THE NORTH ATLANTIC OSCILLATION AND THE NORTH SEA–CASPIAN OSCILLATION INFLUENCE ON THE CLIMATIC FACTORS OF THE DNISTER RIVER RUNOFF FORMATION IN THE BEGINNING OF THE XXI CENTURY (UKRAINE)
Abstract
The relevance of the chosen topic stems from the impact of climate change on the water runoff of Ukraine’s rivers, among which the Dniester River plays a significant role. The Dniester supplies water to the south-western part of Ukraine and the Republic of Moldova. Climate change is primarily driven by the influence of climatic factors (precipitation and air temperature) on runoff formation. The aim of this study is to identify the role of atmospheric processes – the North Atlantic Oscillation (NAO) and the North Sea Caspian Pattern (NCP) – on the climatic factors influencing the Dniester’s runoff. The main research method is regression analysis. The moving average method was applied to identify cyclicality in the fluctuations of the indices. The study utilises hydrological and meteorological data from 1948, and for the joint analysis of time series – from 1955 to 2021. Since the available databases contain NCP indices only up to 2005, the authors extended the index series to 2021 in accordance with the methodology of Kutiel H., Benaroch Y. (2002). To calculate the NCP index for the period 2006–2021, ERA5 reanalysis data on geopotential at the 500 hPa isobaric surface (Z500) were used at the centres of the North Sea (55°N, 5°E) and the North Caspian Sea (45°N, 55°E). Data from thirteen meteorological stations (Mostyska, Yavoriv, Lviv, Stryi, Drohobych, Turka, Slavske, Kolomyia, Ivano-Frankivsk, Kamianets-Podilskyi, Ternopil, Liubashivka, Rozdilna) were analysed. It was found that the long-term average air temperatures at all meteorological stations are characterised by a statistically significant correlation with winter NAO indices. This indicates the influence of the North Atlantic Oscillation on the formation of the air temperature regime in the Dniester catchment along its entire length from the north-west to the south-east (within Ukraine). No links between NAO indices and precipitation characteristics have been established. The role of the NCP in shaping the Dniester’s annual runoff is less significant. A close inverse relationship has been established between annual precipitation totals and NCP indices for the upper reaches of the Dniester (Mostyska, Yavoriv, Lviv, Ivano-Frankivsk, Stryi, Drohobych). No such correlations were found for other meteorological stations. It has been shown that during the negative phase of NCP fluctuations, both precipitation and the flow of the Strv’yazh, Vereshchytsia and Shcherok rivers increase. This circumstance accounts for the distinctive characteristics of flow fluctuations in these rivers, in contrast to other tributaries of the Dniester. The established patterns will allow for a more accurate assessment of the prospects for changes in the flow of the Dniester’s tributaries under the influence of global atmospheric processes.References
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