Spatio - Temporal Variability of Meteorological Droughts in Central Europe Considering Circulations Type

In the Polish Carpathians, periods of precipitation deficit have been observed, accompanied by an increasing frequency of dry months, particularly during the cold half of the year. Despite this, research addressing the spatial and temporal variability of meteorological droughts and the main mechanisms governing their occurrence in Central Europe remains limited.

The objective of this study is to analyze the spatial and temporal variability of droughts, expressed using the Standardized Precipitation Index (SPI), in the heterogeneous area of the Polish Carpathians and highland Region in East-Central part of Europe based on long term precipitation data. Additionally, for the first time, drought characteristics assessed using the SPI were discussed in relation to synoptic situation types (circulation types).

The study region is the Upper Vistula Basin located in the southern and south-eastern part of Poland. The area of this region is approximately 51,000 km2, i.e. a quarter of the entire Vistula basin. In this work monthly precipitation form 56 rainfall station were analysed from 1961 to 2022 years. Meteorological droughts were identified using Standardized Precipitation Index (SPI) calculated over 3-, 6-, 9-, and 12-month accumulation periods. For the 3-month SPI, the main climatic mechanisms responsible for extreme drought events were identified based on a circulation type calendar. Trends in extreme drought occurrence were detected using the Mann-Kendall test.

Statistically significant trends of SPI were observed on 52.7% of all analyzed stations, and in most cases, a positive trend was observed, indicating an increase in water resources in the Upper Vistula Basin. Such significant trends occurred more frequently at stations located in the western part of the analyzed region. Long-term droughts, represented by the 12-month SPI, were recorded at all stations, although not in all years. Short-term droughts, defined using the 3-month SPI, occurred most frequently during winter, while droughts based on the 6- and 9-month SPI were most common in winter and spring, and those represented by the 12-month SPI primarily occurred in winter and autumn.

The most intensive drought episode occurred in 1984, when drought conditions based on the 6-month SPI affected 98% of the analyzed region, and those based on the 9- and 12-month SPI covered approximately 90% of the entire region. Drought occurrence followed a clear seasonal pattern, with a dominant 10-year periodicity observed for all analyzed SPI timescales. In addition, Fourier analysis revealed a 2-year periodicity for the 3-, 6-, and 9-month SPI, and a 31-year periodicity for the 12-month SPI.

The results provide insights into the typical climatic conditions in Poland, characterized by strong precipitation seasonality. The study highlighted that short-term extreme droughts, represented by the 3-month SPI, are often caused by anticyclonic situations with high-pressure wedges Ka (anticyclonic wedge or ridge of high pressure) and Wa (west anticyclonic situation), as observed in 52.3% of cases. Overall, the findings provide valuable insight into the spatial and temporal variability of both short- and long-term extreme droughts in Central Europe, with particular relevance for the agricultural sector, which dominates the northern part of the analyzed region, where drought frequency is highest.