Przegląd Geograficzny (2024) vol. 96, iss. 4
Variability of the Z-R relationship in monthly periods – to increase the accuracy of estimating the amount of precipitation using meteorological radars
Przegląd Geograficzny (2024) vol. 96, iss. 4, pp. 447-458 | 
Full text
doi: https://doi.org/10.7163/PrzG.2024.4.2
Abstract
The amount of precipitation in a catchment is the basic quantity used in modeling hydrological phenomena. So far, precipitation data has been most often obtained from rain gauges, which enable the measurement of only point amount of precipitation. An alternative to the use of rain gauges as a source of precipitation data is provided by meteorological radars, which provide data with high‑spatial resolution. However, radar measurement of precipitation are not accurate enough because it is an indirect measurement. Radars measure reflectivity, which, based on a specific Z-R relationship (i.e. between the values for reflectivity and intensity of precipitation), is converted into the amount of precipitation. The main limitation in the estimation of precipitation using radars is attributed to the high variability of the Z-R relationship in time and space. Disdrometers, which enable the determination of the Z-R relationship on the basis of the reflectivity and intensity of precipitation, are of fundamental importance to the improved calibration of meteorological radars.
Measurements of reflectivity and precipitation intensity, carried out at the Meteorological Station of Warsaw University of Life Sciences using the Parsivel1 laser disdrometer, were the basis for the determination of the relationships between these quantities (parameters a and b for the Z-R relationship) for each individual month (in the April‑October periods) in the years 2012‑2014 and 2019‑2020.
The values of the a parameter for the Z-R relationship determined as a result of the research significantly differed for individual months. They ranged from 199 to 493, and their arithmetic mean was 311. Moreover, the values of the a parameter varied considerably for corresponding months in different years. On the other hand, the values of the b parameter were within a narrow range, i.e. from 1.30 to 1.56, with the mean value of 1.45. The determined values of the a and b parameters were consistent with those found in the literature. The range of the variability of the b parameter was so small that its uncertainty can be perceived as insignificant. These results suggest that assuming a constant value for parameter b is justified, meaning the variability of the Z‑R relationship can be accounted for solely by changes in parameter a. This simplifies the implementation of the Z-R relationship in the operational work of a meteorological radar. The results of these studies indicate the need to take into account the variable values of the a parameter for the Z-R relationship in relation to various monthly periods in the radar data processing procedure. However, it is necessary to carry out analyses that will allow to assess the impact of such activities on increasing the accuracy of estimating the amount of precipitation using meteorological radars.
The maximum individual values of the a parameter were recorded in July, August and October. Whereas, the highest mean values of the a parameter, calculated on the basis of its values for the corresponding months in the years 2012‑2014 and 2019‑2020, were obtained for data sets from June, July and August. This means that the highest values of this parameter generally occurred in periods with frequent convective precipitation. In the current research, an attempt was made to link the values of the a parameter for individual months (determined separately for 30 months) with the values of basic statistical measures (including the maximum and arithmetic mean), which were calculated on the basis of instantaneous values of reflectivity and intensity of precipitation for the relevant months. It was fund that there is a strong correlation between the values of the a parameter for Z-R relationship for individual months and the mean monthly reflectivity (expressed in mm6 m−3 units) – the correlation coefficient is R = 0.70. The obtained relationship between these quantities requires verification in terms of its suitability for the calibration of radar images.
Keywords: laser disdrometer, reflectivity and precipitation intensity, Z-R relationship, meteorological radar cali- bration, precipitation amount, hydrology
[mariusz_barszcz@sggw.edu.pl], Szkoła Główna Gospodarstwa Wiejskiego w Warszawie, Instytut Inżynierii Środowiska
Citation
APA: Barszcz, M. (2024). Zmienność zależności Z-R w okresach miesięcznych – dla zwiększenia dokładności szacowania wielkości opadów za pomocą radarów meteorologicznych. Przegląd Geograficzny, 96(4), 447-458. https://doi.org/10.7163/PrzG.2024.4.2
MLA: Barszcz, Mariusz Paweł. "Zmienność zależności Z-R w okresach miesięcznych – dla zwiększenia dokładności szacowania wielkości opadów za pomocą radarów meteorologicznych". Przegląd Geograficzny, vol. 96, no. 4, 2024, pp. 447-458. https://doi.org/10.7163/PrzG.2024.4.2
Chicago: Barszcz, Mariusz Paweł. "Zmienność zależności Z-R w okresach miesięcznych – dla zwiększenia dokładności szacowania wielkości opadów za pomocą radarów meteorologicznych". Przegląd Geograficzny 96, no. 4 (2024): 447-458. https://doi.org/10.7163/PrzG.2024.4.2
Harvard: Barszcz, M. 2024. "Zmienność zależności Z-R w okresach miesięcznych – dla zwiększenia dokładności szacowania wielkości opadów za pomocą radarów meteorologicznych". Przegląd Geograficzny, vol. 96, no. 4, pp. 447-458. https://doi.org/10.7163/PrzG.2024.4.2