Precipitation extremes in the Ukraine: dynamical aspects, large-scale circulation and moisture sources

Abstract EGU General Meeting – April 2023

 

Abstract for session CL2.9: Atmospheric circulation in different spatial scales as one of the main climate variability factor

 

Precipitation extremes in the Ukraine: dynamical aspects, large-scale circulation and moisture sources

 

Ellina Agayar^1,2, Franziska Aemisegger¹, Moshe Armon¹, Alexander Scherrmann¹, and Heini Wernli¹

 

¹Institute for Atmospheric and Climate Science, ETH Zürich, Zürich, Switzerland

²Odessa State Environmental University, Odessa, Ukraine

 

 

 

Changes in the occurrence of large-scale circulation regimes link with changes in the global and regional climate and affect the frequency of occurrence and intensity of weather extremes, including extreme precipitation events (EPE). Understanding such natural hazards and their drivers is essential to mitigate related risks. In specific regions of the Ukraine, especially the Ukrainian Carpathians and the Crimean Mountains, precipitation can last for several days leading to floods. In this study, we investigate the dynamics of EPEs (≥ 100 mm day^-1) over the territory of Ukraine in the recent decades (1979-2019). The EPEs are identified based on precipitation observations from 215 meteorological stations and posts in Ukraine. The atmospheric parameters for the categorization of the weather types (WTs) associated with the EPEs, as well as for composite studies and trajectory calculations were taken from ERA5 reanalyses. The identification of moisture sources contributing to extreme precipitation in Ukraine is based on the computation of kinematic backward trajectories and the subsequent application of a moisture source identification scheme based in the humidity mass budget along these trajectories.

By analysing the large-scale atmospheric circulation from reanalysis products, a four-class weather type (WT) classification of days with extreme precipitations in Ukraine is performed. The largest values of precipitation and greatest likelihood of EPEs occur in the WTs “Southerly cyclones and troughs” (45.1%) and “Easterly and South-Easterly cyclones and troughs” (23.2 %). The resulting WTs are assessed in terms of frequency of occurrence, seasonality, thermodynamic structure, and the spatial pattern of the large-scale flow, which allow identifying the main mechanisms for the formation of EPEs over Ukraine. Results show a clear spatial division in EPE occurrence, with summer and autumn being the seasons of highest EPE frequency in the western, south-western and eastern Ukraine. The last part of this study is dedicated to defining the origin, uptake characteristics, and transport pathways of moisture that precipitates during EPEs in Ukraine.