Grażyna Dąbrowska

Studies on precipitation intensity in Warsaw as a factor of road and traffic security

Characteristics of precipitation intensity in Warsaw in warm (May - September) and cold season (October - April) during 1977-1986 has been presented in the paper. Data has been collected at station of Warsaw-Okecie and differentiated due to type of precipitation (snow, rain, snow and rain etc.) to specify actual traffic conditions that has been a crucial factor of road safety.

The analysis of traffic conditions has required an assessment of intensity and time of occurrence in short time periods. While in warm period and hourly sum of precipitation, its intensity and time could be assessed basing on a direct measurements, in cold period it has been necessary to use (due to lack of data) indirect methods. To characterize precipitation in cold period author has used 6hour sum of precipitation from Hellmann's rain gauge and observations of intensity (three categories, so called subjective intensity), carried out by observers together with duration of precipitation and of its kind recorded in meteorological journal. The aim of this paper was to quantify subjective scale and to describe (statistically) a structure of intensity and duration of precipitation.

Following conclusions came out form the study (for warm period):

vast majority of precipitation cases - more than fifty percent - were those of continuous precipitation,

substantial part (ca. 60 percent) in total sum of precipitation was due to convective one,

this type of precipitation has had also maximum intensity (of about 0,0839 mm/min. as a mean)

while in cold period:

in general, rain (s) has the longest duration,

total sum of rain in total sum of precipitation has biggest part and highest intensity (about 0,0120 mm/min) for 6hour periods,

the overall intensity of precipitation is significantly bigger than this in warm period.