Regional Atmospheric Circulation and Patterns Associated With Extreme Floods in the Ukrainian Carpathians

Abstract

ABSTRACT

River floods in the mountainous regions of the Ukrainian Carpathians are a natural hazard that often leads to significant destruction and substantial economic damage to the region. The key driver of flooding is typically heavy rainfall, which results from certain patterns in regional atmospheric circulation. We studied the atmospheric circulation regimes over Ukraine for the period 1948–2021 using the modified Jenkinson–Collison classification. Circulation types associated with airflows from the western quarter are the most frequent throughout the year. However, seasonality in circulation patterns related to the dynamics of regional atmospheric centers of action is also well expressed. The linear trends in the frequency of circulation types are found statistically significant for meridional processes associated with advection from the north or south. Circulation types according to the Jenkinson–Collison classification, as well as the Niedźwiedź regional synoptic classification, were applied to cases of extreme floods in the river basins of the Ukrainian Carpathians to identify features of the pressure field leading to the formation of heavy precipitation. During the study period, 10 flood events, characterized by extremely high or historically significant water levels, were selected. Both pluvial floods in summer and mixed floods in winter were considered. In cases of the warm period, the circulation types with airflows directed towards the mountain range from the east or north are observed, and floods formed in the Ciscarpathia. In the cold period, circulation types with airflows from the western quarter increased precipitation and river discharge in Transcarpathia. 45% of observed circulation types belonged to the cyclonic group; however, the relative position of baric systems in other types also ensured the convergence of atmospheric moisture into the flood area.