Evaluation of precipitation measurements obtained from different types of rain gauges

Abstract

The results of parallel measurements of precipitation sums at the Polish Institute of Meteorology and Water Management - National Research Institute (IMWM-NRI), made by 4 types of automatic rain gauges (SEBA, A-STER, MET ONE and MPS) and a manual Hellmann rain gauge, indicate significa t differences between instruments. On average, the A-STER, MET ONE, MPS and SEBA rain gauges understate the precipitation sums relative to the Hellmann rain gauge annually by approximately 14 %; 13 %; 8 % and 5 %, respectively. The distribution of monthly and seasonal deviations of daily precipitation sums in automatic rain gauges relative to the Hellmann rain gauge indicates that regardless of the type of rain gauge, the largest negative deviations occur in the winter months, with a maximum of 20-25 %, and in MET ONE rain gauges even up to 30 %. The most common errors in automatic rain gauges are small errors (0.1 < daily sum < 1.0 mm). On average per year, they range from 45 % of days in SEBA rain gauges to 52 %-54 % of days in other types of rain gauges. Large errors (1.0 < daily total < 5.0 mm) are most common in A-STER, MET ONE, MPS and SEBA rain gauges. On average per year, they are approximately 16 %, 16 %, 7 % and 6 % of all days, respectively. The analysis of the deviations of the daily precipitation sums from automatic rain gauges relative to the Hellmann rain gauge indicates a clear asymmetry in their distribution. Negative deviations dominate over positive ones. The absence of differences occurs most often in SEBA rain gauges and amounts on average to 23 %. It occurs least frequently, at an average of 10 %, in MET ONE rain gauges. SEBA rain gauges are characterized by the smallest mean deviation value of the daily precipitation sums: -0.13 mm. In the MPS weighing rain gauges it is -0.26 mm. The largest mean deviations occur in the A-STER and MET ONE rain gauges, where they are respectively: -0.52 mm and -0.48 mm.