
Fre. 6—Schematical demonstration of two dimensional analysis of single 
rainfalls for Braunlage, Germany in June through August 1935-1950 
cases which do not belong to the hurricane rains 
or cyclonic rains are in good agreement with the 
theory. 
The detailed investigation of the group with 
excessive daily rain shows clearly two reasons 
for the produced rain and demonstrates again 
the complexity involved in rainfall sums. 
Refinement of analysis—The rainfall amount 
originally contains two parameters: intensity 
and duration. The recorded data are available in 
most instances for a predetermined constant 
duration such as hourly and daily sums. Very 
seldom a study is made which examines single 
rainfalls. Fortunately such a tabulation was 
available for Braunlage, Germany, in summer- 
time for the period 1935-1951 with approxi- 
mately 1000 values. A frequency analysis for 
both duration and intensity (in logarithmic 
scale) was made and the analysis exposed three 
partial collectives in both intensity and duration. 
About 20% have an average duration of 3% 
hr (log-normal distribution), the main part, in- 
cluding almost 50%, is just short of an hour, and 
the remaining 30% have an average of 4 hours. 
This may differ for other climatological regions, 
of course. The group division for the intensity 
proves to be slightly different as the parts are 
almost equal. One group is a little less with 
0.009 mm/min, (3.10 inch/min) while the other 
two show an average of 0.02 mm/min (10° inch/ 
min) and 0.063 mm/min (2.5.10° inch/min). 
In a two-dimensional analysis, the amount 
should now yield nine groups. But the analysis 
rendered three groups only. Hence, we may 
conclude that some of the groups may have 
been combined. Figure 6 demonstrates this fact. 
This is exactly similar to the result discussed 
for the daily precipitation amounts in Asheville 
in the preceding section where we discovered 
two physical processes in one group. Hence, a 
refinement of the analysis would be to separate 
the data by intensity and then split them into 
duration groups or vice versa. This takes for 
granted the knowledge of the various kinds of in- 
tensity or duration groups. Also a preparation of 
the observations in the form of single continuous 
rainfalls would be necessary. This is very diffi- 
cult, laborious and costly and there is little hope 
of accomplishing it. 
The alternative to the above-mentioned re- 
cording of data is to split the material into in- 
tensity groups by observation which means 
