Meteorological drought variability in the Upper Vistula Basin in period 1961-2022

Drought is a natural phenomenon affecting many aspects of human activity, such as water scarcity, food production, agriculture, industry, and ecological conditions. For decades, drought has caused significant financial losses in Europe and worldwide. In the Polish Carpathians, periods with rainwater deficits and an increasing frequency of dry months—especially in the cold half of the year—have been observed. However, there are limited studies on the spatial and temporal variability of meteorological drought in this area.

The aim of this study is to conduct a spatial and temporal analysis of drought, expressed as the Standardized Precipitation Index (SPI), in the heterogeneous region of the Polish Carpathians and the highland areas in East-Central Europe, based on long-term precipitation data. Monthly precipitation data from 30 rainfall stations, collected between 1961 and 2022, were analyzed. The SPI as an indicator of meteorological drought for 3-, 6-, 9-, 12-, 24-, and 48-month periods was calculated. The run theory was applied to identify the different drought events and to evaluate various drought characteristics: the number of drought events (N), the average drought duration (ADD), the average drought severity (ADS), and the average drought intensity (ADI).

As a result, N decreases with the increase of the time scale. In fact, a median of 59 and 15 events have been observed for the 3- and the 48-month SPI, respectively. The statistics of the ADD show an opposite behavior than N, with the lowest values corresponding to the 3-month SPI (median nearly 2 months) and the highest to the 48-month SPI (median of 8.8 months). Moreover, the variability in ADD increases with longer time aggregations. A similar behavior to ADD has been detected for the ADS at different temporal scales, with an average severity of 12.3 that occurred for the 48-month SPI. Finally, the ADI slightly decreases with the increase of the time scale, with the highest values observed for the 3-month SPI (1.48), and the lowest for the 48-month SPI (1.21).

The spatial distribution of the drought characteristics in the Upper Vistula Basin allows us to  identify the areas that could also face water stress conditions in the future, and which would thus require drought monitoring and adequate adaptation strategies. In particular, the northwestern part of the region, where soils have lower water-holding capacity and agriculture is more intensive than in the south, is particularly sensitive to drought.