Spatial–temporal distribution of heavy precipitation over Ukraine during 1979-2019 according to the ERA5 reanalysis

A. B. Semerhei-Chumachenko; K. L. Slobodianyk

doi:10.31481/uhmj.26.2020.04

A. B. Semerhei-Chumachenko
K. L. Slobodianyk

DOI: https://doi.org/10.31481/uhmj.26.2020.04

Keywords: reanalysis data, ERA5, heavy precipitation, extreme precipitation, elementary circulatory mechanisms.

Abstract

The paper presents the results of research of heavy and extreme precipitation in the form of rain (> 50 mm / 12 h) and snow (> 20 mm / 12 h) using the data from the atmospheric reanalysis ERA5 for the period of 1979-2019. According to the data of the European Centre for Medium-Range Weather Forecasts obtained through the numerical modeling and resulting from the data assimilation at the nodes of a regular grid with a spatial resolution of 0,25°×0,25°, there are 131 and 136 days with rain and snow during which precipitation intensity reached the criteria of meteorological phenomena of the 2nd and 3rd levels of danger. It was discovered that the last 40 years in Ukraine proved to have a tendency of an increased number of cases of heavy snowfall, and a slightly decreased number of heavy rains.

The research pays considerable attention to the spatial-temporal analysis of the frequency and intensity of heavy rainfall with consideration of geographical factors. It determines the seasonal course of heavy and extreme precipitation, the maximum and minimum values of which did not differ from the climatic standard values observed during meteorological observations. Rainfalls with precipitation rates of more than 50 mm over 12 hours were observed almost over the entire territory of Ukraine and the maximum frequency zones were detected over the Carpathian Mountains, Donetsk Ridge, Podolsk Upland, and the south-western part of the country. Heavy snowfalls with more than 20 mm precipitation over 12 hours mostly occurred in the Carpathian region. The analysis of the geographical distribution revealed a center with maximum values of rain intensity (120-133 mm over 12 h) off the coast of the Sea of Azov, and the heaviest snowfalls (34-38 mm over 12 h) mainly formed in the Carpathian region.

The paper established the types of elementary circulation mechanisms of Dzerdzeevsky’s synoptic classification of Northern Hemisphere atmospheric circulation. These types, when continuous in nature, resulted in a significantly increased precipitation in the form of rain and snow.

According to the reanalysis data, cases with the maximum rain intensity were found over the period of 23 to 27 July 2008 when a catastrophic flood was observed in the Ukrainian Carpathians. This fact indicates that the structure of the field of heavy precipitation over the territory of Ukraine was adequately reproduced by the respective model of the European Centre for Medium-Range Weather Forecasts.

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